PBN TRAINING FOR OPERATIONAL ATS PERSONNEL

Transcription

1 PBN TRAINING FOR OPERATIONAL ATS PERSONNEL SA PBN Implementation Project

2 REVISION INDEX Version Revision Date Reason for Change Pages Affected Draft /05/2010 New Document by Zach Froneman All Draft /05/2010 Amended by Zach Froneman All Draft /05/2010 Amended by Zach Froneman All Draft /05/2010 Amended by Zach Froneman All Draft /05/2010 Amended by Elsabé Wait & Zach Froneman Draft /05/2010 Amended by Zach Froneman All Draft /05/2010 Amended by Zach Froneman All Draft /05/2010 Amended by Elsabé Wait & Zach Froneman Draft /05/2010 Amended by Elsabé Wait & Zach Froneman Draft /05/2010 Amended by Elsabé Wait & Zach Froneman Draft /05/2010 Amended by Zach Froneman All Draft /06/2010 Amended by Elsabé Wait, Pamela Johnson & Zach Froneman Draft /06/2010 Amended by Zach Froneman All Draft /06/2010 Amended by Zach Froneman All Draft /06/2010 Amended by Elsabé Wait, Pamela Johnson & Zach Froneman Draft /06/2010 Amended by Elsabé Wait, Pamela Johnson & Zach Froneman Draft /06/2010 Amended by Zach Froneman Sec. 4 Draft /06/2010 Amended by Zach Froneman Sec. 4 & 5 Draft /06/2010 Amended by Zach Froneman All Draft /07/2010 Amended by Howard Hawk, Wayne Lessard & Zach Froneman Draft /07/2010 Amended by Zach Froneman, formatting changes All All All All All All All All All ATNS/HO/C09/30/02/01 Page 2 of July 2010

3 EXECUTIVE SUMMARY The primary aim of this manual is to provide the operational ATS personnel with the required theoretical knowledge to progress to the practical placation and use of PBN based RNAV procedures in the daily provision of Air Traffic Services. We will discuss the development from basic conventional navigation through to the possible application of Performance-Based Navigation (PBN) as proposed by the International Civil Aviation Organisation (ICAO). It also aims at providing the required reference material for the reader to familiarise him or herself with the development, application and implications of widespread Area Navigation (RNAV) application in a modern Air Traffic Management (ATM) System. Recognising the current level of understanding of RNAV application, this manual will explain the flight deck RNAV capabilities as well as the means to guarantee the navigation performance. This manual will also explore the possible changes to the way in which ATM is provided at the moment as well as to explain the expected benefits to the wider ATM community of increased use of the full RNAV capabilities now available. This manual is the first step towards the PBN training prescribed for operational Air Traffic Service (ATS) by The ICAO. The second step will include simulation exercises that will demonstrate in a practical manner the benefits of maximising RNAV applications. The Body of the Document starts on Page 25 ATNS/HO/C09/30/02/01 Page 3 of July 2010

4 REFERENCES ICAO Manuals: Doc 9613 Doc 9905 Doc 9849 Doc 9689 Doc 9573 Doc 9854 Doc 9750 Performance-Based Navigation Concept and Implementation Manual RNP AR Approach Design (Draft) GNSS Manual Manual on Airspace Methodology and Sep Minima Manual of Area Navigation (RNAV) Operation 1ed ATM Operational Concept Global Air Navigation Plan South African National Airspace Master Plan ATNS ATM Roadmap. SA PBN Implementation Roadmap An Introduction to GNSS, Charles Jeffrey, P. Eng., NovAtel Inc, Internet sites: Engineering solutions from the GNSS community Andrews Space and Technology (AST) Wikipedia, The Free Encyclopedia The International GNSS Service (IGS) United Nations Office for Outer Space Affairs, International Committee on Global Navigation Satellite Systems Global Positioning System, Serving the World Spaced-based Positioning Navigation & Timing 8051 Forum (Micro-controller projects) traffic commercial/aeromagazine/ Sharing Earth Observation Resources GNSS Applications and Methods Federal Aviation Administration; GNSS Library ATNS/HO/C09/30/02/01 Page 4 of July 2010

5 TABLE OF CONTENT REVISION INDEX... 2 EXECUTIVE SUMMARY... 3 REFERENCES... 4 TABLE OF CONTENT... 5 ABBREVIATIONS... 8 EXPLANATION OF TERMS AREA NAVIGATION (RNAV) SYSTEMS Background Conventional Navigation Methods and Procedures RNAV Navigation Methods and Procedures WGS - 84 Geodetic Reference Datum Historical Overview Future Air Navigation System (FANS) Aircraft Area Navigation (RNAV) Computer System Function Navigation Navigation Database Flight Planning Guidance and Control Display and System Control Manual Radio Position Updating Automatic Radio Position Updating Area Navigation (RNAV) Operations RNAV Routes RNAV Waypoint types Required Navigation Performance (RNP) Specification Functional Capabilities and Limitations RNAV System Requirements in terms of Accuracy, Integrity and continuity RNAV and RNP Specific Functions RNAV Leg types Fixed Radius Paths Holding Pattern Offset Flight Path GLOBAL NAVIGATION SATELLITE SYSTEMS (GNSS) Description of the GNSS Concept Almanac GNSS Segments System Accuracy, Integrity, Continuity and Availability Signal Performance Requirement Augmentation Ground-Based Augmentation System (GBAS) Aircraft-Based Augmentation System (ABAS) ATNS/HO/C09/30/02/01 Page 5 of July 2010

6 2.3.3 Space-Based Augmentation System (SBAS) Ground-Based Regional Augmentation (GRAS) Techniques to improve GNSS receiver performance GNSS Liability Description of Receiver Display Functionality Integrity Alerts NAVSTAR GPS (Navigation Signal Timing and Ranging Global Positioning System) GLONASS (Global Navigation Satellite System) GALILEO (The name given to the European Global Navigation Satellite System) Other Navigation Satellite Systems China India Japan France ALL WEATHER OPERATION Conventional NAVAID Based Procedures Standard Instrument Departures (SIDs) and Standard Terminal Arrival Routes (STARs) The Non-Precision Approach (NPA) The Precision Approach (PA) Continuous Descent Approach (CDA) Non-Conventional NAVAID Based Procedures (RNAV Approaches) Overlay Procedures Concept Standard Instrument Departures (SIDs) and Standard Terminal Arrival Routes (STARs) Sensor Specific Area Navigation (RNAV) Procedures RNP Procedures (Pre-PBN) THE PERFORMANCE BASED NAVIGATION CONCEPT Description of Performance Based Navigation Introduction Navigation Specification NAVAID Infrastructure Navigation Application Future Developments Airspace Concept Introduction The Airspace Concept Airspace Concepts by Area of Operation Stakeholder Uses of Performance Based Navigation Introduction Airspace Planning Instrument Flight Procedure Design Airworthiness and Operational Approval Implementation Guidance ATNS/HO/C09/30/02/01 Page 6 of July 2010

7 4.4.1 Introduction to Implementation Process Process 1: Determine Requirements Process 2: Identifying the ICAO Navigation Specification for Implementation Process 3: Planning and Implementation Guidelines for Development of a New Navigation Specification CHANGES IN ATS DELIVERY DUE TO PBN IMPLEMENTATION ATS Flight Plan Requirements Conventional Navigation Non-Conventional Navigation Designation of RNAV Routes ATS Procedures Control Procedures Contingency Procedures Separation Minima Longitudinal Lateral Mixed Equipage Environment Transition Between Different Operation Environments Phraseology Reporting of Gross Navigational Errors RNAV STARs and SIDs Related Control Procedures Radar Vectoring Techniques Open and Closed STARs Altitude Constraints Descend/Climb Clearances RNP Approach and Related Procedures Impact of Requesting a Change to Routing during a Procedure Fix/Waypoint Naming NAVAID Infrastructure Status Monitoring ATS System Monitoring ATNS/HO/C09/30/02/01 Page 7 of July 2010

8 ABBREVIATIONS ABAS ACARS ADS-B ADS-C AFM AIP ANSP APV ATM ATS Baro-VNAV bps C/A Code CDGPS CDI CDU CFIT COSPAS DGNSS DPGS DME DOP DR DTED EASA ECAC ECEF EGM ESA EUROCAE Aircraft-based augmentation system Aircraft Communications Addressing and Reporting System Automatic Dependent Surveillance Broadcast Automated Dependent Surveillance Contract Aircraft Flight Manual Aeronautical Information Publication Air Navigation Service Provider Approach Procedure with Vertical guidance Air Traffic Management Air Traffic Service(s) Barometric Vertical NAVigation. Bits per Second Coarse/Acquisition Code Canada-Wide Differential GPS Course Deviation Indicator Control and Display Unit Controlled Flight Into Terrain Cosmitscheskaja Sistema Poiska Awarinitsch Sudow (Russian: space system for search of vessels in distress) Differential Global Navigation Satellite System Differential Global Positioning System Distance Measuring Equipment Dilution Of Precision Dead Reckoning Digital Terrain Elevation Data European Aviation Safety Agency European Civil Aviation Conference Earth-Centred-Earth-Fixed 1996 Earth Gravitational Model (EGM96) European Space Agency European Organisation for Civil Aviation Equipment EUROCONTROL European Organisation for the Safety of Air Navigation FAA FAS FDE FDMA FMS Federal Aviation Administration Final Approach Segment Fault Detection and Exclusion Frequency Division Multiple Access Flight Management System ATNS/HO/C09/30/02/01 Page 8 of July 2010

9 FOC FTE FRT GAGAN GBAS GEO GHz GLONASS GNSS GPS GRAS GRS HEO ICAO IERS INMARSAT INS IOV IRNSS IRS IRU JAA L1 L1C L1F L2 L5 LAAS LNAV Mb MB MCDU MEL MHz MNPS ms MSA MTSAT NAVAID Full Operational Capability Flight Technical Error Fixed Radius Transition GNSS Aided GEO Augmented Navigation (India) Ground-Based Augmentation System GEOstationary orbit GigaHertz GLObal NAvigation Satellite System Global Navigation Satellite System Global Positioning System Ground-based Regional Augmentation System 1980 Geodetic Reference System (GRS80) Highly Elliptical Orbit International Civil Aviation Organisation The International Earth Rotation and Reference Systems Service International Maritime Satellite Organisation Inertial Navigation System In-Orbit Validation Indian Regional Navigation Satellite System Inertial Reference System Inertial Reference Unit Joint Aviation Authorities The MHz GPS carrier frequency including C/A and P-code Future GPS L1 civilian frequency Future Galileo L1 civilian frequency The L2 civilian code transmitted at the L2 frequency ( MHz) The MHz 3 rd civil GPS frequency that tracks carrier at low signal-to-noise ratios Local Area Augmentation System Lateral NAVigation Megabit Megabyte Multifunction Control and Display Unit Minimum Equipment List MegaHertz Minimum Navigation Performance Specification millisecond Minimum Sector Altitude Multi-functional Transport SATellite NAVigation AId (also used as NAVAID) ATNS/HO/C09/30/02/01 Page 9 of July 2010

10 NAVSTAR NM NPA ns NSE PA PBN P-code PDE PE-90 POH PPS PRN# PSR PS-90 RAIM RF RNAV RNP RTK SAR SARSAT SBAS SID SSR SNAS SOL SPS STAR SV TLS TSE UHF UTC UTC(SU) VDB VHF VNAV VOR NAVigation Satellite Timing and Ranging (synonymous with GPS) Nautical Mile Non-Precision Approach nanosecond Navigation System Error Precision Approach Performance-Based Navigation Precision code Path Definition Error Parameters of the Earth 1990 (see PS90) Pilot Operating Handbook Precise Positioning Service Pseudo-Random Noise Number Primary Surveillance Radar Parametry Semli 1990 (see PE-90) Receiver Autonomous Integrity Monitoring Radius to fix Area NAVigation Required Navigation Performance Real Time Kinematic Search And Rescue Search And Rescue Satellite Aided Tracking Satellite-Based Augmentation System Standard Instrument Departure Secondary Surveillance Radar Satellite Navigation Augmentation System (China) Safety-Of-Life Standard Positioning Service STandard instrument ARrival Space Vehicle Target Level of Safety Total System Error Ultra High Frequency Coordinated Universal Time Coordinated Universal Time (former Soviet Union, now Russia) VHF Data Broadcast Very High Frequency Vertical NAVigation Very high frequency (VHF) Omnidirectional radio Range ATNS/HO/C09/30/02/01 Page 10 of July 2010

11 WAAS WGS WPT QSSS Wide Area Augmentation System World Geodetic System WayPoinT Quasi-zenith Satellite System ATNS/HO/C09/30/02/01 Page 11 of July 2010

12 EXPLANATION OF TERMS Absolute Accuracy. In GNSS positioning, absolute accuracy is the degree to which the position of an object on a map conforms to its correct location on the Earth to an accepted coordinate system. Acquisition. The process of locking onto a satellite s C/A code and P-code. A receiver acquires all available satellites when it is first powered up, then acquires additional satellites as they become available and continues tracking them until they become unavailable. Aircraft-Based Augmentation System (ABAS). An augmentation system that augments and/or integrates the information obtained from the other GNSS elements with navigation information available on board the aircraft. Note: The most common form of ABAS is receiver autonomous integrity monitoring (RAIM). Aircraft Communications Addressing and Reporting System (ACARS). This is a digital data link system for transmission of short, relatively simple messages between aircraft and ground stations via radio or satellite. The protocol, which was designed by ARINC to replace their VHF voice service and deployed in 1978, uses telex formats. SITA later augmented their worldwide ground data network by adding radio stations to provide ACARS service. ACARS today operates in accordance with the Aeronautical Telecommunications Network (ATN) protocol for Air Traffic Control communications and by the Internet Protocol for airline communications. Airspace concept. An airspace concept provides the outline and intended framework of operations within an airspace. Airspace concepts are developed to satisfy explicit strategic objectives such as improved safety, increased air traffic capacity and mitigation of environmental impact etc. Airspace Concepts can include details of the practical organisation of the airspace and its users based on particular CNS/ATM assumptions, e.g. ATS route structure, separation minima, route spacing and obstacle clearance. Air Navigation Service Provider (ANSP). An Air Navigation Service Provider is the organisation that separates aircraft both on the ground and in flight in a dedicated block of airspace on behalf of a state or a number of states. Air Navigation Service Providers are either government departments; state owned companies, or privatised organisations. Almanac. A set of orbit parameters that allows calculation of approximate GNSS satellite positions and velocities. The almanac is used by a GNSS receiver to determine satellite visibility and as an aid during acquisition of GNSS satellite signals. Almanac data. A set of data which is downloaded from each satellite over the course of 12.5 minutes. It contains orbital parameter approximations for all satellites, GNSS to universal standard time (UTC) conversion parameters, and single-frequency ionospheric model parameters. Antipodal satellites. Antipodal satellites are satellites in the same orbit plane separated by 180 in argument of latitude. Anti-spoofing. Denial of the P-code by the control segment is called anti-spoofing. It is normally replaced by encrypted Y-code. ATNS/HO/C09/30/02/01 Page 12 of July 2010

13 Approach Procedure with Vertical guidance (APV). An instrument procedure which utilises lateral and vertical guidance but does not meet the requirements established for precision approach and landing operations. Area Navigation (RNAV). RNAV is a method of navigation that makes possible the operation of an aircraft on any desired flight path within the coverage of station-referenced navigation aids or within the limits of the capability of self-contained aids, or a combination of these. Note: RNAV systems are divided into two different types; The first is the older more common standard system known simply as a RNAV System. The second and more modern type is known as a RNP system. The fundamental difference between the two is that a RNP System is capable of on-board navigation performance monitoring and alerting where as the older standard RNAV system does not have these functions. ATM Community. The aggregate of organisations, agencies or entities that may participate, collaborate and cooperate in the planning, development, use, regulation, operation and maintenance of the ATM system. ATM System. A system that provides ATM through the collaborative integration of humans, information, technology, facilities and services, supported by air and ground- and/or space-based communications, navigation and surveillance. ATS surveillance service. A term used to indicate a service provided directly by means of an ATS surveillance system. ATS surveillance system. A generic term meaning variously, ADS-B, PSR, SSR or any comparable ground-based system that enables the identification of aircraft. Note: A comparable ground-based system is one that has been demonstrated, by comparative assessment or other methodology, to have a level of safety and performance equal to or better than monopulse SSR. Baro-VNAV. A navigation system that presents to the pilot computed vertical guidance referenced to a specified vertical path angle (VPA), nominally 3. The computer-resolved vertical guidance is based on barometric altitude and is specified as a VPA from reference datum height (RDH). Base Station. A GNSS receiver that is employed as the stationary reference. It has a known position and transmits messages for the rover receiver to use to calculate its position. Broadcast Ephemerides. A set of parameters which describes the location of satellites with respect to time, and which is transmitted (broadcast) from satellites. Canada-Wide Differential Global Positioning System (CDGPS). The CDGPS is a free DGPS service that is accessible coast-to-coast, throughout most of the continental United States, and into the Arctic. ATNS/HO/C09/30/02/01 Page 13 of July 2010

14 Coarse Acquisition (C/A) code. A pseudo-random string of bits that is used primarily by commercial GNSS receivers to determine the range to the transmitting GNSS satellite. The 1023 chip GPS C/A code repeats every 1 mili-second giving a chip length of 300 m, which is very easy to lock onto. Collaborative Decision Making (CDM). In the South African ATM context CDM will be understood as meaning the following; A process of collaboratively considering alternative understandings of a problem, an issue or a topic, whilst recognising competing interests, priorities or constraints. Fundamental to this process is a requirement to articulate in a concise and agreed upon manner the problem, issue or topic. This process is aimed at improving the ATM system through increased information exchange among and brings together the various parties in the ATM community. This process will result in an agreed to application of the most appropriate action. Control Segment. The master control station and the globally dispersed reference stations used to manage the GNSS satellites, determine their precise orbital parameters, and synchronise their clocks. Coordinated Universal Time (UTC). This time system uses the second-defined true angular rotation of the Earth measured as if the Earth rotated about its Conventional Terrestrial Pole. However, UTC is adjusted only in increments of one second. The time zone of UTC is that of Greenwich Mean Time (GMT). Dead Reckoning. The process of determining a vessel s approximate position by applying (DR) from its last known position a vector or a series of consecutive vectors representing the run that has since been made, using only the courses being steered, and the distance run as determined by log, engine rpm, or calculations from speed measurements. Differential GNSS (DGNSS). A technique to improve GNSS accuracy that uses pseudo-range errors at a known location to improve the measurements made by other GNSS receivers within the same general geographic area. Dilution of Precision (DOP). A numerical value expressing the confidence factor of the position solution based on current satellite geometry. The lower the value, the greater the confidence in the solution. DOP can be expressed in the following forms: GDOP: PDOP: HTDOP: HDOP: VDOP: TDOP: Uncertainty of all parameters (latitude, longitude, height, clock offset) Uncertainty of 3-D parameters (latitude, longitude, height) Uncertainty of 2-D and time parameters (latitude, longitude, time) Uncertainty of 2-D parameters (latitude, longitude) Uncertainty of height parameter Uncertainty of clock offset time parameter Doppler. The change in frequency of sound, light, or other wave caused by movement of its source relative to the observer. Theoretical Doppler: The expected Doppler frequency based on a satellite s motion relative to the receiver. It is computed using the satellite s co-ordinates and velocity, and the receiver s co-ordinates and velocity. ATNS/HO/C09/30/02/01 Page 14 of July 2010

15 Apparent Doppler: Same as Theoretical Doppler of satellite above, with clock drift correction added. Instantaneous Carrier: The Doppler frequency measured at the receiver, at the epoch. Earth-Centred-Earth Fixed (ECEF). This is a co-ordinate system which has the X-axis in the Earth s equatorial plane pointing to the Greenwich prime meridian, the S-axis pointing to the North Pole, and the Y-axis in the equatorial plane 90 from the X-axis with an orientation which forms a right-handed XYS system. Ephemeris. A set of satellite orbit parameters that are used by a GNSS receiver to calculate precise GNSS satellite positions and velocities. The ephemeris is used in the determination of the navigation solution and is updated periodically by the satellite to maintain the accuracy of GNSS receivers. Ephemeris data. The data down-linked by a GNSS satellite describing its own orbital position with respect to time. Epoch. Strictly a specific point in time. Typically when an observation is made. Fault Detection and Exclusion (FDE). Fault detection and exclusion is a function performed by some GNSS receivers. This function is designed to detect the presence of a faulty satellite signal and to then exclude it from the position calculation. Flight Management System (FMS). An integrated system consisting of an airborne sensor, receiver and computer with both navigation and aircraft performance databases, which provides aircraft performance and RNAV guidance to a display and automatic flight control system (autopilot). Flight Technical Error (FTE). The accuracy with which an aircraft is controlled, as measured by the indicated aircraft position with respect to the indicated command or desired position. It does not include blunder errors. Note: FTE is sometimes referred to as path steering error (PSE). Fixed Radius Path (FRP). A fixed radius path is a type of RNAV System Leg. Fixed radius paths take two forms, the radius to fix (RF) and the fixed radius transition (FRT). These FRPs legs are used in en-route and terminal procedure design to increase the capacity of a specific portion of airspace. ATNS/HO/C09/30/02/01 Page 15 of July 2010

16 Fixed Radius Transition (FRT). The fixed radius transition leg may be employed when there is a requirement for a curved path to be used during en-route procedure design. The FRT leg is defined by radius, arc length and a fix. RNP systems capable of flying this leg type, are also capable of conforming to the same trackkeeping accuracy during the turn as in a straight line segments in accordance with the navigation specification published for the portion of airspace within which this manoeuvre is required. Bank angle limits for different aircraft types and winds aloft are taken into account in procedure design. This turn has two possible radii, 22.5 NM for high altitude routes (above FL195) and 15 NM for low altitude routes. Using such path elements in a RNAV route enables improvement in airspace usage through more efficient and reduced spacing between parallel routes. Flexible Use of Airspace (FUA). Within the context of this document, FUA is understood to mean; Airspace is no longer designated as purely "civil" or "military" airspace, but considered as one continuum and allocated according to user requirements. This allocation will done by the ANSP and in accordance with an agreed to CDM process. Any necessary airspace segregation is temporary and based on real-time usage within a specific time period. Contiguous volumes of airspace are not constrained by national boundaries. Flight profile. The flight path of an aircraft expressed in terms of altitude, speed, range, time and manoeuvre. Galileo. Galileo will be the European Union s own global navigation satellite system, providing a highly accurate, guaranteed global positioning service under civilian control. The fully deployed Galileo system will consist of 30 satellites (27 operational + 3 active spares), positioned in three circular orbits, km above the Earth, and at an inclination of the orbital planes of 56 with reference to the equatorial plane. Gate to Gate. A concept where the air traffic operations of ATM community members are such that the successive planning and operational phases of their processes are managed and can be achieved in a seamless and coherent manner. Geocentric. Relating to, measured from, or with respect to the centre of mass of the Earth. Geodetic System. Geodetic systems or geodetic data are used in geodesy, navigation, surveying by cartographers and satellite navigation systems to translate positions calculated in terms of X, Y and S coordinate models into conventional latitude and longitude position. Ground-Based Augmentation System (GBAS). A ground-based augmentation system is a system that supports wide-area or regional augmentation through the use of additional satellite-broadcast messages. Such systems are commonly composed of multiple ground stations, located at accuratelysurveyed points. The ground stations take measurements from one or more of the GNSS satellites, the satellite signals, or other environmental factors which may impact the signal received by the users. Using these measurements, information messages are created and sent to one or more satellites for broadcast to the end users. Generally, GBAS networks are considered localised, supporting receivers within 20km, and transmitting in the very high frequency (VHF) or ultra high frequency (UHF) bands. ATNS/HO/C09/30/02/01 Page 16 of July 2010

17 Geo-stationary. A satellite orbit along the equator that results in a constant fixed position over a particular reference point on the Earth s surface. Global Navigation Satellite System (GLONASS). GLONASS is a radio satellite navigation system, the Russian counterpart to the United States GPS and European Union s Galileo positioning systems. When complete, the GLONASS space segment will consist of 24 satellites in 3 orbital planes, with eight satellites per plane. The satellites are placed into nominally circular orbits with target inclinations of 64.8 and an orbital height of about km, which is about km lower than GPS satellites. Global Navigation Satellite Systems (GNSS). GNSS is the standard generic term for satellite navigation systems (Sat Nav) that provide autonomous geo-spatial positioning with global coverage. GNSS allows small electronic receivers to determine their location (longitude, latitude, and certain receivers also altitude) to within a few meters using time signals transmitted along a line-of-sight by radio from satellites. Receivers calculate the precise time as well as their position, which can be used as a reference in navigation computers. The Global Positioning System (GPS) is a space-based global navigation satellite system that provides reliable location and time information in all weather and at all times and anywhere on or near the Earth where there is an unobstructed line of sight to four or more GPS satellites. It is maintained by the United States government and is freely accessible by anyone with a GPS receiver. Ground-Based Regional Augmentation System (GRAS). Each of the terms, ground-based augmentation system (GBAS) and ground-based regional augmentation system (GRAS) describe a system that supports augmentation through the use of terrestrial radio messages. As with the satellite based augmentation systems, ground-based augmentation systems are commonly composed of one or more accurately surveyed ground stations, which take measurements concerning the GNSS, and one or more radio transmitters, which transmit the information directly to the end user. GRAS is applied to systems that support a larger (more than 20km), regional area, and transmit in the VHF bands. INMARSAT. INMARSAT plc. is a British satellite telecommunications company, offering global, mobile services. It provides telephony and data services to users worldwide, via portable or mobile terminals which communicate to ground stations through eleven geosynchronous telecommunications satellites. Inmarsat's network provides communications services to a range of governments, aid agencies, media outlets and businesses with a need to communicate in remote regions or where there is no reliable terrestrial network. An Inertial Navigation System (INS) is a navigation aid that uses a computer, motion sensors (accelerometers) and rotation sensors (gyroscopes) to continuously calculate via dead reckoning the position, orientation, and velocity (direction and speed of movement) of a moving object without the need for external references. It is used on vehicles such as ships, aircraft, submarines, guided missiles, and spacecraft. Other terms used to refer to inertial navigation systems or closely related devices include inertial guidance system, inertial reference platform, inertial instrument, and many other variations. ATNS/HO/C09/30/02/01 Page 17 of July 2010

18 Lateral Navigation (LNAV). LNAV refers to navigating over a ground track with guidance from an electronic device which gives the pilot (or autopilot) error indications in the lateral plane only and not in the vertical plane. In aviation lateral navigation is one of two guidance types: linear guidance and angular guidance. Linear guidance means that the actual position of the aircraft, i.e. the deviation left or right of the desired ground track is available as a distance. In angular guidance, the error indication is given in degrees of arc from the desired line relative to a ground-based navigation device. To provide an illustration, as the aircraft approaches the ground-based navigation device whilst maintaining a constant angular error, the aircrafts distance from the desired ground line decreases. In the context of aviation instrument approaches, an LNAV approach (one that uses lateral navigation) is implied to be a approach using GNSS as the primary navigation source and to have linear lateral guidance. A VOR based approach will have angular lateral guidance. The FMS mode is normally called LNAV or Lateral Navigation for the lateral flight plan. LNAV provides roll steering command to the autopilot and VNAV provides speed and pitch or altitude targets. L-band. L-band is a frequency range between 390 MHz and 1.55 GHz which is used for satellite communications and for terrestrial communications between satellite equipment. L-band includes GNSS carrier frequencies L1, L2, CDGPS and the Omni-STAR satellite broadcast signal. Minimum Navigation Performance Specification (MNPS). A specified set of minimum navigation performance standards which aircraft must meet in order to operate in MNPS designated airspace. In addition, aircraft must be certified by their State of Registry for MNPS operation. The objective of MNPS is to ensure the safe separation of aircraft and to derive maximum benefit, generally through reduced separation standards, from the improvement in accuracy of navigation equipment developed in the recent years. Mixed navigation environment. An environment where different navigation specifications may be applied within the same airspace (e.g. RNP 10 routes and RNP 4 routes in the same airspace) or where operations using conventional navigation are allowed in the same airspace with RNAV or RNP applications. Multipath Errors. GNSS positioning errors caused by the intersection of the satellite signal and its reflections. Nanosecond. 1 x 10-9 second. Navigation aid (NAVAID) infrastructure. NAVAID infrastructure refers to space-based and/or ground-based navigation aids available to meet the requirements in the navigation specification. Navigation application. The application of a navigation specification and the supporting NAVAID infrastructure, to routes, procedures, and/or defined airspace volume, in accordance with the intended airspace concept. Note: The navigation application is one element, along with communication, surveillance and ATM procedures which meet the strategic objectives in a defined airspace concept. ATNS/HO/C09/30/02/01 Page 18 of July 2010

19 Navigation function. The detailed capability of a navigation system (such as the execution of leg transitions, parallel offset capabilities, holding patterns, navigation databases) required to meet an airspace concept requirement. Note: Navigational functional requirements are one of the drivers for the selection of a particular navigation specification. Navigation functionalities (functional requirements) for each navigation specification can be found in Volume II, Parts B and C of the Performance-Based Navigation (PBN) Manual (Doc 9613). Navigation specification. A set of aircraft and aircrew requirements needed to support Performance-Based Navigation operations within a defined airspace. There are two kinds of navigation specification: RNAV specification. A navigation specification based on area navigation that does not include the requirement for performance monitoring and alerting, designated by the prefix RNAV, e.g. RNAV 5, RNAV 1 and RNP specification. A navigation specification based on area navigation that includes the requirement for performance monitoring and alerting, designated by the prefix RNP, e.g. RNP 4, RNP APCH. Note: The Performance-Based Navigation (PBN) Manual (Doc 9613), Volume II, contains detailed guidance on navigation specifications. Navigation System Error (NSE). This is the root-sum-square (RSS) of the ground station error contribution, the airborne receiver error and the display system contribution. Note: NSE is sometimes referred to as position estimation error (PEE). Non-Precision Approach. An instrument approach procedure which utilises lateral guidance but does not utilise vertical guidance. Note: Lateral and vertical guidance refers to the guidance provided either by a groundbased navigation aid or computer-generated navigation data. Oblate Spheroid. If an ellipse is rotated about its minor axis, the result is an oblate (flattened) spheroid, like a lentil. Omni-STAR. A wide-area GNSS correction service, using L-band satellite broadcast frequencies ( MHz). Data from many widely-spaced Reference Stations is used in a proprietary multisite solution. Omni-STAR Virtual Base Station types achieve sub-metre positioning over most land areas worldwide while Omni-STAR High Performance (HP) types achieve 10 cm accuracy. Use of the Omni-STAR service requires a subscription. Path Definition Error (PDE). The distance between the defined path and the desired path at a specific point and time. ATNS/HO/C09/30/02/01 Page 19 of July 2010

20 P-code. Precise code or protected code. A pseudo-random string of bits that is used by GPS receivers to determine the range to the transmitting GPS satellite. P-code is replaced by an encrypted Y-code when anti-spoofing is active. Y-code is intended to be available only to authorised (primarily military) users. Performance-Based Navigation (PBN). Area navigation based on performance requirements for aircraft operating along an ATS route, on an instrument approach procedure or in a designated airspace. Note: Performance requirements are expressed in navigation specifications in terms of accuracy, integrity, continuity, availability and functionality needed for the proposed operation in the context of a particular airspace concept. Perigee. The point in a body s orbit at which it is nearest the Earth. Precise Positioning Service (PPS). The GNSS positioning, velocity, and time service which is available on a continuous, worldwide basis to users authorised by the US Department of Defence (typically using P-code). Procedural control. Air traffic control service provided by using information derived from sources other than an ATS surveillance system. Precision Approach. An instrument approach procedure using precision lateral and vertical guidance with minima as determined by the aircraft approach category. Note: Lateral and vertical guidance refers to the guidance provided either by a groundbased navigation aid or computer-generated navigation data. Pseudo-random Noise Number (PRN#). A number assigned by the GPS system designers to give a set of pseudo-random codes. Typically, a particular satellite will keep its PRN (and hence its code assignment) indefinitely, or at least for a long period of time. It is commonly used as a way to label a particular satellite. Pseudo-range. The calculated range from the GNSS receiver to the satellite determined by taking the difference between the measured satellite transmit time and the receiver time of measurement and multiplying it by the speed of light. This contains several sources of error. Pseudo-range measurements. Measurements made using one of the pseudo-random codes on the GNSS signals. They provide an unambiguous measure of the range to the satellite including the effect of the satellite and user clock biases. PS-90. Parametri Semli 1990 (PS-90, or in English translation, Parameters of the Earth 1990, PE-90) geodetic datum. GLONASS information is referenced to the PS-90 geodetic datum and GLONASS co-ordinates are reconciled in some GLONASS-capable GNSS receivers through a position filter and output to WGS-84. ATNS/HO/C09/30/02/01 Page 20 of July 2010

21 Radius to fix (RF). The radius to fix leg type may be employed when there is a requirement for a curved path to be used during terminal or approach procedure design. The RF leg is defined by radius, arc length and a fix. RNP systems capable of flying this leg type, are also capable of conforming to the same trackkeeping accuracy during the turn as in a straight line segments in accordance with the navigation specification published for the portion of airspace within which this manoeuvre is required. Bank angle limits for different aircraft types and winds aloft are taken into account in procedure design. This turn has two possible radii, 22.5 NM for high altitude routes (above FL195) and 15 NM for low altitude routes. Using such path elements in a RNAV route enables improvement in airspace usage through more efficient and reduced spacing between parallel routes. Receiver Autonomous Integrity Monitoring (RAIM). A form of ABAS whereby a GNSS receiver processor determines the integrity of the GNSS navigation signals using only GPS signals or GPS signals augmented with altitude (baro-aiding). This determination is achieved by a consistency check among redundant pseudo-range measurements. At least one additional satellite needs to be available with the correct geometry over and above that needed for the position estimation, for the receiver to perform the RAIM function. Real-Time Kinematic (RTK). A type of differential positioning based on observations of a carrier phase. Required Navigational Performance (RNP). A statement of the navigation performance necessary for operations within a defined Airspace. RNAV Approach. A generic term used to describe instrument approach procedures that rely on aircraft area navigation equipment (the Flight Navigation Computer - FNC component of the Flight Management System - FMS) for navigation guidance. RNAV approach procedures are designated and utilised as follows; RNAV (GNSS). The current European Non-Precision RNAV instrument approach application. RNAV 1. PBN SIDs and STARs and Instrument Approach Procedures up to the final approach fix. RNAV 2. PBN SIDs and STARs and Instrument Approach Procedures up to the final approach fix. RNP 2. Future development. Basic-RNP 1. PBN SIDs and STARs. Advanced-RNP 1. Future development. RNP APCH. PBN Instrument Approach Procedure and the current RNAV (GNSS) Non-Precision RNAV Instrument Approach Procedures. RNP APCH is defined as a RNP approach procedure that requires a lateral TSE of +/- 1 NM in the initial, intermediate and missed approach segments and a lateral TSE of +/- 0.3 NM in the final approach segment. RNP AR APCH. PBN Instrument Approach Procedure. RNP AR APCH is defined as a RNP approach procedure that requires a lateral TSE as low as +/- 0.1 NM on any segment of the approach procedure. RNP AR APCH procedures also require that a specific vertical accuracy be maintained as detailed in The Performance-Based Navigation (PBN) Manual (Doc 9613), Volume II, Chapter 6. ATNS/HO/C09/30/02/01 Page 21 of July 2010

22 RNAV operations. This refers to aircraft operations where the navigation of the aircraft is achieved using the RNAV method of navigation (in this instance the navigation function is achieved through automated means i.e. the use of a standard RNAV system without the ability to perform on-board navigation performance monitoring and alerting). RNAV Route. An ATS route established for the sole use of aircraft capable of employing RNAV in accordance with a prescribed RNAV navigation specification. RNAV system. This refers to a flight navigation computer that enables the application of the RNAV method of navigation through automated means without the ability to perform on-board navigation performance monitoring and alerting. A RNAV system may be and most often is included as part of a Flight Management System (FMS). RNAV system Leg. The path between two waypoints. RNP operations. This refers to aircraft operations where the navigation of the aircraft is achieved using the RNAV method of navigation (in this instance the navigation function is achieved through automated means i.e. the use of a RNP system and thus includes the ability to perform on-board navigation performance monitoring and alerting). RNP route. An ATS route established for the sole use of aircraft adhering to a prescribed RNP navigation specification. RNP system. This refers to a flight navigation computer that enables the application of the RNAV method of navigation through automated means and thus includes the ability to perform on-board navigation performance monitoring and alerting. RNP systems are only available as integral components of Flight Management Systems (FMS). Rover Station. The GNSS receiver which does not know its positions and needs to receive measurements from a base station to calculate differential GNSS positions (the terms remote and rover are interchangeable). Safety-of-Life (SOL). The safety-of-life service will be offered to Galileo users who are highly dependent on precision, signal quality and signal transmission reliability (typically commercial aviation). It will offer a high level of integrity and consequently, provide the user with a very rapid warning of any possible malfunctions. The SOL service will be transmitted in two frequency bands. On the L1 at MHz and on E5a+E5b at MHz. Users may receive signals from two frequency bands independently. Satellite-Based Augmentation System (SBAS). A wide coverage augmentation system in which the user receives augmentation information from a satellite-based transmitter. Selected Availability (SA). The method used in the past by the US Department of Defence to control access to the full accuracy achievable by civilian GPS equipment (generally by introducing timing and ephemeris errors). Selected Waypoint. The waypoint currently selected to be the point toward which the vessel is travelling. Also called to waypoint, destination or destination waypoint. ATNS/HO/C09/30/02/01 Page 22 of July 2010

23 Sidereal Day. A sidereal day is the rotation of the Earth relative to the equinox and is equal to one calendar day (the mean solar day) minus approximately 4 minutes. Spheroid. A spheroid, or ellipsoid of revolution is a quadric surface obtained by rotating an ellipse about one of its principal axes; in other words, an ellipsoid with two equal semi-diameters. Standard Instrument Arrival (STAR). A designated instrument flight rule arrival route linking a significant point, normally on an ATS route, with a point from which a published instrument approach procedure can be commenced. Standard Instrument Departure (SID). A designated instrument flight rule departure route linking the aerodrome or a specified runway of the aerodrome with a specified significant point, normally on a designated ATS route, at which the en-route phase of a flight commences. Standard Positioning Service (SPS). A positioning service made available by the US Department of Defence which is available to all GPS civilian users on a continuous, worldwide basis (typically using C/A code). Space Vehicle ID (SV). Sometimes used as SVID. A unique number assigned to each satellite for identification purposes. The space vehicle is a GNSS satellite. Total System Error (TSE). The difference between the true position and desired position of an aircraft. This error is equal to the vector sum of the path steering error, path definition error and position estimation error. In the lateral dimension, a combination of navigation system error, RNAV computation error, display system error and FTE. In the longitudinal dimension, a combination of navigation system error, RNAV computation error and display system error. Trajectory. This is a description of the movement of an aircraft, both in the air and on the ground, including position, time and, at least via calculation, speed and acceleration. Vertical Navigation (VNAV). Vertical Navigation in aviation is a function of an autopilot which directs vertical movement of aircraft according to a pre-programmed FMS flight path during cruise, according to the ILS glide slope during a conventional precision approach or more recently according to a preprogrammed FMS flight path during a RNAV approach. Guidance includes control of the pitch axis and control of the throttle. Waypoint. A specified geographical location used to define an ATS route. A waypoint is defined as a geographic coordinate (in WGS84) and is identified either: by a 5 letter unique name code, e.g. BARNA, or if located with a ground-based NAVAID by the 3 letter ICAO identifier for that station, e.g. OTR, or in Terminal Airspace only, by an alphanumeric name code, e.g. DF410. World Geodetic System 1984 (WGS-84). An ellipsoid designed to fit the shape of the entire Earth as well as possible with a single ellipsoid. It is often used as a reference on a worldwide basis, while other ellipsoids are used locally to provide better fit to the Earth in a local region. GNSS uses the centre of the WGS-94 ellipsoid as the centre of the GNSS ECEF reference frame. ATNS/HO/C09/30/02/01 Page 23 of July 2010

24 Y-code. An encrypted form of P-code. Satellites transmit Y-code in place of P-code when antispoofing is in effect. 4D RNAV. 4D RNAV is a concept that has developed as the application of RNAV evolved. This development progressed from 2D RNAV to 3D RNAV to 4D RNAV and may be explained as follows; 2D RNAV encompasses the application of RNAV capabilities in the horizontal plane only; 3D RNAV indicates the addition of a guidance capability in the vertical plane (providing profile guidance) to the 2D RNAV capabilities; and 4D RNAV indicates the addition of a time function (giving time guidance) to 3D RNAV capabilities. 4D Trajectory. A four-dimensional (x, y, z and time) trajectory of an aircraft from gate-to-gate, at the level of fidelity required for attaining the agreed ATM System performance levels. ATNS/HO/C09/30/02/01 Page 24 of July 2010

25 1 AREA NAVIGATION (RNAV) SYSTEMS. 1.1 Background The ability to navigate an aircraft has been a fundamental component of flying from the day the Wright Brothers made their first flight. Since that first powered flight, flying and navigating aircraft has developed exponentially. This chapter will discuss the development of this near mythical thing termed aircraft navigation, aka area navigation. The first few flights ever undertaken where made during daylight, clear of any cloud and precipitation and with the pilot seeing where he was flying (visual navigation). Very soon the potential of commercial air travel was identified and with this came the realisation that aircraft would have to be flown and thus navigated by night and during adverse weather conditions. This ushered in the concept of all weather operations. Early public transport operation relied on radio beacons, intermittent two way communication with Air Traffic Control (ATC) and a very basic airway infrastructure. The limited level of Air Traffic Service (ATS) was based on what we now know as procedural control, requiring and limiting aircraft to fly either directly to or away from beacons (VOR or NDB ground stations). Very soon after the start of public air transport operations, aircraft were being operated, but for takeoff and landing, entirely without visual reference to the ground. Navigation was effected by sole reference to radio beacons and this process came to be known as Radio Navigation. Radio Navigation enabled the early navigators to manually plot the aircraft position, calculate ground speed and estimated time of arrival and plot a required course to any point on their maps. This new technique was called Area Navigation and was based on Radio Navigation. Soon these two concepts became synonymous one with the other and were simply referred to as RNAV. The accepted meaning of the abbreviation RNAV being Area Navigation. Advances in technology meant that the navigation function could be performed by a purpose built Flight Navigation Computer (FNC). The FNC would eventually be incorporated into the aircraft systems management computer know as the Flight Management System (FMS), thus replacing the human flight navigator. The continuing growth in aviation increased the demands on airspace capacity and therefore emphasised the need for optimum utilisation of available airspace. Improved operational efficiency derived from the application of RNAV techniques resulted in the development of navigation applications in various regions worldwide and for all phases of flight. Requirements for RNAV applications on specific routes and/or within specific airspaces where defined. This was an attempt to ensure that flight crews and air traffic controllers (ATCs) were aware of the on-board RNAV system capabilities. This was not entirely successful and largely failed to achieve the anticipated financial benefits of RNAV as was initially identified. RNAV systems evolved in a manner similar to but much faster than conventional ground-based routes and procedures. Air Navigation Service Providers (ANSPs) and Civil Aviation Authorities would identify a specific RNAV system, its performance would be evaluated through a combination of analysis and flight testing and then it would be approved for a specific procedure in a specific portion of airspace. For domestic operations, the initial RNAV systems used very high frequency omnidirectional radio range (VOR) and distance measuring equipment (DME) for estimating their position; for oceanic operations, Inertial Navigation Systems (INS) were employed. These new systems were developed, evaluated and certified. Airspace and obstacle clearance criteria were developed based on the performance of available equipment and specifications for requirements were based on available capabilities. In some cases, it was necessary to identify the individual models of equipment that could be operated within the airspace concerned. Such prescriptive requirements resulted in delays to the introduction of new RNAV system capabilities and higher costs for maintaining appropriate certification. To avoid such prescriptive specifications of requirements, the Performance-Based Navigation (PBN) Implementation Manual introduces an ATNS/HO/C09/30/02/01 Page 25 of July 2010

26 alternative method for defining equipage requirements by specifying the navigation performance requirements Conventional Navigation Methods and Procedures This new concept of all weather operations meant that some means of navigation at night and during adverse weather condition had to be developed, i.e. navigating without any visual reference to the ground whatsoever. The earliest developments resulted in the wide spread application of what we now refer to as ground-based navigation aids (NAVAIDs VORs & NDBs). These ground-based NAVAIDs would prove to be plagued with limitations, some of these are briefly reviewed below. a. NAVAIDs. Early radio navigation (area navigation aka RNAV) was accomplished with reference to either radio beacons (NDBs, VORs and DMEs) on the ground or on-board self-contained systems (Inertial Navigation Systems - INS). The ground-based NAVAIDs had to have airborne counterparts, these are named as follows; Ground-Based NAVAID VOR DME NDB Airborne Counterpart VOR DME ADF i. Accuracy. Conventional NAVAIDs suffers from various errors, the NDB for instance suffers from a number of errors mostly related to atmospheric conditions. The VOR is less susceptible to these errors but is still restricted to line of sight. Both the NDB and VOR have the further disadvantage of radiation accuracy issues, in that any errors introduced at the station will be magnified with increased distance away from the station. The single most significant error associated with the NDB and VOR may be termed splay errors. This describes the inherent area of uncertainty that results from the inaccurate radial definition by a VOR station or in the case of an NDB/ADF, the inaccurate determination of the bearing to the NDB. The DME is more accurate than both the NDB and VOR in terms of signal (position line) definition in that it does not suffer from this inherent splay error but due to the operating method a DME station is limited to supporting distance calculation by a maximum of 100 airborne DME platforms at any one time (the 100 strongest interrogations rather than the 100 closest aircraft). Due to its inherent limitations, susceptibility to interference and inaccurate bearing definition capability the NDB/ADF was eliminated very early on as a possible navigation ATNS/HO/C09/30/02/01 Page 26 of July 2010

27 signal input to any FNC (now referred to as RANV system). To date multiple simultaneous DME signal inputs to RNAV systems provide the most accurate and cost effective navigation solution where high accuracy is required from RNAV systems. ii. Range. Older NDBs had very limited range while some marine beacons and more modern NDBs are more powerful. VOR stations may be received at distances as great a 200 NM but at this distance the lateral accuracy due to the increasing splay error effect is much reduced. DME stations may be used at distances as large as 200 NM and will maintain their accuracy at maximum range (i.e. DME range arc definition accuracy). b. Displays. DME ADF ADF VOR i. Accuracy Conventional NAVAID displays all suffer from mechanical errors. These were all analogue systems that were linked to mechanical display unit. Due to this fact these displays suffered from a significant display error. Later DME display units had a digital display that practically eliminated any display error. With the development of the glass cockpit the display errors of the VOR were also greatly reduced. ATNS/HO/C09/30/02/01 Page 27 of July 2010

28 c. Plotting Initially a flight navigator would perform a manual plot using the signals from radio beacons. These bearings (to an NDB), radials (from a VOR) and DME range arcs (from a DME ground station) would be plotted. This process, though not necessarily difficult but rather mundane and repetitive, was prone to errors. Lack of attention to detail by the navigator would result in an inaccurate plot and thus the aircraft may be allowed to drift significantly far off course before an effective correction was made. Again as a result of increased operation demand and advances in technology this manual plotting function would ultimately be performed by a FNC. The FNC was able to ensure a repeatable plotting performance, both in terms of accuracy and reliability. Early FNCs were not certified in any way but later application of RNAV saw the introduction of Required Navigation Performance (RNP) accuracy as an attempt to standardise and guarantee the accuracy and repeatability of accurate navigation performance. i. Position Fixing The fundamental aim of navigation is to accurately, reliably and consistently determine and/or know the position of an aircraft in flight. Using navigation signal inputs (NDB, VOR, DME and GNSS) the accuracy of the plotting solution is largely determined by the geometry of the plot. Two position lines (each with an accepted definition accuracy of 5 - the ICAO standard for the VOR) will produce a fairly well defined position. If the same two position line intersected at a smaller angle, the position will be less well defined. This position definition will reduce in clarity as the intersecting angle of the two position lines reduces. ATNS/HO/C09/30/02/01 Page 28 of July 2010

29 1.1.2 RNAV Navigation Methods and Procedures a. Manual Area Navigation (RNAV). The process performed by a flight navigator whereby the manual tuning of VOR, DME and ADF frequencies, physical drawing of position lines from ground-based radio beacons on a plotting chart is carried out, may be termed manual area navigation. This process enables the navigation of an aircraft along any desired/required track within the coverage area of the selected and tuned-in navigation radio beacons. The accuracy of this process is affected by a number of factors and these include but are not limited to the radio beacon signal definition accuracy and the accuracy of the manual plotting by the navigator. The basic process of manual plotting is a fairly laborious process and thus will have a limit in terms of its applicability with an increase in either aircraft speed and/or complexity of route. b. Automated Area Navigation (RNAV). This is where the navigation function (plotting to determine aircraft position) is performed by a FNC. The navigation solution i.e. the aircraft position, is presented to the pilot on either/or both the CDI/(E)HSI and the Primary Navigation Display. The accuracy of this process is affected by the radio beacon signal definition accuracy but the possible error introduced by the human skill factor is removed. Here the processing method of the FNC does have a small influence on the overall navigation accuracy while the impact of aircraft speed and route complexity has been mitigated. In the most recent applications of RNAV it has been found that the processing method of different FNCs result in differing navigation performances in terms of track keeping during turns. This will be discussed later under the headings of Fixed Radius Transitions (FRTs) and Radius to Fix (RF) RNAV system leg types. Automated RNAV or RNAV Systems today use any one or combination of navigation signal inputs. These are DME/DME, VOR/DME, INS and more recently GNSS WGS - 84 Geodetic Reference Datum The Earth is not a perfect sphere, it is now believed that the Earth looks more like an egg rather than a ball. This odd shape was discovered due to the ongoing geographic surveys conducted globally. Historically a number of different means and approaches have been used during these surveys. The World Geodetic System (WGS) is a standard survey reference method (mathematical model of the Earth) for use in cartography, geodesy, and navigation. It comprises a standard coordinate frame for the Earth, a standard spheroidal reference surface (the datum or reference ellipsoid) for raw altitude data, and a gravitational equipotential surface (the geoid) that defines the nominal sea level. Because of the combined effects of gravitation and rotation, the Earth's shape is roughly that of a sphere slightly flattened at the poles. For that reason, in cartography the shape of the ATNS/HO/C09/30/02/01 Page 29 of July 2010

30 Earth is often approximated by an oblate spheroid instead of a sphere. The current World Geodetic System model, in particular, uses a spheroid whose radius is approximately 6, km at the equator and 6, km at the poles (a difference of over 21 km). The latest revision is WGS 84 (dating from 1984 and last revised in 2004), which will be valid up to about Earlier schemes included WGS 72, WGS 66, and WGS 60. WGS 84 is the reference coordinate system used by the Global Positioning System. The coordinate origin of WGS 84 is located at the Earth's centre of mass; the error is believed to be less than 2 cm. In WGS 84, the meridian of zero longitude is the International Earth Rotation and Reference Systems Service (IERS) Reference Meridian. It lies 5.31 arc seconds east of the Greenwich Prime Meridian, which corresponds to meters (336.3 feet) at the latitude of the Royal Observatory. As of the latest revision, the WGS 84 datum surface is a pole-flattened (oblate) spheroid, with major (transverse) radius a = 6,378,137 m at the equator, and minor (conjugate) radius b = 6,356,752 m at the poles (a flattening of km, or 1/ % in relative terms). The b parameter is often rounded to 6,356,752.3 m in practical applications. The 1980 Geodetic Reference System (GRS80) posted a 6,378,137 m semi-major axis and a 1: flattening. This system was adopted at the XVII General Assembly of the International Union of Geodesy and Geophysics (IUGG). It is essentially the basis for geodetic positioning by the Global Positioning System and is thus also in extremely widespread use outside the geodetic community. Presently WGS 84 uses the 1996 Earth Gravitational Model (EGM96) geoid, revised in The deviations of the EGM96 geoid from the WGS 84 reference ellipsoid range from about m to about +85 m. EGM96 differs from the original WGS 84 geoid, referred to as EGM84. In the early 1980s the need for a new world geodetic system was generally recognised by the geodetic community, also within the US Department of Defence. WGS 72 no longer provided sufficient data, information, geographic coverage, or product accuracy for all the then current and anticipated applications. The means for producing a new WGS were available in the form of improved data, increased data coverage, new data types and improved surveying techniques. GRS 80 parameters together with available Doppler, satellite laser ranging and Very Long Baseline Interferometry (VLBI) observations constituted significant new information. An outstanding new source of data had become available from satellite radar altimetry. Also available was an advanced least squares method called collocation which allowed for a consistent combination solution from different types of measurements all relative to the Earth's gravity field, i.e. geoid, gravity anomalies, deflections, dynamic Doppler, etc. The WGS 84 originally used the GRS 80 reference ellipsoid, but has undergone some minor refinements in later editions since its initial publication. Most of these refinements are important for high-precision orbital calculations for satellites but have little practical effect on typical topographical uses. The new World Geodetic System was called WGS 84. It is currently the reference system being used by the Global Positioning System. It is geocentric and globally consistent within ±1 m. Current geodetic realisations of the geocentric reference system family International Terrestrial Reference System (ITRS) maintained by the IERS are geocentric, and internally consistent, at the few-cm level, while still being meter-level consistent with WGS Historical Overview Future Air Navigation System (FANS) Air Traffic Control's ability to monitor aircraft has always been outpaced by the growth of flight as a mode of travel. In an effort to improve aviation communication, navigation, surveillance, (CNS) and air traffic management (ATM) the International Civil Aviation Organisation (ICAO) ATNS/HO/C09/30/02/01 Page 30 of July 2010

31 developed standards for a future integrated system, this system was termed the Future Air Navigation System (FANS) and would allow controllers to play a more passive monitoring role through the use of increased automation and the wider application of RNAV operations with increased reliance on satellite based navigation. Today the world's Air Traffic Control (ATC) system still uses components defined in the 1940s following the 1944 meeting in Chicago which launched the creation of the ICAO. This traditional ATC system uses analogue radio systems for aircraft Communications, Navigation & Surveillance (CNS). In 1983, THE ICAO established the special committee on the Future Air Navigation System (FANS), charged with developing the operational concepts for the future of Air Traffic Management (ATM). The FANS report was published in 1988 and laid the basis for the industry's future strategy for ATM through digital CNS using satellites and data links. Work then started on the development of the technical standards needed to realise the FANS Concept. In the early 1990s, the Boeing Company announced a first generation FANS product known as FANS-1. Prior to this the international ATC system was not designed to fully take advantage of flight deck capabilities. The FANS-1 package was based on the early ICAO technical work for Automatic Dependent Surveillance (ADS) and Controller Pilot Data Link Communications (CPDLC), and implemented as a software package on the Flight Management Computer (FMS) of the Boeing It used existing satellite based Aircraft Communications Addressing and Reporting System (ACARS) communications (via Inmarsat Data-2 service) and was targeted at operations in the South Pacific Oceanic region. The deployment of FANS-1 was originally justified by improving route choice and thereby reducing fuel burn. The Data link Control and Display Unit (DCDU) on an Airbus A330, the pilot interface for sending and receiving CPDLC messages. A product similar to the FANS-1 package was later developed by Airbus for the A-340 and A- 330 and was known as the FANS-A package. Boeing also extended the range of aircraft supported to include the Boeing 777 and 767. Together, the two products are collectively known as FANS-1/A. The main industry standards describing the operation of the FANS-1/A products are ARINC 622 and EUROCAE ED-100/RTCA DO-258. Both the new Airbus A-380 and Boeing 787 have FANS-1/A capability. The ICAO work continued after FANS-1 was announced, and continued to develop the CNS/ATM concepts and now we are moving forward again with the introduction of Performance-Based Navigation (PBN). ATNS/HO/C09/30/02/01 Page 31 of July 2010

32 1.2 Aircraft Area Navigation (RNAV) Computer System Function Today one may choose from a variety of different types of RNAV equipment, covering a wide range of capability and sophistication. The term flight management systems (FMS) is often used to describe any system which provides some kind of advisory or direct control capability for navigation (lateral and/or vertical), fuel management, route planning, etc. Systems which are described as performance management systems, fuel management systems, flight management control systems and navigation management systems are also available. Throughout this document, FMS is used in a generic sense and is not intended to imply any one specific type of system. Many new public transport and business/executive jet aircraft have a flight management system installation as an integral part of the avionics system, but many older aircraft have been retro-fitted with FMS systems. The core of the FMS is a computer that, as far as lateral navigation is concerned, operates with a large data base which enables many routes to be pre-programmed and fed into the system. In operation, the system is constantly updated with respect to positional accuracy by reference to conventional navigation aids, and the sophisticated data base will ensure that the most appropriate aids are selected and tuned in to automatically. A RNAV system can be viewed as a computer which creates an electronic model of the world and then calculates and expresses the aircraft s position on this model world. In order to accurately place or locate the aircraft s position on this world model, the RNAV system automatically accepts inputs from various sources. These can be ground-based, satellite or airborne navigation aids or systems e.g. VOR, DME, INS or GNSS. 3D position information can be obtained by, for example, use of four or more satellites. Importantly, the quality of the available NAVAID infrastructure directly impacts the accuracy of the navigation solution. Thus a patchy NAVAID environment might result in inconsistent navigation accuracy. The challenge to achieving accurate, reliable, efficient and continued RNAV is the accurate placement of the aircraft on its world model using the available NAVAID infrastructure. However, the high quality of navigation based on RNAV is currently demonstrated world-wide by the large number of aircraft operating using RNAV on conventional routes. As stated earlier, RNAV systems can accept a variety of navigation inputs and these are; VOR/DME, OMEGA/very low frequency (VLF) (no longer functioning), LORAN-C (no longer functioning), Inertial Navigation Systems (INS), DME/DME; and Global Navigation Satellite Systems (GNSS). It is generally assumed that all of the above systems are either coupled or capable of being coupled directly to the auto-flight system (autopilot). This facility may become a prerequisite of future RNAV equipment. ATNS/HO/C09/30/02/01 Page 32 of July 2010

33 RNAV System Capabilities - The following system functions are the minimum required to conduct basic RNAV operations: Continuous indication of aircraft position relative to track to be displayed to the pilot flying on a navigation display situated in his primary field of view. In addition where the minimum flight crew is two pilots, indication of aircraft position relative to track to be displayed to the pilot not flying on a navigation display situated in his primary field of view. Display of distance and bearing to the active (To) waypoint. Display of ground speed or time to the active (To) waypoint. Navigation data storage. Appropriate failure indication of the RNAV system, including the sensors. Pilot interface of a Basic RNAV system using ONLY GNSS input Although one may be able to effectively conduct RNAV operation with a system as stipulated above the ICAO has identified additional functions that it recommends should also be included in RNAV system capabilities. The ICAO recommends that the following system functions and equipment characteristics to be included in RNAV system capability: Autopilot and/or Flight Director coupling. Present position in terms of latitude and longitude. "Direct To" function. Indication of navigation accuracy (e.g. quality factor). Automatic channel selection of radio navigation aids. Navigation data base. Automatic leg sequencing and associated turn anticipation. ATNS/HO/C09/30/02/01 Page 33 of July 2010

34 1.2.1 Navigation The FNC computes data including aircraft position, velocity, track angle, vertical flight path angle, drift angle, magnetic variation, barometric-corrected altitude, estimated time of arrival and wind direction and magnitude. It may also perform automatic radio NAVAID tuning as well as support manual tuning. While navigation can be based upon a single navigation signal source (e.g. GNSS), most systems today are multisensory RNAV systems. Such systems use a variety of navigation sensors including GNSS, DME, VOR and IRS to compute the position and velocity of the aircraft. While the implementation may vary, the system will typically base its calculations on the most accurate positioning sensor available. The RNAV system will confirm the validity of the individual sensor data and, in most systems, will also confirm the consistency of the various sets of data before they are used. GNSS data are usually subjected to rigorous integrity and accuracy checks prior to being accepted for navigation position and velocity computation. DME and VOR data are typically subjected to a series of reasonableness checks prior to being accepted for FNC radio updating. This difference in rigour is due to the capabilities and features designed into the navigation sensor technology and equipment. For multi-sensor RNAV systems, if GNSS is not available for calculating position/velocity, then the system may automatically select a lower priority update mode such as DME/DME or VOR/DME. If these radio update modes are not available or have been deselected, then the system may automatically revert to inertial coasting (i.e. navigation with reference to INS information). For single-sensor systems, sensor failure may lead to a dead reckoning mode of operation. As the aircraft progresses along its flight path, if the RNAV system is using ground NAVAIDs, it uses its current estimate of the aircraft's position and its internal database to automatically tune the ground stations in order to obtain the most accurate radio position. Lateral and vertical guidance is made available to the pilot either on the RNAV system display itself or supplied to other display instruments. In many cases, the guidance is also supplied to an automatic flight guidance system. In its most advanced form, this display consists of an electronic map with an aircraft symbol, planned flight path, and ground facilities of interest, such as NAVAIDs and airports. ATNS/HO/C09/30/02/01 Page 34 of July 2010

35 Area Navigation enables the aircraft to fly a path, or 'leg', between points, called 'waypoints', which are not necessarily co-located with ground-based navigational aids. If a navigation data base is included in the RNAV system capabilities then the data in the database is specific to an Aircraft Operator's (AO's) requirements. This data is taken from the States Aeronautical Information Publications (AIPs) in the form of route structures, operational procedures and Navigation Aids (NAVAIDs). The intended flight path is programmed into the FNC (RNAV system) by the pilot and this is achieved by selecting or inputting a series of waypoints using the RNAV Control Unit. The RNAV system defines the required flight path by linking the waypoints together. It uses the database (if fitted) to call up details of the waypoints to do this. With no database the pilot must insert all waypoint data. The intended flight path is then displayed to the pilot on a Navigation Display (ND). Simple RNAV systems will display the lateral deviation from the required track. If a map display is available the RNAV system will display the intended flight path on this map display. The aircraft s position is calculated using navigation signal inputs. These navigation signal inputs into the FNC (RNAV system) are received via on-board navigation sensors from either ground-based (DME or VOR), space-based (GNSS) NAVAIDs or from on-board inertial platforms (INS). The coordinates of ground-based NAVAIDs are taken from the navigation database (if fitted). The accuracy and consistency of the aircraft's ability to fly the desired path is subject to the aircraft capabilities and on-board functionalities Navigation Database Not all RNAV systems have a navigation database. Where a RNAV system has a navigation database, this data base will store all the uploaded waypoints, path terminators and coordinates for all ground-based NAVAIDs as required by that particular Aircraft Operator (AO). The uploading of this information is done in accordance with a comprehensive laid down procedure. The ICAO requires each State to publish its ATS routes, NAVAID information, aerodrome and related procedures in the AIP (all this information to be in accordance with an agreed to survey process and standard, WGS-84 at the moment). AOs employ third party companies known as 'data houses' to compile specific information from each State to support the AOs individual requirement (this normally relates to the AOs route structure and usual destinations). These data houses produce the datasets using the States AIP as the primary source of information. These data sets are then packaged and ATNS/HO/C09/30/02/01 Page 35 of July 2010

36 shipped in ARINC 424 format to the Original Equipment (RNAV system) Manufacturers (OEMs). The OEMs are known as 'data packers' and they then code and then upload the datasets into the appropriate (target) RNAV systems. The data bases are updated and validated in accordance with the ICAO AIRAC cycle. There are several manufacturers of RNAV systems and the formats used by these systems are different. Furthermore, no two AOs will require exactly the same information. Some AOs will create company routes (a pre-defined series of waypoints) to enable quicker uploads of specific routes. If the data in the dataset is incorrect, the data in the database will be incorrect and the pilot may not be aware of this. Good airmanship dictates that the flight path extracted from the database be checked for accuracy and consistency against the chart information before and during operation. When using a RNAV system with a database, the pilot will select the company route or the waypoints defining the flight planned route in turn from the database to create a route in the FNC (RNAV system). The pilot is unable to change the navigation data in the database. This is a system design characteristic built into the system to avoid risk of data corruption in the uploaded dataset. Most RNAV systems available today include the ability to access a navigation database containing the waypoints, routes, speeds and altitudes for published instrument flight procedures. For RNAV systems without a database, the pilot is required to manually insert the waypoints (key in the coordinates of each waypoint required to define the route). Systems with this functionality will be limited in the navigation specifications that the aircraft can meet. ATNS/HO/C09/30/02/01 Page 36 of July 2010

37 1.2.3 Flight Planning The flight planning function creates and assembles the lateral and vertical flight plan used by the guidance function. A key aspect of the flight plan is the specification of flight plan waypoints using latitude and longitude, without reference to the location of any ground navigation aids. More advanced RNAV systems include a capability for performance management where aerodynamic and propulsion models are used to compute vertical flight profiles matched to the aircraft and able to satisfy the constraints imposed by air traffic control. A performance management function can be complex, utilising fuel flow, total fuel, flap position, engine data and limits, altitude, airspeed, Mach, temperature, vertical speed, progress along the flight plan and pilot inputs. RNAV systems routinely provide flight progress information for the waypoints en-route, for terminal and approach procedures, and the origin and destination. The information includes estimated time of arrival, and distance-to-go which are both useful in tactical and planning coordination with ATC Manual or automated notification of an aircraft s qualification to operate along an ATS route, on a procedure or in a particular portion of airspace is provided to ATC via the Flight Plan. Flight Plan procedures are addressed in Procedures for Air Navigation Services Air Traffic Management (PANS-ATM) (Doc 4444) Guidance and Control A RNAV system provides lateral guidance, and in many cases, vertical guidance as well. The lateral guidance function compares the aircraft s position generated by the navigation function with the desired lateral flight path and then generates steering commands used to fly the aircraft along the desired path. Geodesic or great circle paths joining the flight plan waypoints, typically known as legs, and circular transition arcs between these legs are calculated by the RNAV system. The flight path error is computed by comparing the aircraft s present position and direction with the reference path. Roll steering commands to track the reference path are based upon the path error. These steering commands are output to a flight guidance system, which either controls the aircraft directly or generates commands for the flight director. The vertical guidance function, where included, is used to control the aircraft along the vertical profile within constraints imposed by the flight plan. The outputs of the vertical guidance function are typically pitch commands to a display and/or flight guidance system, and thrust or speed commands to displays and/or an auto-thrust function. The difference between the required (ATS defined) and defined (RNAV system) paths, and especially the ability to follow required (ATS Defined) fixed path turns, depend on but is not limited to: the accuracy of the initial AIP navigation data as supplied by the State, the coding accuracy of the dataset by the data packers, the accuracy and quality of the navigation signals inputs, the accuracy of the on-board navigation sensors, the capabilities, functionalities and processing methodology of the RNAV system, and/or, the manual/flight Director/autopilot control accuracy of the aircraft. ATNS/HO/C09/30/02/01 Page 37 of July 2010

38 1.2.5 Display and System Control Display and system controls provide the means for system initialisation, flight planning, path deviations, progress monitoring, active guidance control and presentation of navigation data for flight crew situational awareness. Garmin 530 RNAV system using GNSS, VOR, DME and ILS input. Garmin 430 RNAV system using GNSS, VOR, DME and ILS input. FMS Primary Navigation Display In complex RNAV systems control is via FMS key pad and in basic systems via the CDU Manual Radio Position Updating In older RNAV systems the INS position is programmed in by a flight crew member, this takes time and is vulnerable to input errors. This position update is normally done during or just prior to engine start-up. The INS position may also require manual position updating by a crew member and if so, this type of system is limited in its application Automatic Radio Position Updating More modern systems will update the INS position automatically using aircraft position entered into the FMS by the crew during FMS initialisation, by conventional NAVAIDs, GBAS or GRAS. ATNS/HO/C09/30/02/01 Page 38 of July 2010

39 1.3 Area Navigation (RNAV) Operations In South Africa RNAV operations have been successfully implemented for the en-route phase of flight between the three major city pairs as well as between Johannesburg and the major coastal cities. We are now at the start of the process to expand this RNAV application into the TMAs and the PBN implementation project will be the vehicle that will enable this expansion RNAV Routes Volume II of the PBN Manual addresses the different Navigation Specifications which are suited to one or more phases of flight. a. EN-ROUTE: Oceanic/Remote Continental Continental b. TERMINAL AIRSPACE: Arrival/Departures Approach: o standard (RNP APCH) with or without vertical guidance, which everyone can fly, or o demanding (RNP AR APCH) requiring specific approval, functionality and training. ATNS/HO/C09/30/02/01 Page 39 of July 2010

40 1.3.2 RNAV Waypoint types The ICAO definition of a Waypoint: A specified geographical location used to define an area navigation route or the flight path of an aircraft employing area navigation. A waypoint is defined as a geographic coordinate (in WGS84) and is identified as follows; by a five letter unique name code, e.g. BARNA, or by a three letter unique name code if located with a ground-based NAVAID using the three letter ICAO identifier for that station, e.g. OTR, or by a alphanumeric name code if used in Terminal Airspace only, DF410. There are several different ways aircraft will fly to, from and between waypoints. As far as procedure execution is concerned, the RNAV system will fly procedures in a consistent manner, regardless of phase of flight, i.e. en-route or terminal. What will be noteworthy is the fact that different RNAV systems and aircraft types will fly the same procedure in a slightly different manner. These differences are due to small variations in the individual RNAV systems analogue as well as individual aircraft flight performances. The way in which an aircraft will fly a particular RNAV SID or STAR depends on the waypoint types and leg types used to define the procedure. RNAV leg types will be discussed under paragraph 1.5 RNAV and RNP Specific Functions. RNAV procedures are designed to define lateral, longitudinal and vertical navigation and waypoints are used to indicate a change in direction (track), speed and/or height. To indicate such a change one may use one of two types of waypoints, either a fly-by or a fly-over waypoint. The fly-by waypoint is used more often and is most commonly used in terminal RNAV procedures. a. Fly by waypoint: A waypoint demanding turn anticipation requiring the aircraft to start turning before it actually reaches the waypoint thus allowing tangential interception of the next segment of a route or procedure without the aircraft actually passing overhead (or through ) the waypoint. The amount of distance of turn anticipation (DTA) is dependent on aircraft speed and angle of back applied in the turn. All turns under Instrument Flight Rules (IFR) are executed as rate one turns (i.e. 3 per second) or 25 angle of bank, whichever is less bank. This means that at a higher speed the turn will be initiated sooner (further from the waypoint) than at a lower speed where the turn will be initiated later (closer to the waypoint). With a higher speed the turn radius will be larger than that for the same turn at a lower speed. This potential difference in flight path produced by aircraft at different speeds needs to be understood, particularly be approach controllers. ATNS/HO/C09/30/02/01 Page 40 of July 2010

41 b. Fly over waypoint: A waypoint at which the turn towards the next segment of a route or procedure is initiated. The turn is only initiated once that aircraft actually passes overhead (or through ) the waypoint. The extent to which the aircraft will overshoot the initial part of the next leg is again dependent on aircraft speed and angle of back applied in the turn. The resultant track error may be corrected in a number of ways and this will depend on the leg type of this leg. Remember all turns under IFR are executed as rate one turns or 25 angle of bank, whichever is less bank. 1.4 Required Navigation Performance (RNP) Specification Functional Capabilities and Limitations Functional Capabilities. a. RNP System Basic Functions. A RNP system is a RNAV system whose functionalities support on-board performance monitoring and alerting. Current specific requirements include: capability to follow a desired ground track with reliability, repeatability and predictability, including curved paths; and where vertical profiles are included for vertical guidance, use of vertical angles or specified altitude constraints to define a desired vertical path. The performance monitoring and alerting capabilities may be provided in different forms depending on the system installation, architecture and configurations, including: display and indication of both the required and the estimated navigation system performance; monitoring of the system performance and alerting the crew when RNP requirements are not met; and cross track deviation displays scaled to RNP, in conjunction with separate monitoring and alerting for navigation integrity. ATNS/HO/C09/30/02/01 Page 41 of July 2010

42 A RNP system utilises its navigation sensors, system architecture and modes of operation to satisfy the RNP navigation specification requirements. It must perform the integrity and reasonableness checks of the sensors and data, and may provide a means to deselect specific types of navigation aids to prevent reversion to an inadequate sensor. RNP requirements may limit the modes of operation of the aircraft, e.g. for low RNP, where flight technical error is a significant factor, manual flight by the crew may not be allowed. Dual system/sensor installations may also be required depending on the intended operation or need. b. RNAV and RNP Specific Functions. Performance-based flight operations are based on the ability to assure reliable, repeatable and predictable flight paths for improved capacity and efficiency in planned operations. The implementation of performance-based flight operations requires not only the functions traditionally provided by the RNAV system, but also may require specific functions to improve procedures, and airspace and air traffic operations. The system capabilities for established fixed radius paths, RNAV or RNP holding, and lateral offsets fall into this latter category. i. Lateral Navigation (LNAV): The primary sensors used for Area Navigation (laterally) are as follows: (1) Ground-based: VOR/VOR (Bearing/Bearing): requires 2 stations to estimate a position, however poor accuracy means that this is not used by RNAV systems. VOR/DME (Bearing/Range): The angular error from the VOR limits the maximum range for some navigation applications. DME/DME (Range/Range): requires a minimum of 2 DMEs (plus ambiguity resolution) to estimate a position, supports all navigation applications down to the Final Approach Fix (FAF). ATNS/HO/C09/30/02/01 Page 42 of July 2010

43 (2) Space -based: GPS and possibly GLONASS (once it becomes fully operational again): a 3D position solution is calculated by estimating the range from 4 satellites. ii. Vertical Navigation (VNAV): (although briefly mentioned here, VNAV will be discussed in more detail under All Weather Operations, Sensor Specific RNAV Procedures, Para a, page 114) There are 2 systems identified to support vertical navigation: Barometric Altimetry - BARO VNAV: Barometric Altimetry provides readings based on atmospheric pressure (temperature dependant). The approach path will become shallower in colder temperatures and steeper in higher temperatures. Geometric Altimetry: Geometric Altimetry is provided by GNSS. However, vertical accuracy of raw GPS is insufficient for aviation applications. Therefore, other systems have been developed to overcome this. c. RNAV System Limitations. There are also potential disadvantages to using RNAV in the terminal area: Controllers will need to provide services to both RNAV and non-rnav aircraft within the same airspace. RNAV databases and equipment are not fully standardised, and there is no firm guidance on how the information is processed by aircraft systems. Tracks may be flown slightly differently due to equipment, pilot technique or airline policies. However, these track differences should not be significant enough to appear as deviations from the published procedure. Initially, controllers may be uncertain of the expected aircraft behaviour during a RNAV turn, which may result in unnecessary vectors. A common factor in each case is that RNAV procedures in the terminal area are relatively new. Over time the number of RNAV operations will increase. Good procedure design, effective training, and experience with terminal RNAV will increase pilot and controller confidence in RNAV procedures RNAV System Requirements in terms of Accuracy, Integrity and continuity a. RNAV Accuracy. The precision with which a RNAV procedure is flown depends on the navigation source and on the aircraft onboard equipment and database. Even though a standard format exists (i.e., ARINC 424), the coding of a RNAV SID or STAR into a database (or the interpretation of that coding) may vary slightly. Differences in the databases along with variations in aircraft performance may result in slightly different tracks being flown by RNAV capable aircraft on the same procedure. This will be most apparent during turns and where fly-over waypoints ATNS/HO/C09/30/02/01 Page 43 of July 2010

44 are used. Tracking of a defined path by a RNAV capable aircraft is as accurate as, or better than, that of aircraft flying conventional routes. In fact RNAV is often used to fly conventional en route and terminal procedures PBN operations require (lateral) accuracy, integrity, continuity, and availability of aircraft systems together with particular RNAV computer functionalities to meet specific requirements. These requirements are defined for a particular Navigation Application in the associated Navigation Specification. The lateral track accuracy is defined by: the path that has been defined by the RNAV system, the navigation sensor used to estimate the position, and the ability of the pilot and system to fly the defined path. If the pilot or system is unable to maintain the defined path, this is known as the Flight Technical Error (FTE). The performance limits for the FTE are laid down by the ICAO for each RNP Specification. Position estimation accuracy is related to the type of navigation sensor used; each sensor has its own error value, called the Navigation Sensor Error (NSE). It is also linked to the dilution of precision' (DOP). DOP is dependent upon the relative angle the signals subtend at the aircraft (angle of cut) and can be considered the uncertainty in position estimation. Some sensors are better suited to RNAV (PBN) operations than others: NDB: is not an input to RNAV systems. VOR: at long range is the least accurate of the ground-based NAVAIDs used in Area Navigation, it is too inaccurate for the more demanding lateral track accuracy requirements. DME: providing there are sufficient stations with appropriate geometry, supports most Navigation Applications up to a simple approach the accuracy of a DME/DME position estimation is too poor when the DOP of the signals from a pair of stations subtend less than 30 and more than 150. ATNS/HO/C09/30/02/01 Page 44 of July 2010

45 GNSS (GPS and possibly other constellations): has the least error, with augmentation (integrity checking), provides a navigation solution for every Navigation Application. The aircraft manufacturers and AOs decide which sensors are fitted to the aircraft. b. Integrity. Integrity is the degree of confidence that can be placed on the position estimation by the RNAV system. For flight applications using RNP systems, failure to meet the integrity requirement should result in an alert to the pilot. This is also true for some RNAV systems. All RNAV Systems using GPS as primary navigation signal input are also designed to provide an alert in the event of navigation signal input failure and/or RAIM failure. GPS does not have an acceptable alerting system for civil aviation. To provide the required alert, Airborne Based Augmentation Systems (ABAS) is employed. ABAS provides integrity monitoring by: Aircraft Autonomous Integrity Monitoring (AAIM) links the GPS receiver to other aircraft systems, or Receiver Autonomous Integrity Monitoring (RAIM), which compares a series of position estimations within the GPS unit using redundant (extra) satellite signals TSO 129 receivers provide this functionality. All TSO 129 certified receivers are capable of Fault Detection (FD). AAIM: Integrity monitoring is provided on the flight deck by linking the GPS receiver with either an Inertial system or a Barometric altimeter. RAIM is the most common form of integrity monitoring. It is an algorithm integrated in the GPS receiver which compares a series of position estimations for internal consistency. All forms of GPS augmentation will be discussed under paragraph 2, GNSS. ATNS/HO/C09/30/02/01 Page 45 of July 2010

46 c. Availability and continuity. To meet a specific navigation application both the signals-in-space and the aircraft systems must meet the required accuracy, integrity and continuity for that operation. PBN requires that an aircraft and its systems should be able to perform for the whole of the defined operation, as long as it was operating correctly at the start of that operation. Equally, the signals from the NAVAIDs should also be available for the required operation and once the particular phase of flight has begun, continue to function for the period of that operation. The Service Provider will need to consider how to meet the appropriate requirement for signal availability and continuity. This is usually achieved through redundancy (additional capability to handle failures), or by the requirement for the aircraft to carry additional systems (for example, carriage of IRS/IRU). The probability of failure and therefore being unable to complete an operation must be acceptably low. d. On-board Performance Monitoring and Alerting. Aircraft RNAV systems do not necessarily provide the pilot with a warning when the required lateral accuracy limits have been exceeded. However, some RNAV systems do have extra functionality to monitor the navigation sensor error (NSE) and issue alerts. Those RNAV systems with this extra functionality (on-board monitoring and alerting) are RNP capable. Some navigation applications will require RNP capable systems for their operations. ATNS/HO/C09/30/02/01 Page 46 of July 2010

47 1.5 RNAV and RNP Specific Functions RNAV Leg types RNAV leg types are used to describe the path before, after or between waypoints. During the design phase of a RNAV SID or STAR the leg type for the each leg is defined by the procedure designers. The leg type may be any one of number of leg types ( path terminators ) as formulated by Aeronautical Radio Incorporated (AIRINC) in accordance with what is known as the AIRINC 424 Navigation Database Specification. The leg type is part of the information that is used to define each RNAV procedure and is contained in the data package that is used to build the navigation database. Generally only a few of the available leg types are used in the design of RNAV procedures. A two-letter code is used to describe the leg type (e.g., heading = V, course = C, track = T, etc.) and the leg end point (e.g., an altitude = A, distance = D, fix = F etc.). Although not explicitly depicted on charts, controllers and pilots can determine leg types (and thus the expected aircraft behaviour) by reading the relevant RNAV procedure chart narrative and viewing the graphic depiction. The most common leg types used are; A "track" is a magnetic course between waypoints that must be intercepted and flown. This is the most common leg type and is coded as "TF." Here the aircraft will "track" from ALPHA to BRAVO by intercepting the magnetic course between the two waypoints after correcting the track error resulting from the flying over ALPHA (ALPHA being a flyover waypoint). A "course" is a magnetic course to a waypoint that must be intercepted and flown. A "CF" leg differs from a "TF" only in that it does not have a beginning waypoint. "Direct" describes a direct course from an aircraft's position to a waypoint. A "DF" leg allows an immediate turn to a waypoint without requiring intercept of a particular course. Here the aircraft will ATNS/HO/C09/30/02/01 Page 47 of July 2010

48 proceed "direct" to BRAVO after crossing the fly-over waypoint ALPHA. A "heading" is a magnetic heading to be flown. Heading legs are subject to wind drift. A "VA" leg is a heading to an altitude and a "VM" is a heading to a "manual termination." The "VA" leg is often used as the first leg of a RNAV departure. The "VM" leg is most often used to end a RNAV STAR on, for example, a downwind leg heading. Below we see the combination of a VA, CF, and TF that has been used to create the initial portion of a RNAV SID. ATNS/HO/C09/30/02/01 Page 48 of July 2010

49 1.5.2 Fixed Radius Paths a. Radius to Fix (RF): This functionality is only used for Standard Instrument Departures (SIDs) and Standard Arrival Routes (STARs). b. Fixed Radius Transitions: These transitions are used for other Air Traffic Services (ATS) routes, usually at higher altitudes. The Fixed Radius Transitions (FRTs), used in the en-route phase of flight, have two turn radii: 15 NM below FL 190, 22.5 NM above FL 200. These values are defined in the industry standard DO236B/ED75B c. Leg: It is desirable to define how an aircraft will fly between waypoints, especially for consistent and predictable flight behaviour. The path between two waypoints is normally called a leg. With ATS routes, the aircraft will fly the leg to the next waypoint in sequence, performing a fly-by turn where capable. For consistent ground tracks in the turn, an FRT can be used. With SIDs and STARs each 'leg' is associated with a 'Path Terminator', which defines how the path will be flown and how the leg will be terminated. These Path Terminators have been defined by industry in a standard called ARINC 424. RF (Radius to Fix), used for SIDs and STARs, is an example of a 'leg' whose path is a fixed radius turn terminating at the next fix (which is a waypoint). Historically, the textual description of the SID or STAR in the States AIPs was the legal statement of that procedure. This has led to ambiguity for those creating aircraft databases. These issues are discussed in the topic 'Airspace Design'. ATNS/HO/C09/30/02/01 Page 49 of July 2010

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51 1.5.3 Holding Pattern The RNAV system facilitates the holding pattern specification by allowing the definition of the inbound course to the holding waypoint, turn direction and leg time or distance on the straight segments, as well as the ability to plan the exit from the hold. For RNP systems, further improvement in holding is available. These RNP improvements include fly-by entry into the hold, minimising the necessary protected airspace on the non-holding side of the holding pattern, consistent with the RNP limits provided. Where RNP holding is applied, a maximum of RNP 1 is suggested since less stringent values adversely affect airspace usage and design Offset Flight Path RNAV systems may provide the capability for the flight crew to specify a lateral offset from a defined route. Generally, lateral offsets can be specified in increments of 1 NM up to 20 NM. When a lateral offset is activated in the RNAV system, the RNAV aircraft will depart the defined route and typically intercept the offset at a 45⁰ or less angle. When the offset is cancelled, the aircraft returns to the defined route in a similar manner. Such offsets can be used both strategically, i.e. fixed offset for the length of the route, or tactically, i.e. temporarily. Most RNAV systems discontinue offsets in the terminal area or at the beginning of an approach procedure, at a RNAV hold, or during course changes of 90⁰s or greater. The amount of variability in these types of RNAV operations should be considered as operational implementation proceeds. ATNS/HO/C09/30/02/01 Page 51 of July 2010

52 2 GLOBAL NAVIGATION SATELLITE SYSTEMS (GNSS) 2.1 Description of the GNSS Concept Global Navigation Satellite Systems (GNSS) is the standard generic term for satellite navigation systems ( sat nav ) that provide autonomous geo-spatial positioning with global coverage. GNSS allows small electronic receivers to determine their location (longitude, latitude and altitude) to within a few metres using time signals transmitted along a line-of-sight by radio from satellites. Receivers calculate the precise time as well as position. As of 2010, the United States NAVSTAR Global Positioning System (GPS) is the only fully operational GNSS. The Russian GLONASS is a GNSS in the process of being restored to full operation (21 of 24 are operational). The European Union s Galileo positioning system is a GNSS in initial deployment phase, scheduled to be operational in 2013/2014. The People s Republic of China has indicated it will expand its regional Beidou navigation system into the global Compass navigation system by GNSS navigation services (i.e. position and time data) may be obtained using various combinations of the following elements installed on the ground, on satellites and/or on-board aircraft: Global Positioning System (GPS) that provides the standard positioning service (SPS); Global Navigation Satellite System (GLONASS) that provides the Channel of Standard Accuracy (CSA) navigation signal; Aircraft GNSS receivers GNSS Augmentation Systems; Aircraft-based augmentation system (ABAS) Satellite-based augmentation system (SBAS); Ground-based augmentation system (GBAS); Ground-based regional augmentation system (GRAS) Note that the position information provided by the GNSS to the user shall be expressed in terms of the World Geodetic System 1984 (WGS-84) geodetic reference datum. If GNSS elements, other than WGS-84 coordinates are employed, appropriate conversion parameters are to be employed. The time data provided by the GNSS to the user shall be expressed in a time scale that takes the Universal Time Coordinated (UTC) as reference. ATNS/HO/C09/30/02/01 Page 52 of July 2010

53 The basic GNSS concept is shown in the graphic below, which illustrates the steps involved in using GNSS to determine time and position then applying this information. Basic GNSS Steps Step 1 Satellites: GNSS satellites orbit the Earth. The satellites know their orbit ephemerides (the parameters that define their orbit) and the time very, very accurately. Ground-based control stations adjust the satellites ephemerides and time, when necessary. Step 2 Propagation: GNSS satellites regularly broadcast their ephemerides and time, as well as their status. GNSS radio signals pass through layers of the atmosphere to the user equipment. Step 3 Reception: GNSS user equipment receives the signals from multiple GNSS satellites then, for each satellite, recovers the information that was transmitted and determines the time of propagation, i.e. the time it takes the signals to travel from the satellite to the receiver. Step 4 Computation: GNSS user equipment uses the recovered information to compute time and position. Step 5 Application: GNSS user equipment utilises the position and time information in their applications, for example, navigation, surveying or mapping. GNSS satellite signals are quite complex. Describing these signals requires equally complex terminology such as pseudo-random, correlation and code division multiple access (CDMA). To explain these GNSS concepts, let us first discuss GPS satellite signals. GPS was designed as a positioning system for the US Department of Defence to provide highaccuracy position information for military applications. A lot of complexity was designed into the system to make it impervious to jamming and interference. Although military and civilian components ATNS/HO/C09/30/02/01 Page 53 of July 2010

54 of GPS are separate, some of the technologies used in the military component have been applied to the civilian component. The frequency plans (plans that describe the frequency, amplitude and width of signals) for each GNSS constellation are a little different. To illustrate GNSS concepts, however, the frequency and signal scheme used by GPS (as shown in the graphic below) will be briefly discussed. Conceptually, this is not much different than the frequency plan for cable or broadcast television channels. GPS Frequency Plan As shown in the graphic above, GPS satellites transmit information on the L1, L2 and L5 frequencies. You may ask, How can all GPS satellites transmit on the same frequencies? GPS works the way it does because of the transmission scheme it uses, which is called CDMA. CDMA is a form of spread spectrum. GPS satellite signals, although they are on the same frequency, are modulated by a unique pseudo-random digital sequence or code. Each satellite uses a different pseudo-random code. Pseudo-random means that the signal only appears random; in fact, it actually repeats after a period of time. Receivers know the pseudo-random code for each satellite. This allows receivers to correlate (synchronise) with the CDMA signal for a particular satellite. CDMA signals are at a very low level, but through this code correlation, the receiver is able to recover the signals and the information they contain. To illustrate, consider listening to a person in a noise-filled room. Many conversations are taking place, but each conversation is in a different language. You are able to understand the person because you know the language that they are speaking. If you are multi-lingual, you will be able to understand what other people are saying too. CDMA is similar to this. GPS operates in a frequency band referred to as the L-band; a portion of the radio spectrum between 1 and 2 GHz. L-band was chosen for several reasons, including: Simplification of antenna design. If the frequency had been much higher, user antennae may have had to be a bit more complex. Ionospheric delay is more significant at lower frequencies. Except through a vacuum, the speed of light is lower at lower frequencies, as is evident by the separation of the colours in light by a prism. The coding scheme requires a high band-width, which was not available in every frequency band. The frequency band was chosen to minimise the effect that weather has on GPS signal propagation. ATNS/HO/C09/30/02/01 Page 54 of July 2010

55 GPS Navigation Message The P(Y) code is for military use. It provides better interference rejection than the C/A code, which makes military GPS more robust than civilian GPS. The L2 frequency transmits the P(Y) code and on newer GPS satellites, it also transmits the C/A code (referred to as L2C), providing a second publicly available code for civilian users. While the GPS transmission scheme is complex, it was chosen for many good reasons: GPS receivers can recover very weak signals using very small antennae. This keeps the receiver cost low. Multi-frequency operation allows for ionospheric compensation, since ionospheric delays vary with frequency. The GPS is resistant to jamming and interference. Security. Signals accessed and used by military applications are not accessible by civilians. Other global navigation satellites systems are conceptually similar to GPS, but there are slight differences (will be discussed at a later stage). Why does time play such an important role in GNSS? It is because the time it takes a GNSS signal to travel from satellites to receivers is used to determine distances (ranges) to satellites. Accuracy is required because radio waves travel at the speed of light. In one microsecond (a millionth of a second), light travels 300 m. In a nanosecond (a billionth of a second), light travels 30 cm. Small errors in time can therefore result in large errors in position. How does GNSS positioning actually work? For each satellite being tracked, the receiver calculates how long the satellite signal took to reach it, as follows: Propagation time = Time signal reached receiver Time signal left satellite ATNS/HO/C09/30/02/01 Page 55 of July 2010

56 Multiplying this propagation time by the speed of light gives the distance to the satellite. For each satellite being tracked, the receiver now knows where the satellite was at the time of transmission (because the satellite broadcasts its orbital ephemerides) and it has determined the distance to the satellite when it was there. Using trilateration, a method of geometrically determining the position of an object, in a manner similar to triangulation, the receiver calculates its position. To help you understand trilateration, the technique is described in two dimensions. The receiver calculates its range to Satellite A. As mentioned, it does this by determining the amount of time it took for the signal from Satellite A to arrive at the receiver, and multiplying this by the speed of light. Satellite A communicated its location (determined from the satellite orbit ephemerides and time) to the receiver, so the receiver knows it is somewhere on a circle radius equal to the range and centred at the location of Satellite A, as illustrated in the graphic on the right. In three dimensions, you would show ranges as spheres, not circles, but the explanation will continue by referring to circles. Ranging to First Satellite The receiver also determines its range to a second satellite, Satellite B. Now the receiver knows it is at the intersection of two circles, at either Position 1 or 2 as shown in the graphic below. Ranging to Second Satellite ATNS/HO/C09/30/02/01 Page 56 of July 2010

57 You may be tempted to conclude that ranging to a third satellite would be required to resolve your location to Position 1 or Position 2. But one of the positions can most often be eliminated as not feasible because, for example, it is in space or in the middle of the Earth. You might be tempted to extended this illustration to three dimensions and suggest that only three ranges are needed for positioning. But as have been discussed earlier, four ranges are necessary. Why is this? Receiver clocks are not nearly as accurate as the clocks on board the satellites. Most are based on quartz crystals and are accurate to only about 5 parts per million. If you multiply this by the speed of light, it will result in an accuracy of ± metres. When you determine the range to two satellites, your computed positions will be out by an amount proportional to the inaccuracy in your receiver clock, as illustrated in the graphic on the right. Position Error You want to determine your actual position but, as shown in the previous graphic, the receiver time inaccuracy causes range errors that result in position errors. The receiver knows there is an error; it just does not know the size of the error. If you now compute the range to a third satellite, it will not intersect the computed position as illustrated in the graphic below. Detecting Position Error Now let us discuss one of the ingenious techniques used in GNSS positioning. The receiver knows that the reason the pseudo-ranges to the three satellites are not intersecting is because its clock is ATNS/HO/C09/30/02/01 Page 57 of July 2010

58 inaccurate. The receiver is programmed to advance or delay its clock until the pseudo-ranges to the three satellites converge at a single point as illustrated in the graphic below. Convergence The incredible accuracy of the satellite clock has now been transferred to the receiver clock, eliminating the receiver clock error in the position determination. The receiver now has both accurate position and a very, very accurate time. This presents opportunities for a broad range of application, such as navigation in commercial aviation. The technique discussed shows how, in a two-dimensional representation, receiver time inaccuracy can be eliminated and position determined using ranges from three satellites. When you extend this technique to three dimensions, you need to add a range to a fourth satellite. This is the reason why line-of-sight to a minimum of four GNSS satellites is needed to determine position. There are various errors that can affect the accuracy of standard GNSS pseudo-range determination, i.e. the determination of the pseudo-range to a single satellite. These errors are shown in the table below: Table: GNSS Errors Contributing Source Satellite clocks Orbit errors Ionospheric delays Tropospheric delays Receiver noise Multipath Error Range ± 2 m ± 2.5 m ± 5 m ± 0.5 m ± 0.3 m ± 1 m The degree with which the above pseudo-range errors affect positioning accuracy depends largely on the geometry of the satellites being used. Techniques for reducing these errors will be discussed at a later stage. ATNS/HO/C09/30/02/01 Page 58 of July 2010

59 Once the receiver has determined its position and time, this information is passed to and used by the user application, such as a flight management system. Various GNSS Receivers Almanac The almanac consists of coarse orbit and status information for each satellite in the GNSS constellation, an ionospheric model, and information to relate satellite-derived time to Coordinated Universal Time (UTC). In order to fully comprehend the role of the almanac it is necessary to first describe the radio signals (navigation message) sent by a satellite. GNSS Navigation Message ATNS/HO/C09/30/02/01 Page 59 of July 2010

60 L1 transmits a navigation message, the coarse acquisition (C/A) code (freely available to the public) and an encrypted precision (P) code, called the P(Y) code (restricted access). The navigation message is a low bit rate message that includes the following information: GPS date and time; Satellite status and health. If the satellite is having problems or its orbit is being adjusted, it will not be usable. When this happens, the satellite will transmit the out-of-service message. Satellite ephemeris data, which allows the receiver to calculate the satellite s position. This information is accurate to many, many decimal places. Receivers can determine exactly where the satellite was when it transmitted its time. Almanac, which contains information and status for all GPS satellites, so receivers know which satellites are available for tracking. On start-up, a receiver will recover this almanac. The almanac consists of coarse (rough) orbit and status information for each satellite in the constellation. Each satellite continuously broadcasts a data signal containing navigational information. The information consists of a 50 Hs signal and contains data that include satellite orbits, clock corrections and other system parameters (i.e. information about the status of the satellite). The complete data signal consists of bit and a transmission rate of 50 bit/second means that 12.5 minutes are necessary to receive the complete signal. This time is required by the receiver until the first determination of a position is possible, if no information about the satellites is stored or the information is outdated. The data signal is divided into 25 frames, each having a length of bit (meaning an interval of 30 seconds for transmission). Structure of the GPS Data of One Frame The 25 frames are divided into sub-frames (300 bit/6 sec), which are again divided into 10 words each (30 bit/0.6 sec). The first word of each sub-frame is the TLM (telemetry word); it contains information about the age of the ephemeris data. The next word is the HOW (hand over word), which is used by military receivers. The rest of the first sub-frame contains data about status and accuracy of the transmitting satellite as well as clock correction data. The second and third sub-frames contain ephemeris parameters. Sub-frames four and five contain the so-called almanac data which include information about orbit parameters of all satellites, their technical status and actual configuration, identification number, etc. Every 30 seconds the most important data for the position determination are transmitted. From the almanac data the receiver identifies the satellites that are likely to be received at the actual position of the receiver. The receiver limits its search to those previously defined satellites and hence this accelerates the position determination. ATNS/HO/C09/30/02/01 Page 60 of July 2010

61 As mentioned earlier, the data signal contains a correction parameter for the satellite s clocks. Why is this necessary if the atomic clocks are absolutely precise? Each satellite carries several atomic clocks and has very accurate time. However, the atomic clocks of the individual satellites are not synchronised to the GPS reference time, but run independently of each other (periodic adjustments are made to align the timing of these clocks). Therefore, correction data for the clocks of each satellite are required. Furthermore, the GPS reference time is different from the UTC time. UTC is synchronised with the rotation of the Earth by means of leap seconds. A typical reason why satellites are marked as defective is the necessity for an orbit correction. In such a case the satellite is marked as defective, once the satellite is stabilised in its new orbit, the defective marking is removed. When ephemeris and almanac data are stored in the receiver, the age of the data will influence how long the receiver needs to calculate the first position determination. If the receiver has not had any contact with the satellites for an extended period of time, the first position determination will take longer. If the contact has only been interrupted for a short time (e.g. the aircraft was on the hardstand for a quick turn-around), the position determination is restarted instantly. Establishing GNSS position calculation using visible satellites with good geometry is known as reacquisition (or reacquire). If position and time are known and the almanac and ephemeris data are up-to-date, the system is able to reacquire the satellites almost instantaneously; this is referred to as a hot start. This is the case when the receiver is turned on at approximately the same position where it was turned off and within 2 6 hours after the last position determination. In this case a position fix can be obtained within approximately 15 seconds (this may happen during a quick turn-around or a short stop). If the almanac data are available and the time of the receiver is correct but the ephemeris data are outdated, the reacquisition will take a bit longer and this is referred to as a warm start. In this case it takes about 45 seconds to actualise the ephemeris data and obtain a position fix. Ephemeris data are outdated when more than 2 6 hours have elapsed since the last data reception from the satellites in view. The more new satellites have come into view since the last position determination, the longer the warm start takes. If neither ephemeris nor almanac data and the last position are known, the acquisition process is started with no known information; this is referred to as a cold start. The first step then is that all the almanac data have to be collected from the satellites; this procedure takes up to 12.5 minutes. This happens when the receiver was switched off for several hours, was stored without batteries or was moved approximately 300 km or more since the last position fix. In the last case no almanac data have to be collected, but as the wrong satellites are in view, the receiver has to screen all the satellite data until it finds the information for the satellites that are in view. For many receivers, the duration of a cold start can be shortened when the date and approximate position are entered manually GNSS Segments The GNSS consists of three major components or segments : the space segment, the control segment and the user segment. These are illustrated in the graphic below. ATNS/HO/C09/30/02/01 Page 61 of July 2010

62 GNSS Segments a. Space Segment The space segment is composed of the GNSS satellites orbiting about km above the Earth. Each GNSS has its own constellation of satellites, arranged in orbits to provide the desired coverage as illustrated in the graphic on the right. GNSS Satellite Orbits Each satellite in a GNSS constellation broadcasts a signal that identifies it and provides its time, orbit and status. To illustrate, consider the following: You are in town and decide to phone a friend for a visit. You call and reach your friend s answering service, so you leave a message: This is Peter (identity). The time is 2:30 PM (time). I am at the northwest corner of 1 st Avenue and 2 nd Street and I am heading towards your place (orbit). I am okay, but I am a bit thirsty (status). ATNS/HO/C09/30/02/01 Page 62 of July 2010

63 Your friend returns a couple of minutes later, listens to your message and processes it, then calls you back and suggest that you proceed via a slightly different route; effectively, your friend has given you an orbit correction. b. Control Segment The control segment comprises a ground-based network of master control stations, data uploading stations, and monitor stations; in the case of GPS for example, two master control stations (one primary and one back-up), four data uploading stations and ten monitor stations, located throughout the world. In each GNSS, the master control station adjusts the satellites orbit parameters and on-board high-precision clocks when necessary to maintain accuracy. Monitor stations, usually installed over a broad geographic area, monitor the satellites signals and status, and relay this information to the master control station. The master control station analyses the signals then transmits orbit and time corrections to the satellites through data uploading stations. GPS ground control station in Hawaii c. User Segment The user segment consists of equipment that processes the received signals from the GNSS satellites and uses them to derive an apply location and time information. The equipment ranges from hand-held receivers used by hikers, to sophisticated, specialised receivers used for high-end survey and mapping applications and commercial aviation. A Variety of Hand-held GPS Receivers In general, GNSS receivers are composed of an antenna, tuned to the frequencies transmitted by the satellites, receiver processors and a highly-stable clock (often a crystal oscillator). GNSS receivers therefore convert the GNSS satellite signals into position, and time estimates. Four satellites are required to compute the four dimensions of X, Y, S (GNSS WGS 84 position is expressed in terms of three axis X, Y and S) and time. Some receivers may also include a display for providing location and speed information to the user (speed can only be calculated if the GNSS receiver has a built-in area navigation computer to calculate speed). A receiver is often described by the number of channels it is capable of monitoring simultaneously. Originally limited to four or five satellites, this has progressively increased over the years so that today receivers typically have between 12 and 20 channels. ATNS/HO/C09/30/02/01 Page 63 of July 2010

64 2.2 System Accuracy, Integrity, Continuity and Availability The current core constellations (i.e. GPS and GLONASS) have the capability to provide accurate position and time information worldwide. The accuracy provided by these systems meets aviation requirements for en-route through non-precision approach, but not the requirements for precision approach. Augmentation systems are used to meet the four basic GNSS navigation operational performance requirements: accuracy, integrity, continuity and availability. Navigation systems should be evaluated against these four essential criteria before being introduced. Availability is the cornerstone of these specifications in that it denotes the availability of accuracy with integrity and continuity. The level of service and operational restrictions that could be imposed depends on the level of availability of that service Signal Performance Requirement GNSS position accuracy is the difference between the calculated and actual position of the aircraft. Ground-based systems such as VOR and ILS have relatively repeatable error characteristics, and therefore their performance can be measured for a short period of time (e.g. during flight calibration) and it is assumed that the system accuracy does not change after the measurement. GNSS errors however can change over a period of hours due to satellite geometry changes, the effects of the ionosphere and augmentation system design. While errors can change quickly for core satellite constellations, satellite-based augmentation system and ground-based augmentation system errors would change slowly over time. Integrity is a measure of the trust which can be placed in the correctness of the information supplied by the total system. Integrity includes the ability of the system to alert the user when the system should not be used for the intended operation (or phase of flight). The necessary level of integrity for each operation is established with respect to specific horizontal/lateral (and for some approaches, vertical) alert limits. When the integrity estimates exceed these limits, the pilot is alerted within the prescribed time period. The type of operation and the phase of flight dictate the maximum allowable horizontal/lateral and vertical errors and the maximum time to alert the pilot. These are shown in the table below: Table: GNSS Integrity Alert Limits by Airspace Operation: Oceanic en-route Terminal Continental enroute Nonprecision approach Approach procedure with vertical guidance (APV) APV-I APV-II Category I Horizontal & Lateral alert limit 7.4 km (4 NM) 7.4 to 3.7 km (4 to 2 NM) 1.85 km (1 NM) 556 m (0.3 NM) 40 m (130 ft) 40 m (130 ft) 40 m (130 ft) Vertical alert limit Maximum alert time N/A N/A N/A N/A 50 m (164 ft) 20 m (66 ft) 10 to 15 m (33 to 50 ft) 5 min 5 min 15 sec 10 sec 6 sec 6 sec 6 sec Following an alert, the crew should either resume navigation using traditional navigation aids (NAVAIDs) or comply with procedures linked to a GNSS-based level of service with less stringent requirements. For example, if alert limits are exceeded for Category I precision ATNS/HO/C09/30/02/01 Page 64 of July 2010

65 approach, before the aircraft crosses the final approach fix, the crew could restrict descend to a decision altitude associated with APV operation. Continuity is the capability of the system to perform its function without unscheduled interruptions during the intended operation. This is expressed as a probability. For example, there should be a high probability that the service remains available throughout a full instrument approach procedure. Continuity requirements vary from a lower value for low traffic density en-route airspace to a higher value for areas with high traffic density and airspace complexity, where a failure could affect a large number of aircraft. Where there is a high degree of reliance on the system for navigation, mitigation against failure may be achieved through the use of alternative (most often conventional) navigation means or through the use of air traffic control surveillance (most often radar monitoring) and intervention to ensure that separation is maintained. For approach and landing operations, each aircraft can be considered individually. The results of a disruption of service would normally relate only to the risks associated with a missed approach. For non-precision, APV and Category I approaches, missed approach is considered a normal operation, since it occurs whenever the aircraft descends to the minimum altitude for the approach and the pilot is unable to continue with visual reference. This is therefore an operational efficiency issue, not a safety issue. The availability of a service is the portion of time during which the system is simultaneously delivering the required accuracy, integrity and continuity. The availability of GNSS is complicated by the movement of satellites relative to a coverage area and by the potentially long time it takes to restore a satellite in the event of a failure. The level of availability for a certain airspace at a certain time should be determined through design, analysis and modelling, rather than through measurement. The availability specifications (i.e. signal-inspace performance requirements) in the table below, present a range of values valid for all phases of flight. When establishing the availability requirements for GNSS, the desired level of service to be supported is considered. Availability should be directly proportional to the reliance on a GNSS element used in support of a particular phase of flight. Typical Operation En-route En-route, Terminal Initial approach, Intermediate approach, Non-precision approach (NPA), Departure Approach operations with vertical guidance (APV-I) Approach operations with vertical guidance (APV-II) Table: Signal-in-space Performance Requirements Accuracy Horizontal 95% (Notes 1 and 3) 3.7 km (2.0 NM) 0.74 km (0.4 NM) 220 m (720 ft) 16.0 m (52 ft) 16.0 m (52 ft) Accuracy Vertical 95% (Notes 1 and 3) Integrity (Note 2) Time-toalert (Note 3) Continuity (Note 4) N/A 1 1 x 10-7 /h 5 min 1 1 x 10-4 /h to 1 1 x 10-8 /h N/A 1 1 x 10-7 /h 15 sec 1 1 x 10-4 /h to 1 1 x 10-8 /h N/A 1 1 x 10-7 /h 10 sec 1 1 x 10-4 /h to 1 1 x 10-8 /h 20 m (66 ft) 8 m (26 ft) 1 2 x 10-7 /h in any approach 1 2 x 10-7 /h in any approach 10 sec 1 8 x 10-6 /h per 15 sec 6 sec 1 8 x 10-6 /h per 15 sec Availability (Note 5) 0.99 to to to to to ATNS/HO/C09/30/02/01 Page 65 of July 2010

66 Category I precision approach (Note 7) Notes: 16.0 m (52 ft) 6.0 m to 4.0 m (20 ft to 13 ft) (Note 6) 1 2 x 10-7 /h in any approach 6 sec 1 8 x 10-6 /h per 15 sec 0.99 to The 95 th percentile values for GNSS position errors are those required for the intended operation at the lowest height above threshold (HAT), if applicable. Detailed requirements are specified in Annex 10 Volume 1 Appendix B and guidance material is given in Attachment D, The definition of the integrity requirement includes an alert limit against which the requirement can be assessed. These alert limits are: A range of vertical limits for Category I precision approach relates to the range of vertical accuracy requirements. Typical Operation Horizontal alert limit Vertical alert limit En-route (oceanic/continental low density 7.4 km (4 NM) N/A En-route (continental) 3.7 km (2 NM) N/A En-route, Terminal 1.85 km (1 NM) N/A NPA 556 m (0.3 NM) N/A APV-I 40 m (130 ft) 50 m (164 ft) APV-II 40 m (130 ft) 20 m (66ft) Category I precision approach 40 m (130 ft) 15 m to 10 m (50 ft to 33 ft) 3. The accuracy and time-to-alert requirements include the nominal performance of a fault-free receiver. 4. Ranges of values are given for the continuity requirement for en-route, terminal, initial approach, NPA and departure operations, as this requirement is dependent upon several factors including the intended operation, traffic density, complexity of airspace and availability of alternative navigation aids. The lower value given is the minimum requirement for areas with low traffic density and airspace complexity. The higher value given is appropriate for areas with high traffic density and airspace complexity. Continuity requirements for APV and Category I operations apply to the average risk (over time) of loss of service, normalised to a 15-second exposure time. 5. A range of values is given for the availability requirements as these requirements are dependent upon the operational need which is based upon several factors including the frequency of operations, weather environments, the size and duration of the outages, availability of alternate navigation aids, radar coverage, traffic density and reversionary operational procedures. The lower values given are the minimum availabilities for which a system is considered to be practical but are not adequate to replace non-gnss navigation aids. For en-route navigation, the higher values given are adequate for GNSS to be the only navigation aid provided in an area. For approach and departure, the higher values given are based upon the availability requirements at airport with a large amount of traffic assuming that operations to or from multiple runways are affected but reversionary operational procedures ensure the safety of the operation. 6. A range of values is specified for Category I precision approach. The 4.0 m (13 ft) requirement is based upon ILS specifications and represents a conservative derivation from these specifications. 7. GNSS performance requirements for Category II and III precision approach operations are under review and will be included at a later date. 8. The terms APV-I and APV-II refer to two levels of GNSS approach and landing operations with vertical guidance (APV) and these terms are not necessarily intended to be used operationally. Traffic density, alternate NAVAIDs, primary/secondary surveillance coverage, potential duration and geographic size of outages, flight and ATC procedures are considered when setting availability specifications for airspace, especially if the decommissioning of traditional NAVAIDs is being considered. An availability prediction tool can determine the periods when GNSS will not support an intended operation. If this tool is used in flight planning, then from an operational perspective, there remains only a continuity risk associated with the failure of necessary system components between the time the prediction is made and the time the operation is conducted. ATNS/HO/C09/30/02/01 Page 66 of July 2010

67 2.3 Augmentation The existing core satellite constellations alone do not meet strict aviation requirements of accuracy, integrity, continuity and availability. They meet the operational requirements for various phases of flight, the core satellite constellations require augmentation in the form of aircraft-based augmentation systems (ABAS), satellite-based augmentation systems (SBAS) and/or ground-based augmentation systems (GBAS). ABAS for example, rely on avionics processing techniques or avionics integration to meet aviation requirements. The other two augmentation use ground monitoring stations to verify the validity of satellite signals and calculate corrections to enhance accuracy. EGNOS Augmentation Satellite SBAS delivers this information via a geostationary Earth orbit satellite, while GBAS uses a VHF data broadcast (VDB) from a ground station. The table below shows the potential of ABAS, SBAS or GBAS to meet the navigation requirements for a particular phase of flight. However, the use of a specific augmentation system or a combination of augmentation systems for specific operations within specified airspace needs to be approved by the Appropriate Authority. Under risk management principles, some operational limitations may be applied to compensate for availability or continuity performance that is lower than the specified levels. Table: Level of Service from GNSS Augmentation Elements Augmentation element/operation Oceanic en-route Continental en-route Terminal Instrument approach and landing* Core satellite constellation with ABAS Suitable for navigation when fault detection and exclusion (FDE) is available. Pre-flight FDE predictions might be required Suitable for navigation when receiver autonomous integrity monitoring (RAIM) or another navigation source is usable. Suitable for navigation when RAIM or another navigation source is usable. Suitable for nonprecision approach (NPA) when RAIM is available and another navigation source is usable at the alternate aerodrome. Core satellite constellation with SBAS Suitable for navigation. Suitable for navigation. Suitable for navigation. Suitable for NPA and APV, depending on SBAS performance. Core satellite constellation with GBAS N/A GBAS positioning service output may be used as an input source for approved navigation systems. GBAS positioning service output may be used as an input source for approved navigation systems. Suitable for NPA and precision approach (PA) Category I (potentially Category II and Category III. * Specific aerodrome infrastructure elements and physical characteristics are required to support the visual segment of the instrument approach. These are defined in Annex 14 Aerodromes and Aerodrome Design Manual (Doc 9157). Various techniques have been developed (and are used by the augmentation systems) for extending and improving the achievable accuracy. These techniques include dilution of precision; differential ATNS/HO/C09/30/02/01 Page 67 of July 2010

68 GNSS; carrier-based techniques and inertial navigation systems (these will be discussed at a later stage) Ground-Based Augmentation System (GBAS) GBAS is a system for the augmentation of the accuracy, integrity, continuity and availability of the information for navigation using GNSS. The GBAS ground sub-systems are Range Reference stations (RRS); VHF data broadcast stations (VDB), Integrity monitoring stations (IMS) and Processing base stations (PBS), integrated to execute the following main functions: Provide locally relevant pseudo-range corrections; Provide GBAS-related data; Provide Final Approach Segment (FAS) data when supporting precision approach; Provide predicted ranging source availability data; and Provide monitoring of integrity for GNSS ranging sources. The RRS receives the signals from the satellites that are in-view and provides pseudo-ranges for the PBS. The PBS processes data and calculates the pseudo-range errors, including the ranging sources availability, GBAS-related, final approach segment and atmospheric effects data, and prepares the digital messages to be sent to the aircraft through the VDB. The IMS monitors the operational state and the integrity of the GBAS ground sub-system elements, as well as, the messages content, signals emitted by the VDB and quality of the obtained pseudo-range errors. Another IMS function is to avoid that messages containing misleading information be sent to the aircraft. The VDB broadcasts the GBAS messages to aircraft operating inside its coverage. GBAS is intended to support all types of approach, landing, take-off and surface operations and may support en-route and terminal operations. The supported services are: Category I precision approach; Approach with vertical guidance; and GBAS positioning information. Probably the most well-known GBAS is the US developed Local Area Augmentation System (LAAS), which is an all-weather aircraft landing system based on real-time differential correction of the GPS signal. Local reference receivers, located around the airport, send data to a central location at the airport. This data is used to formulate a correction message, which is then transmitted to users via a VHF data link. A receiver on-board the aircraft uses this information to correct GPS signals, which then provide a standard ILS-style display to use while flying a precision approach. ATNS/HO/C09/30/02/01 Page 68 of July 2010

69 LAAS Architecture Aircraft-Based Augmentation System (ABAS) The core satellite constellations were not developed to satisfy the strict requirements for IFR navigation. For this reason, GNSS avionics used in IFR operations should augment the GNSS signal to ensure, amongst other things, its integrity. ABAS augments and/or integrates GNSS information with information available on-board the aircraft to enhance the performance of the core satellite constellations. ABAS requires the use of one of the following techniques to enhance the performance (accuracy, integrity, continuity and/or availability) of unaugmented GNSS and/or of the aircraft navigation system: Receiver Autonomous Integrity Monitoring (RAIM), which compares a series of position estimations within the GPS unit using redundant (extra) satellite signals; or Aircraft Autonomous Integrity Monitoring (AAIM), which links the GPS receiver to other aircraft systems. Integrity monitoring is provided on the flight deck by linking the GPS receiver with either an Inertial system or a Barometric altimeter. a. Aircraft Autonomous Integrity Monitoring (AAIM). AAIM uses the redundancy of position estimates from multiple sensors, including INS, conventional NAVAIDs and/or GNSS, to provide integrity performance monitoring that is at least equivalent to RAIM. This may be achieved by the use of INS or conventional navigation sensors as an integrity check on GNSS data when RAIM is unavailable but GPS positioning information continues to be valid. ATNS/HO/C09/30/02/01 Page 69 of July 2010

70 Non-GNSS information can be combined with GNSS information to enhance the performance of the RNAV system. Examples include: Using INS or Conventional NAVAIDs as the position inputs to coast through short periods of poor satellite geometry or when the aircraft structure shadows the GNSS antennae while manoeuvring; and Using GNSS sensor data as an input to a multi-sensor navigation solution calculated by a RNAV system. This augmentation improves the availability of the aircraft s navigation function. b. Receiver Autonomous Integrity Monitoring (RAIM) The most common ABAS technique is called RAIM. As mentioned above, RAIM requires redundant satellite range measurements to detect faulty signals and alert the pilot. The requirement for redundant signals means that navigation guidance with integrity, provided by RAIM, may not be available 100% of the time. RAIM requirements may vary depending on the type of operation; the requirements are lower for a non-precision approach than for terminal applications, and are lower for terminal use than for en-route. It is for this reason that GPS/RAIM approvals usually have operational restrictions. RAIM algorithms require a minimum of five satellites in order to perform fault detection and detect the presence of an unacceptably large position error for a given mode of flight. FDE uses a minimum of six satellites not only to detect a faulty satellite but also to exclude it from the navigation solution so that the navigation function can continue without interruption. There are two distinct events that can cause a RAIM alert. The first is when there are not enough satellites with adequate geometry in view. The position estimate may still be accurate, but the integrity function of the receiver, i.e. the ability to detect a failed satellite, is lost. The second is when the receiver detects a satellite fault and excludes this satellite from the position calculation process (FDE). This type of alert results in the loss of the capability to navigate based on GNSS position information. If either alert is experienced whilst on approach, the pilot may no longer rely on GNSS position information for the purpose of navigation during the remainder of the approach. A barometric altimeter may be used as an additional measurement so that the number of ranging sources required for RAIM and FDE can be reduced by one. Baro-aiding can also help to increase availability when there are enough visible satellites, but their geometry is not adequate to perform integrity function Space-Based Augmentation System (SBAS) For applications where the cost of a differential GNSS augmentation system is not justified, or if rover stations are spread over too large an area, spaced-based (or satellite-based) augmentation systems (SBAS) may be more appropriate for enhancing position accuracy. SBAS uses geosynchronous satellite systems that provide services for improving the accuracy, integrity, and availability of GNSS signals. ATNS/HO/C09/30/02/01 Page 70 of July 2010

71 Accuracy is enhanced through the transmission of wide-area corrections for GNSS range errors. Integrity is enhanced by the SBAS network quickly detecting satellite signal errors and sending alerts to receivers that they should not track the failed satellite. Signal availability can be improved if the SBAS transmits ranging signals from its satellites. SBAS include reference stations, master stations, up-link stations and geosynchronous satellites as illustrated in the graphic below. Reference stations, which are geographically distributed throughout the SBAS service area, receive GNSS signals and forward them to the master station. Since the locations of the reference stations are accurately known, the master station can accurately calculate wide-area corrections. SBAS GNSS Data Gathering As shown in the graphics below, corrections are up-linked to the SBAS satellite (left), then broadcast to GNSS receivers throughout the SBAS coverage area (right). SBAS Correction Calculation and Up-link SBAS Correction Broadcast ATNS/HO/C09/30/02/01 Page 71 of July 2010

72 User equipment receives the corrections and applies them to range calculations. SBAS services can be grouped into two categories: free SBAS services and commercial SBAS services. In general, free government-provided SBAS services use the same frequency as GPS (CDGPS is an exception), and commercial SBAS services (such as OmniSTAR and StarFire systems) use a different frequency. In this case additional equipment may be required. The following section provides a brief overview of some of the free SBAS services that have been implemented around the world or are planned: Wide Area Augmentation System (WAAS) has been developed by the US Federal Aviation Administration (FAA) to provide GPS corrections and a certified level of integrity to the aviation industry, to enable aircraft to conduct varying levels of precision approach to airports. The corrections are also available free of charge to civilian users in North America. The Wide Area Master Station (WMS) receives GPS data from Wide Area Reference Stations (WRS) located throughout the USA. The WMS calculates differential corrections, then up-link these to two WAAS geostationary satellites for broadcast across the USA as shown in the WAAS architecture graphic below. Separate corrections are calculated for ionospheric delay, satellite timing and satellite orbits; this allows error corrections to be processed separately, if appropriate, by the user application. WAAS broadcasts correction data on the same frequency as GPS, which allows for the use of the same receiver and antenna equipment as that used for GPS. To receive correction data, user equipment must have line-of-sight to one of the WAAS satellites. GPS Receiver display with WAAS Wide Area Augmentation System (WAAS) Architecture ATNS/HO/C09/30/02/01 Page 72 of July 2010

73 The European Space Agency, in co-operation with the European Commission (EC) and Euro- Control (European Organisation for the Safety of Air Navigation) has developed the European Geostationary Navigation Overlay System (EGNOS), a regional augmentation system that improves the accuracy of positions derived from GPS signals and alerts users about reliability of the GPS signals. The EGNOS satellites cover the European Union member nations and several other countries in Europe. EGNOS is expected to be certified for safety-of-life applications in It transmits differential correction data for public use. EGNOS satellites have also been placed over the eastern Atlantic Ocean, the Indian Ocean, and the African mid-continent. EGNOS Architecture In Japan, the MTSAT satellite-based augmentation system (MSAS) has been developed by the Japan Civil Aviation Bureau (JCAB). Successful launches of MTSAT-1R and MTSAT-2 were followed by integration of the MSAS ground system with the MTSATs by transmitting test signals from MTSATs. The purpose of these test signal transmissions were to optimise system performance and then to verify that augmentation information meets safety and performance requirements. Since those tests had been accomplished successfully, MSAS for aviation use was commissioned in September MSAS Architecture ATNS/HO/C09/30/02/01 Page 73 of July 2010

74 In India, the Indian Space Research Organisation (ISRO) and Airports Authority of India have successfully completed the final system acceptance test of the GPS Aided GEO Augmented Navigation System (GAGAN). With completion of the final system acceptance test, the stage is set for India to embark on the next phase of the programme, which will expand the existing ground network, add redundancy, and produce the certified analysis and documentation for safety-of-flight commissioning. Proposed GAGAN constellation China is also planning SNAS (Satellite Navigation Augmentation System), to provide WAAS-like service for the China-region. The graphic below depicts the current world SBAS coverage. This graphic is only an approximation of signal coverage by each of the SBAS constellations. Although there is geographic coverage at higher latitudes, practical usage of SBAS will be limited to environments where a relatively consistent line-of-sight to the satellites is available. SBAS Global Footprint ATNS/HO/C09/30/02/01 Page 74 of July 2010

75 2.3.4 Ground-Based Regional Augmentation (GRAS) GRAS is a blending of SBAS/GBAS concepts intended to enhance GPS/GNSS capabilities for supporting civilian navigation needs. This approach is SBAS-like in its use of a distributed network of reference stations for monitoring GPS and a central processing facility for computing GPS integrity and differential correction information. But instead of transmitting this information to users via dedicated Geostationary Earth Orbit (GEO) satellites, GRAS delivers SBAS message data to a network of terrestrial stations for a local check as well as for reformatting and rebroadcasting in the GBAS format in the MHz band. Each terrestrial station emits a GBAS-like VHF data broadcast (VDB) signal in a managed time slot. Users can employ a GPS/GRAS-capable receiver to obtain GPS augmentation data for both continental en-route as well as terminal approach/departure operations, depending on the VHF network coverage. The GRAS approach could be beneficial where a GEO satellite is either not available or too costly to broadcast SBAS data. GRAS also allows for national control of the system while providing unified corrections and integrity for en-route capability. VHF Data Broadcast Antenna Techniques to improve GNSS receiver performance As mentioned previously, various techniques have been developed to extend the accuracy of GNSS receivers. A commonly used technique for improving GNSS performance is differential GNSS, which is illustrated in the graphic below. Differential GNSS Using differential GNSS, the position of a fixed GNSS receiver, referred to as the base station is determined to a high degree of accuracy using conventional surveying techniques. The base station determines ranges to GNSS satellites in view by utilising two methods: ATNS/HO/C09/30/02/01 Page 75 of July 2010

76 Using the code-based positioning technique described earlier; or Using the (precisely) known locations of the base station and the satellites, the location of the satellites being determined from the precisely known orbit ephemerides and satellite time. The base station compares the ranges. Differences between the ranges can be attributed to satellite ephemeris and clock errors, but mostly to errors associated with atmospheric delays. Base stations send these errors to other receivers (rovers), which incorporate the corrections into their position calculations. Differential positioning requires a data link between base stations and rovers if corrections need to be applied in real-time, and at least four GNSS satellites in view at both the base station and the rovers. The absolute accuracy of the rover s computed position will depend on the absolute accuracy of the base station s position. Since GNSS satellites orbit high above the Earth, the propagation paths from the satellites to the base stations and rovers pass through similar atmospheric conditions, as long as the base station and rovers are not too far apart. Differential GNSS works very well with base-stationto-rover separation of up to tens of kilometres, typically as used by LAAS. The technique referred to as code-based positioning, is where the receiver correlates with and uses the pseudo-random codes transmitted by four or more satellites to determine the ranges to the satellites. From these ranges and knowing where the satellites are, the receiver can establish its position to within a few metres. For applications such as aviation and surveying, higher accuracies are required. Real-Time Kinematic (RTK), a technique that uses carrier-based ranging, provides ranges (and therefore positions) that are orders of magnitude more precise than those available through code-based positioning. RTK techniques are complicated. The basic concept is to reduce and remove errors common to a base station and rover pair, as illustrated in the graphic below. Real-Time Kinematic ATNS/HO/C09/30/02/01 Page 76 of July 2010

77 At a very basic conceptual level, as shown in the graphic above, the range is calculated by determining the number of cycles between the satellite and the rover station, then multiplying this number by the carrier wave length. The calculated ranges still include errors from such sources as satellite clock and ephemerides, and ionospheric and tropospheric delays. To eliminate these errors and to take advantage of the precision of carrier-based measurements, RTK performance requires measurements to be transmitted from the base station to the rover station. A complicated process called ambiguity resolution is needed to determine the number of whole cycles. Rovers determine their position using algorithms that incorporate ambiguity resolution and differential correction. Like DGNSS, the position accuracy achievable by the rover depends on, amongst other things, its distance from the base station (referred to as the baseline ) and the accuracy of the differential corrections. Corrections are as accurate as the known location of the base station and the quality of the base station s satellite observations. Site selection is important for minimising environmental effects such as interference and multipath, as is the quality of the base station and rover receivers and antennae. The geometric arrangement of satellites, as they are presented to the receiver, affects the accuracy of position and time calculations. Receivers will ideally be designed to use signals from available satellites in a manner that minimises this so called dilution of precision (DOP). To illustrate DOP, consider the example shown in the graphic below left, where the satellites being tracked are clustered in a small region of the sky. In this example, intentionally a bit extreme to illustrate the effect of DOP, it is difficult to determine where the ranges intersect. Position is spread over the area of range intersections, an area which is enlarged by range inaccuracies (which can be viewed as a thickening of the range line). As shown in the graphic on the right, the addition of a range measurement to a satellite that is angularly separated from the cluster allows you to determine a fix more precisely. DOP (poor satellite geometry) DOP (improved satellite geometry) ATNS/HO/C09/30/02/01 Page 77 of July 2010

78 Although it is calculated using complex statistical methods, the following can be said about DOP: DOP is a numerical representation of satellite geometry, and it is dependent on the locations of satellites that are visible to the receiver. The smaller the value of DOP, the more precise the result of the time or position calculation. The relationship is shown in the following formula: Inaccuracy of Position Measurement = DOP x Inaccuracy of Range Measurement So, if DOP is very high, the inaccuracy of the position measurement will be much larger than the inaccuracy of the range measurement. DOP can be used as the basis for selecting the satellites on which the position solution will be based; specifically, selecting satellites to minimise DOP for a particular application. A DOP above 6 results in generally unacceptable accuracies for DGPS and RTK operations. DOP varies with time of day and geographic location but, for a fixed position, the geometric presentation of the satellites repeats every day, for GPS. DOP can be calculated without determining the range. All that is needed is the satellite positions and the approximate receiver location. DOP can be expressed as a number of separate elements that define the dilution of precision for a particular type of measurement, for example, HDOP (horizontal dilution of precision), VDOP (vertical dilution of precision), and PDOP (position dilution of precision). These factors are mathematically related. In some cases, for example when satellites are low in the sky, HDOP is low and it will therefore be possible to get a good-to-excellent determination of horizontal position (latitude and longitude), but VDOP may only be adequate for a moderate altitude determination. Similarly, when satellites are clustered high in the sky, VDOP is better than HDOP. When we extend our DOP illustration to three satellites, one way to view dilution of precision is to consider the tetrahedron formed by having the satellites at three corners and the receiver at the fourth, as illustrated graphically on the right. Minimising DOP is not unlike maximising the volume of this tetrahedron. When satellites are tightly clustered and the angle between the satellites is small, the tetrahedron is long and narrow. The volume of the tetrahedron is small and DOP is correspondingly high (undesirable). When the satellites are located near the horizon, the tetrahedron is flat. Again, the volume of the tetrahedron is small and DOP is high. When the satellites are not tightly clustered in the sky or low in elevation, the volume of the tetrahedron approaches a maximum and DOP is at its lowest (desirable). Minimising DOP ATNS/HO/C09/30/02/01 Page 78 of July 2010

79 In Canada and other countries at high latitude, GNSS satellites are lower in the sky, and achieving optimal DOP for some applications, particularly where good VDOP is required, is sometimes a challenge. When there were fewer GNSS satellites, achieving good DOP was sometimes difficult. These difficulties are being reduced with more GNSS constellations and satellites coming on line every year. Applications where the available satellites are low on the horizon or angularly clustered may still expose the user to the pitfalls of DOP. If you know your application will have obstructed conditions, you may want to use a mission planning tool in assist in your flight planning. As discussed, GNSS use signals from orbiting satellites to compute position, time and velocity. GNSS navigation has excellent accuracy provided the antenna has good visibility to the satellites. When the line-of-sight to the satellites is blocked by obstructions such as severe cloud cover, navigation becomes unreliable or impossible. Inertial Navigation System (INS) use rotation and acceleration information from an Inertial Measurement Unit (IMU) to compute accurate Northrop-Grumman LN-100R Embedded INS/GPS position over time. An INS can also solve the attitude (roll, pitch and heading) of a vessel and is not reliant on any external measurement to compute solution. In the absence of external reference, however, the INS solution drifts over time due to accumulating errors in the IMU data. When combined, the two techniques (GNSS and INS) enhance each other to provide a powerful navigation solution. The degree with which the GNSS and INS technologies are integrated varies with product implementation. For example, in tightly coupled solutions, GNSS observations are used directly by the inertial solution to take advantage of available GNSS data, even when only a few satellites are visible (for instance, to reset or adjust the position being input by the INS). Tightly coupled solutions allow feedback of the inertial solution into the GNSS receiver to improve GNSS performance, for example, signal acquisition and convergence time. To summarise, combining GNSS and INS technologies significantly increases opportunities for application development by overcoming the limitations of the individual technologies GNSS Liability In the development of GNSS, liability relating to signal accuracy and continuity is an issue that is often raised; however, there is currently no satisfactory solution to this problem (see note on the next page). Even in regulatory agencies there seems to be confusion about the status of GNSS, but they accept the partial certification of GNSS products and related services. The facts are that GNSS is in use in Civil Aviation today and aircraft are being supplied with related installations and certified to near CAT I levels. However, the use of GNSS in Public Transport Operations still raises concern, largely because of the potential consequences of a GNSS failure. Despite this, liability still appears relatively low on the agenda, since it is widely assumed that these issues will be resolved when appropriate institutional arrangements are put in place by the ICAO. Yet, whether this is a realistic expectation seems very unclear. ATNS/HO/C09/30/02/01 Page 79 of July 2010

80 Note: The liability issues regarding signal accuracy and continuity is currently addressed through augmentation requirements. This is seen as the only effective means of addressing this issue. GNSS raises technical, commercial, political, military, institutional and legal issues. There are many factors that must be taken into account in order to navigate through the potential minefield that lies in the path of user airliner, airports, ATM providers, manufacturers and individual States as they make strategic decisions that will affect their businesses in generations to come. Issues such as liability, certification, etc. are not just purely altruistic considerations. GNSS is not a system designed solely or specifically for civil aviation. GNSS has many wide ranging applications across all industry sectors and its applications are not just limited to navigation. Indeed, no Civil Aviation Authority or group of CAAs could muster even a tiny fraction of the resources that are required to launch a GNSS. The list of applications and the value of these applications is so great, that the civil aviation market is actually small by comparison, but still very large. This is one of the keys to the problem: GNSS is a generic service of huge commercial significance. The ICAO generally requires its members to accept the certification given by other States to its own navigation services and that the ICAO members accept the certification given by a member State to its registered aircraft and licensed crew. The ICAO is setting standards for both GNSS and GNSS-based services. These standards naturally assumed a GPS-like service. Thus the ICAO is essentially retro-fitting standards to an existing service (and assuming some upgrading of those services). Theoretically speaking, the ICAO s role is simply to set safety and interoperability standards. In reality, the ICAO s actual role in GNSS standardisation is a little anomalous, as it appears to be taking a lead (in defining standards) when so many other sectors have a possibly greater interest. This is, in part, based on the assumption that aviation is the most demanding user in safety. Indeed, many have assumed that GNSS would somehow be approved by the ICAO; however, this UN Institution has no power or precedent for giving any approval that would be legally effective. The ICAO is more a forum for agreeing common standards and settling relations on civil aviation matters between its members. It is not an Agency with any delegated power to carry out approvals; these are the sovereign responsibilities of the member States. In reality, the ICAO concentrates on the interoperability of GNSS (to prevent divergent satellite navigation systems) and the safety of augmentation systems (provided by civil aviation). However, legal liability has to be assured in some way to protect the interests of the civil community in the event of a serious GNSS failure. Conversely, steps would also have to be taken to protect a GNSS provider from hostile legal measures following a major accident or disaster linked to its services. ATNS/HO/C09/30/02/01 Page 80 of July 2010

81 Legal arrangements should be made for GNSS service providers in order to limit or indemnify it against loss or interruptions in service. If an accident were attributable to a GNSS failure, then this may lead to modifications to GNSS or restrictions in its use. In order to provide the necessary assurances required for GNSS operations, a certain level of service will have to be guaranteed and this service level must then be bolstered by augmentation systems. The ICAO ensures interoperability between GNSS services and specifies safety standards for augmentation systems for civil aviation applications. Consequently, technical liability of GNSS cannot be effectively traceable or enforceable; rather, the emphasis is on augmentations systems, with certification remaining the prerogative of a State. 2.4 Description of Receiver The primary components of the GNSS user segment are antennae and receivers, as shown in the graphic on the right. Depending on the application, antennae and receivers may be physically separate or they may be integrated into one assembly. GNSS antennae receive the radio signals that are transmitted by the GNSS satellites and send these signals to the receivers. GNSS User Equipment GNSS antennae are available in a range of shapes, sizes and performances. The antenna is selected based on the application. While a large antenna may be appropriate for a base station, a low-profile aerodynamic antenna may be more suitable for aircraft installations. Receivers process the satellite signals recovered by the antenna to calculate position and time. Receivers may be designated to use signals from one GNSS constellation or from more than one GNSS constellation. As with antennae, receivers may be packaged for a particular application, such as aviation or agriculture. However, as with any other item of avionics equipment, a GNSS receiver is required to be of an approved type and to be installed ATNS/HO/C09/30/02/01 Page 81 of July 2010

82 in accordance with specific criteria. Any installation should be validated by a series of tests, measurements (calibration) and inspections. A typical GNSS receiver/display used in aviation GNSS navigation equipment must have US FAA Technical Standard Order (TSO) C-129 authorisation. (See SA-CATS Communication Equipment.) Display A GNSS avionics system may typically be an integrated, panel-mount, IFR navigation/ communication (NavComm) system. Although various products are available, they mostly have the same basic display functions. When using a GNSS NavComm system for the first time, it is recommended that the aircraft be moved to a location that is well clear of any buildings and other aircraft so that the unit can collect satellite data without interruption. The basic display and primary functions discussed in this section is that of the Garmin GNS430. It is however important to note that the specific user manual for each NavComm system be referred to prior to using the system. The key and knob descriptions provide a general overview of the primary function(s) for each key and knob. Data is entered using the large and small knobs. Garmin GNS430 ATNS/HO/C09/30/02/01 Page 82 of July 2010

83 Left-hand keys and knobs include: The COM Power/Volume knob which controls unit power and communications radio volume. Press momentarily to disable automatic squelch control. The VLOC Volume knob which controls audio volume for the selected VOR/Localiser frequency. Press momentarily to enable/disable the ident tone. The large left knob (COM/VLOC) which is used to tune the megahertz (MHz) value of the standby frequency for the communications transceiver (COM) or the VLOC receiver, whichever is currently selected by the tuning cursor. The small left knob (COM/VLOC) which is used to tune the kilohertz (KHz) value of the standby frequency for the communications transceiver (COM) or the VLOC receiver, whichever is currently selected by the tuning cursor. Press this knob momentarily to toggle the tuning cursor between COM and VLOC frequency fields. The COM flip-flop key which is used to swap the active and standby COM frequencies. Press and hold to select emergency channel ( MHz). The VLOC flip-flop key which is used to swap the active and standby VLOC frequencies (i.e., make the selected standby frequency active). ATNS/HO/C09/30/02/01 Page 83 of July 2010

84 The right-hand keys and knobs include: The RNG key which allows the pilot to select the desired map range. Use the up arrow to zoom out to a larger area, or the down arrow to zoom in to a smaller area. The Direct-to key which provides access to the direct-to function that allows the pilot to enter a destination waypoint and establishes a direct course to the selected destination. The MENU key which displays a context-sensitive list of options. This options list allows the pilot to access additional features or make settings changes which relate to the currently displayed page. The CLR key which is used to erase information, remove map detail, or to cancel an entry. Press and hold the CLR key to immediately display the Default NAV page. The ENT key which is used to approve an operation or complete data entry. It is also used to confirm information, such as during power on. The large right knob which is used to select between various page groups: NAV, WPT, AUX or NRST. With the on-screen cursor enabled, the large right knob allows the pilot to move the cursor about the page. The large right knob is also used to move the target pointer right (turn clockwise) or left (counter-clockwise) when the map panning function is active. The small right knob which is used to select between the various pages within one of the groups listed above. Press this knob momentarily to display the on-screen cursor. The cursor allows the pilot to enter data and/or make a selection from a list of options. When entering data, the small knob is used to select the desired letter or number and the large knob is used to move to the next character space. The small right knob is also used to move the target pointer up (turn clockwise) or down (counter-clockwise) when the map panning function is active. The bottom row keys include: The CDI key that is used to toggle which navigation source (GPS or V/LOC) provides output to an external HSI or CDI. The OBS key which is used to select manual or automatic sequencing of waypoints. Pressing the OBS key selects OBS mode, which retains the current active to waypoint as the navigation reference even after passing the waypoint (i.e., prevents sequencing to the next waypoint). Pressing the OBS key again returns the unit to normal operation, with automatic sequencing of waypoints. When OBS mode is selected, the pilot may set the desired course to/from a waypoint using the Select OBS Course pop-up window, or an external OBS selector on the HSI or CDI. The MSG key which is used to view system messages and to alert the pilot to important warning and requirements. ATNS/HO/C09/30/02/01 Page 84 of July 2010

85 The FPL key which allows the pilot to create, edit, activate and invert flight plans, as well as access approaches, departures and arrivals. A closets point to flight plan feature is also available from the FPL key. The PROC key which allows the pilot to select and remove approaches, departures and arrivals from the flight plan. When using a flight plan, available procedures for the departure and/or arrival airport are offered automatically. Alternatively the pilot may select the desired airport, then the desired procedure. The unit s display is divided into separate windows (or screen areas), including a COM window, VLOC window and a GPS window. Unit display windows Functionality Although the functionality of GNSS receivers (especially when it is an integrated NavComm system) is comprehensive, only the basic functions related to the satellite/receiver interaction will be discussed. Once again the Garmin GNS430 will be used as an example. The Satellite Status Page appears as the unit attempts to collect satellite information. When an Acquiring status is displayed on the Satellite Status page, the signal strengths of any satellite received appear as bar graph readings. This is a good indication that the unit is receiving signals and a position fix is being determined. Following the first-time use if the unit, the time required for a position fix varies, usually from one to two minutes. If the unit can only obtain enough satellites for 2-D navigation (i.e. no altitude), the unit uses the altitude provided by the altitude encoder (if one is connected). The INTEG annunciator (bottom left corner of the screen) indicates that satellite coverage is insufficient to pass built-in integrity monitoring tests. In the example graphic shown below, not enough satellites are being received to determine a position. The Satellite Status page shows the ID numbers for the satellites and the relative signal strength of each satellite received (as a bar graph reading). Searching Sky indicates that satellite almanac data is not available or has expired (if the unit has not been used for six months or more). This means the unit is acquiring satellite data to establish almanac and satellite orbit information, which can take five to ten minutes. The data is re-collected from the first available satellite. The Satellite Status Page displays a Search Sky status, and the message annunciator (MSG), above the MSG key also flashes to alert the pilot of system message, Searching the sky (to view a system message, press the MSG key). ATNS/HO/C09/30/02/01 Page 85 of July 2010

86 Satellite Status Page Page Message The Satellite Status Page also provides a visual reference of GPS receiver functions, including current satellite coverage, GPS receiver status and position accuracy. This page is also helpful in troubleshooting weak (or missing) signal levels due to poor satellite coverage or installation problems. Satellite Status Page Annotations As the GPS receiver locks onto satellites, a signal bar appears for each satellite in view, with the appropriate satellite number underneath each bar. The progress of satellite acquisition is shown in three stages: No signal strength bar the receiver is looking for the satellites indicated; Hollow signal strength bars the receiver has found the satellite(s) and is collecting data; Solid signal strength bars the receiver has collected the necessary data and the satellite(s) is ready for use. Chequered signal strength bars Excluded satellites. The sky view display (at top left corner of the page) shows which satellites are currently in view, and where they are. The outer circle of the sky view represents the horizon (with north ATNS/HO/C09/30/02/01 Page 86 of July 2010

87 at top of the page); the inner circle 45 above the horizon; and the centre point directly overhead. Remember that each satellite has a 30- second data transmission that must be collected (hollow signal strength) before the satellite may be used for navigation (solid signal strength). Once the receiver has determined the present position the unit indicates position, track and ground speed on the other navigation pages. Hollow signal strength bars The Satellite Status Page also indicates the accuracy of the position fix using estimated position error (EPE), dilution of precision (DOP) and horizontal uncertainty level (HUL) figures. DOP measures satellite geometry quality (i.e., number of satellites received and where they are relative to each other) on a scale from one to ten. The lowest numbers are the best accuracy and the highest numbers are the worst. EPE uses DOP and other factors to calculate a horizontal position error. When so authorised, a GNSS receiver may provide non-precision approach guidance. Some receivers may also be used as a supplemental aid for precision approaches, but if not appropriately authorised, the localiser and glide slope receivers must be used for primary approach course guidance. Approaches designed specifically for GNSS are often very simple, and don t require overflying a VOR or NDB. Many non-precision approaches have GPS overlays to allow the pilot to fly an existing procedure (VOR, VOR/DME, NDB, RNAV, etc.) more accurately using GNSS. a. Fault Detection and Exclusion (FDE). FDE consists of two distinct parts: fault detection and fault exclusion. Fault detection (RAIM) detects the presence of an unacceptable large pseudo-range error (and presumably, position error) for a given mode of flight or a satellite failure which can affect navigation. Fault detection is synonymous with RAIM (Receiver Autonomous Integrity Monitoring). Upon detection of a fault, fault exclusion follows and excludes the source of the unacceptable large pseudo-range error, thereby allowing navigation to return to normal without an interruption in service. FDE functionality is provided for oceanic, en-route, terminal and non-precision approach phases of flight. The FDE functionality adheres to the missed alert probability, false alert probability and failed exclusion probability specified by TSO-C145a/C146a. FDE requires no pilot interaction during flight, but predicting the capability of the GNSS constellation to provide service during a flight is done by the pilot prior to departure. FDE prediction allows the pilot to specify the planned departure date/time, route type, ground speed, ground speed variation and maximum allowable outage. When provided through NOTAM or other sources, GNSS satellites with known failures can be excluded through the prediction programme s setup function. On most GNSS receivers, the pilot can view the information related to FDE operation. The image below shows satellite number 9 exclusion during the oceanic phase of flight. In addition to EPE and DOP, the HUL field displays a 99% confidence level that the aircraft position is within a circle with a radius of the value (0.05 NM) displayed in the HUL field. ATNS/HO/C09/30/02/01 Page 87 of July 2010

88 Satellite Status Page Integrity Alerts As mentioned before, RAIM is the technology developed to assess the integrity of GNSS signals in a receiver system. It is of special importance in a safety-critical GNSS application, such as aviation or marine navigation. RAIM detects faults with redundant GNSS pseudo-range measurements. That means, when more satellites are available than needed to produce a position fix, the extra pseudo-ranges should all be consistent with the computed position. A pseudo-range differing significantly from the expected value may indicate a fault with the associated satellite (such as clock failure) or another signal integrity problem (such as ionospheric dispersion). The basic GNSS receiver has three modes of operation; en-route (oceanic), terminal and approach mode. The RAIM alert limits are automatically coupled to the receiver modes are set to 2.0 NM (±3.7 km), 1.0 NM (1.9 km) and 0.3 NM (0.6 km) respectively. a. Constellation Alerts. Ephemeris prediction errors are errors in the declared position of a satellite (as transmitted in the navigation data message). In other words; the satellite wasn t where the system said it was when you made a measurement on its signal. Radial and cross-track errors contribute to ephemeris errors. Ephemeris corrections are calculated using a curve-fit of the control segment s best prediction of each satellite s position at the time of an upload and contain inherent errors. In addition, the errors tend to grow over time from the last control segment navigation data upload. The constellation errors will be made visible to the user by FDE. b. Receiver Related Alerts. As mentioned before, there are a number of manufacturers of basic GNSS receivers on the market and each employs a different method of interface. It is therefore advisable for flight crews to become thoroughly familiar with the operation of their particular receiver prior to ATNS/HO/C09/30/02/01 Page 88 of July 2010

89 using it in flight operations. The equipment must be operated in accordance with the provisions of the applicable aircraft operating manual. It is also advisable to have one of the appropriate checklists available on-board the aircraft for easy reference in the sequential loading and operation of the equipment. The CDI sensitivity is automatically coupled to the operating mode of the receiver and is set to 5.0 NM (±9.3 km), 1.0 NM (1.9 km) or 0.3 NM (0.6 km) for en-route, terminal and approach respectively. Although a manual selection for CDI sensitivity is available, overriding and automatically selected CDI sensitivity during an approach will cancel approach mode. Navigation display with CDI and Route Information The failures caused by the GNSS receiver can have two consequences on navigation system performance, which are the interruption of the information provided to the user or the output of misleading information. Neither of these events is accounted for in the signal-in-space requirement. The nominal error of the GNSS aircraft element is determined by receiver noise, interference, and multi-path and tropospheric model residual errors. ATNS/HO/C09/30/02/01 Page 89 of July 2010

90 2.5 NAVSTAR GPS (Navigation Signal Timing and Ranging Global Positioning System) GPS was the first global navigation satellite system. GPS (or NAVSTAR, as it is officially called) satellites were first launched in the late 1970 s and early 1980 s for the US Department of Defence. Since then, several generations (referred to as Blocks ) of GPS satellites have been launched. Initially, GPS was available only for military use but in 1983, a decision was made to extend GPS to civilian use. The GPS constellation is illustrated in the graphic below: The NAVSTAR GPS Constellation The GPS space segment is summarised in the table below. The orbit period of each satellite is approximately 12 hours, so this provides a GPS receiver with at least six satellites in view from any point on the Earth, under open-sky conditions. Table: GPS Satellite Constellation Satellites 21 plus 3 spare Orbital planes 6 Orbit inclination 55⁰ Orbit radius km ATNS/HO/C09/30/02/01 Page 90 of July 2010

91 A GPS satellite orbit is illustrated in the graphic on the right. GPS satellites continually broadcast their identification, ranging signals, satellite status and corrected ephemerides (orbit parameters). The satellites are identified either by their Space Vehicle Number (SVN) or their Pseudo-Random code Number (PRN). GPS Satellite Orbit The table below provides further information on GPS signals. GPS signals are based on CDMA (Code Division Multiple Access) technology. GPS Signal Characteristics Designation Frequency Description L1 L2 L MHz MHz MHz L1 is modulated by the C/A code (Coarse/Acquisition) and the P-code (Precision) which is encrypted for military and other authorised users. L2 is modulated by the P-code and, beginning with Block IIR-M satellites, the L2C (civilian) code. L2C, is considered under development and forms part of the GPS modernisation process (discussed at a later stage). At the moment, L5 is available for demonstration on one GPS satellite, which is also considered part of the GPS modernisation process (discussed at a later stage). The GPS control segment consists of a master control station (and a back-up master control station) and monitor stations throughout the world, as shown in the graphic below. Four monitor stations were implemented early in the NAVSTAR programme, and then six more NGA (National Geospatial Intelligence Agency, also part of the US Department of Defence) stations were added in ATNS/HO/C09/30/02/01 Page 91 of July 2010

92 The monitor stations track the satellites via their broadcast signals, which contain satellite ephemeris data, ranging signals, clock data and almanac data. These signals are passed to the master control station where the ephemerides are re-calculated. The resulting ephemeride and timing corrections are transmitted back up to the satellites through data up-loading stations. GPS Control Segment GPS reached Fully Operational Capability in In 2000, a project was initiated to modernise the GPS space and ground segments, to take advantage of new technologies and user requirements. Space segment modernisation has included new signals, as well as improvements in atomic clock accuracy, satellite signal strength and reliability. Control segment modernisation includes improved ionospheric and tropospheric modelling and in-orbit accuracy, and additional monitoring stations. User requirement has also evolved, to take advantage of space and control segments improvement. The latest generation of GPS satellites has the capability to transmit a new civilian signal, designated L2C. Once operational, L2C will ensure the accessibility of two civilian codes. L2C will be easier for the user segment to track and it will provide improved navigation accuracy. It will also provide the ability to directly measure and remove ionospheric delay error for a particular satellite, using the civilian signals on both L1 and L2. The US has started implementing a third civil GPS frequency (L5) at MHz. The first NAVSTAR GPS satellite to transmit L5, on a demonstration basis, was launched in The benefits of the L5 signal include meeting the requirements for critical safety-of-life applications such as that needed for civil aviation, and providing improved ionospheric correction, signal redundancy, improved signal accuracy and improved interference rejection. In addition to the new L2C and L5 signals, GPS satellite modernisation includes a new military signal and an improved L1C which will be backward compatible with L1 and which will provide greater civilian interoperability with Galileo. ATNS/HO/C09/30/02/01 Page 92 of July 2010

93 2.6 GLONASS (Global Navigation Satellite System) GLObal naya NAvigatsionnaya Sputnikovaya Sistema or translated into English as GLObal NAvigation Satellite System is a radio-based satellite navigation system, developed by the former Soviet Union as an experimental military communications system during the 1970 s. When the Cold War ended, the Soviet Union recognised that GLONASS had commercial applications, through the system s ability to transmit weather broadcasts, communications, navigation and reconnaissance data. The first GLONASS satellite was launched in 1982 and the system was declared fully operational in After a period where GLONASS performance declined, Russia committed to bringing the system up to the required minimum of 18 satellites. The Russian government set 2011 as the date for full deployment of the 24-satellite constellation and has ensured that the necessary financial support will be there to meet this date. GLONASS satellites have evolved since the first ones were launched. The latest generation, GLONASS-M satellite is shown in the graphic on the right. GLONASS-M Satellite in Final Manufacturing The GLONASS constellation provides visibility to a variable number of satellites, depending on your location. A minimum of four satellites in view allows a GLONASS receiver to compute its position in three dimensions and to synchronise with system time. The GLONASS space segment is summarised in the table below. Table: GPS Satellite Constellation Satellites 21 plus 3 spare Orbital planes 3 Orbit inclination 64.8⁰ Orbit radius km When complete, the GLONASS space segment will consist of 24 satellites in three orbital planes, with eight satellites per plane. The GLONASS constellation geometry repeats about once every eight days. The orbit period of each satellite is approximately 8/17 of a sidereal day so that, after eight sidereal days, the GLONASS satellites have completed exactly 17 orbital revolutions. Each orbital plane contains eight exactly spaced satellites. One of the satellites will be at the same spot in the sky at the same sidereal time each day. The satellites are placed into nominally circular orbits with target inclinations of 64.8 and an orbital radius of km, about km lower than GPS satellites. ATNS/HO/C09/30/02/01 Page 93 of July 2010

94 The GLONASS satellite signal identifies the satellite and includes: Positioning, velocity and acceleration information for computing satellite locations. Satellite health information. Offset of GLONASS time from UTC (SU) formerly Soviet Union and now Russia. Almanac of all other GLONASS satellites. The GLONASS control segment consists of the system control centre and a network of command tracking stations across Russia. The GLONASS control segment, similar to that of GPS, monitors the status of satellites, determines the ephemeride corrections, and satellite clock offsets with respect to GLONASS time and UTC (Coordinated Universal Time). Twice a day, it uploads corrections to the satellites. The table below summarises the GLONASS signals. GLONASS Signal Characteristics Designation Frequency Description L1 L MHz MHz L1 is modulated by the HP (high precision) and the SP (standard precision) signals. L2 is modulated by the HP and SP signals. The SP signal is identical to that transmitted on L1. GLONASS satellites each transmit on slightly different L1 and L2 frequencies, with the P-code (HP code) on both L1 and L2, and the C/A code (SP code), on L1 (all satellites) and L2 (most satellites). GLONASS satellites transmit the same code format at different frequencies, a technique known as FDMA, for frequency division multiple access. Note that this is a different technique from that used by GPS. GLONASS signals have the same polarisation (orientation of the electromagnetic waves) as GPS signals, and have comparable signal strength. The GLONASS system is based on 24 satellites using 12 frequencies. It achieves this by having antipodal satellites transmitting on the same frequency. Antipodal satellites are in the same orbital plane but are separated by 180⁰. The paired satellites can transmit on the same frequency because they will never appear at the same time in view of a receiver on the Earth s surface as shown in the graphic on the right. GLONASS Antipodal Satellites ATNS/HO/C09/30/02/01 Page 94 of July 2010

95 The use of GLONASS in addition to GPS, results in there being a larger number of satellites in the field of view, which has the following benefits: Reduced signal acquisition time; Improved position and time accuracy; Reduction of problems caused by obstructions such as buildings and foliage; Improved spatial distribution of visible satellites, resulting in improved dilution of precision (discussed at a later stage). To determine a position in GPS-only mode, a receiver must track a minimum of four satellites. In combined GPS/GLONASS mode, the receiver must track five satellites, at least one of which must be a GLONASS satellite so that the receiver can determine the GPS/GLONASS time offset. With the availability of combined GPS/GLONASS receivers, users have access to a satellite combined system with over 40 satellites. Performance in urban canyons and other locations with restricted visibility improves as more satellites are accessible by the receiver. Combined GPS/GLONASS receiver 2.7 GALILEO (The name given to the European Global Navigation Satellite System) Galileo, Europe s planned global navigation satellite system, will provide a highly accurate and guaranteed global positioning system under civilian control. The United States and European Union have been co-operating since 2004 to ensure that GPS and Galileo are compatible and interoperable at the user level. By offering dual frequencies as standard, Galileo will deliver realtime positioning accuracy down to the metre range, previously not achievable by a publicly available system. Galileo will guarantee availability of service under all but the most extreme circumstances and it will inform users within seconds of a failure of any satellite. This will make it suitable for applications where safety is crucial, such as in air and ground transport. The first experimental Galileo satellite (GIOVE-A), part of the Galileo System Test Bed (GSTB) was launched in December The purpose of this experimental satellite is to characterise critical Galileo technologies, which are already in development under European Space Agency (ESA) contracts. Preparing to launch the Soyuz-FG rocket with the Galileo satellite ATNS/HO/C09/30/02/01 Page 95 of July 2010

96 Four operational satellites are planned to be launched in the time frame to validate the basic Galileo space and ground segment. Once this In-Orbit Validation (IOV) phase has been completed, the remaining satellites will be launched, with plans to reach Full Operational Capability (FOC) likely sometime after The Galileo space segment is summarised in the table below. Table: GPS Satellite Constellation Satellites 27 operational and 3 active spares Orbital planes 3 Orbit inclination 56⁰ Orbit radius km Once the constellation is operational, Galileo navigational signals will provide coverage at all latitudes. The large number of satellites, together with the optimisation of the constellation and the availability of the three active spare satellites, will ensure that the loss of one satellite has no discernable effect on the user segment. Two Galileo Control Centres (GCC), which are to be located in Europe, will control the satellites. Data recovered by a global network of twenty Galileo Sensor Stations (GSS) will be sent to the GCC through a redundant communications network. The GCC will use data from the sensor stations to compute integrity information and to synchronise satellite time with ground station clocks. Control centres will communicate with the satellites through up-link stations, which will be installed around the world. Galileo will provide a global Search and Rescue (SAR) function, based on the operational search and rescue satellite-aided Cospas-Sarsat system. To do this, each Galileo satellite will be equipped with a transponder that will transfer distress signals to the Rescue Co-ordination Centre (RCC), which will then initiate the rescue operation. At the same time, the system will provide a signal to the user, informing them that their situation has been detected and that help is underway. This latter feature is new and is considered a major upgrade over existing systems, which do not provide user feedback. Five Galileo services are proposed, as summarised in the table below. Table: Galileo Services Service Free Open Service (OS) High reliable Commercial Service (CS) Safety-of-Life Service (SOL) Description Provides positioning, navigation and precise timing service. It will be available for use by any person with a Galileo receiver. No authorisation will be required to access this service. Galileo is expected to be similar to GPS in this respect. Service providers can provide added-value services, for which they can charge the end customer. The CS signal will contain data relating to these additional commercial services. Improves on OS by providing timely warnings to users when it fails to meet certain margins of accuracy. A service guarantee will likely be provided for this service. ATNS/HO/C09/30/02/01 Page 96 of July 2010

97 Service Government encrypted Public Regulated Service (PRS) Search and Rescue Service (SAR) Description Highly encrypted restricted-access service offered to government agencies that require a high availability navigation signal. Public service designed to support search and rescue operations, which will make it possible to locate people and vehicles in distress. 2.8 Other Navigation Satellite Systems China The Beidou Navigation System (or Beidou Satellite Navigation and Positioning System) is a project by China to establish an independent satellite navigation system. The current Beidou-1 system (made up of four satellites) is experimental and has limited coverage and application. However, China has started the implementation of a GNSS known as Compass or Beidou-2. The initial system will provide regional coverage. The target is that this be followed after 2015 with the implementation of a constellation of GEO (geostationary orbit) and MEO (Medium Earth Orbit) satellites that will provide global coverage, as shown in the table below: Table: Planned Compass Satellite Constellation Satellites 35, a combination of 5 GEO and 30 MEO Orbital planes 6 Orbit inclination 55⁰ Orbit radius km The Beidou Navigation System is named after the Big Dipper constellation, which is known in Chinese as Běidǒu. The name literally means "Northern Dipper", the name given by Chinese astronomers to the seven brightest stars of Ursa Major or the Great Bear constellation. Historically, this set of stars was used in navigation to locate the North Star Polaris. As such, Beidou also serves as a metaphor for the purpose of the satellite navigation system. Unlike the GPS, GLONASS and Galileo systems, which use medium Earth orbit (MEO) satellites, Beidou-1 uses satellites in geostationary orbit (GEO). This means that the system does not require a large constellation of satellites, but it also limits the coverage areas on Earth where the satellites are visible. The area that can be serviced is from 70 E to 140 E and from 5 N to 55 N. ATNS/HO/C09/30/02/01 Page 97 of July 2010

98 Coverage Polygon of Beidou-1 As mentioned above, the Beidou-1 satellites (1A, 1B, 1C and 1D), were designed as experimental satellites. The new system (Compass or Beidou-2) will be a constellation of 35 satellites, which include five geostationary orbit satellites, for backward compatibility with Beidou-1, and 30 medium Earth orbit satellites, that will offer complete coverage of the globe. There will be two levels of service provided; free service for those in China, and licensed service for the military: The free service will have a 10-metre location-tracking accuracy, will synchronise clocks with an accuracy of 50 ns, and measure speeds within 0.2 m/s. The licensed service will be more accurate than the free service, can be used for communication, and will supply information about the status to the users. Three satellites for Compass have been launched in 2007, 2009 and also early in In the next few years, China plans to continue setting up the system for global operation from 2017 with 30 satellites. Regional operation within Asia Pacific would be completed with more than 10 satellites in late Table: Beidou-1 and Compass Satellites Date Launcher Satellite Orbit Usable 31/10/2000 LM-3A Beidou-1A GEO 140 E Unclear 21/12/2000 LM-3A Beidou-1B GEO 80 E Unclear 25/05/2003 LM-3A Beidou-1C GEO E Unclear 03/02/2007 LM-3A Beidou-1D De-orbited No 14/04/2007 LM-3A Compass-M1 MEO km Yes 15/04/2009 LM-3C Compass-G2 GEO drifting No 17/01/2010 LM-3C Compass-G1 GEO E Yes ATNS/HO/C09/30/02/01 Page 98 of July 2010

99 The frequencies for Compass are allocated in four bands: E1, E2, E5B and E6; and overlap with Galileo. The overlapping is convenient from a receiver design point of view, but it does raise the issues of inter-system interference, especially within E1 and E2 bands, which are allocated for Galileo s publicly-regulated service. However, under International Telecommunications Union (ITU) policies, the first nation to start broadcasting in a specific frequency will have priority to that frequency, and any subsequent users will be required to obtain permission prior to using that frequency, and otherwise ensure that their broadcasts do not interfere with the original nation's broadcasts. It now appears that Chinese Compass satellites will start transmitting in the E1, E2, E5B, and E6 bands before Europe's Galileo satellites and thus have primary rights to these frequency ranges. Galileo, GPS and Compass Frequency Allocation India The Indian Regional Navigation Satellite System (IRNSS) is an autonomous regional satellite system being developed by Indian Space Research Organisation, which would be under total control of the Indian government. The government approved the project in May 2006, with the intention of the system to be completed and implemented by It will consist of a constellation of seven navigation satellites. The first satellite, of the proposed constellation, is expected to be launched in the last quarter of 2011 with subsequent six months periodic launches taking place. It means the IRNSS will be optimally functional by The proposed system would consist of a constellation of seven satellites and a support ground segment. Three of the satellites in the constellation will be placed in geostationary orbit. These GEOs will be located at 34 E, 83 E and 132 E. These satellites will orbit with a km apogee and a 250 km perigee inclined at 29. Two of the satellites will cross the equator at 55 E and two at 111 E. Such an arrangement would mean all seven satellites would have continuous radio visibility with Indian control stations. The satellite payloads would consist of atomic clocks and electronic equipment to generate the navigation signals. ATNS/HO/C09/30/02/01 Page 99 of July 2010

100 Schematic of Proposed IRNSS Deployment The navigation signals would be transmitted in the S-band frequency (2 4 GHz) and broadcast through a phased array antennae to maintain required coverage and signal strength. The system is intended to provide an all-weather absolute position accuracy of better than 7.6 metres throughout India and within a region extending approximately km around it. A goal of complete Indian control has been stated, with the space segment, ground segment and user receivers all being built in India. The ground segment of IRNSS constellation would consist of a Master Control Centre (MCC), ground stations to track and estimate the satellites orbits and ensure the integrity of the network, and additional ground stations to monitor the health of the satellites with the capability of issuing radio commands to the satellites. The MCC would estimate and predict the position of all IRNSS satellites, calculate integrity, make necessary ionospheric and clock corrections and run the navigation software. In pursuit of a highly independent system, an Indian standard time infrastructure would also be established Japan The Quasi-Zenith Satellite System (QSSS), or Juntencho in Japanese, is a proposed threesatellite regional time transfer system and enhancement for the GPS that will be receivable within Japan. Full operational status is expected by 2013, with the first satellite scheduled for launch in QSSS is targeted at mobile applications, to provide communications-based services (video, audio and data) and positioning information. With regards to its positioning service, QSSS would only provide limited accuracy on its own and is not currently required in its specifications to work in a stand-alone mode. As such, it is viewed as a GNSS augmentation service. ATNS/HO/C09/30/02/01 Page 100 of July 2010

101 The satellites would be placed in a periodic Highly Elliptical orbit (HEO). These orbits allow the satellites to dwell for more than 12 hours a day with an elevation above 70 (meaning they appear almost overhead most of the time) and give rise to the term quasi-zenith for which the system is named. As of June 2003, the proposed orbits ranged from 45 inclination with little eccentricity, to 53 with significant eccentricity. QSSS Orbit QSSS can enhance GPS services in two ways: first, availability enhancement, whereby the availability of GPS signals is improved; second, performance enhancement whereby the accuracy and reliability of GPS derived navigation solutions is increased. Because the GPS availability enhancement signals transmitted from the Quasi-Zenith satellites (QSSs) are compatible with modernised GPS signals, and hence interoperability is ensured, the QSSs will transmit the L1C signal, L2C signal and L5 signal. This minimises changes to specifications and receiver designs France Doppler Orbitography and Radio-positioning Integrated by Satellite (DORIS) is a French satellite system used for the determination of satellite orbits (e.g. TOPEX/Poseidon) and for positioning. It uses the Doppler Effect as principle of operation: a so-called beacon is installed on the ground and it emits a radio signal, which is received by the satellite. A frequency shift of the signal occurs that is caused by the movement of the satellite (Doppler Effect). From this observation, satellite orbits, ground positions, as well as other parameters can be derived. There are about stations equally distributed over the Earth which ensures a good coverage for orbit determination. For the installation of a beacon only electricity is required because the station only emits a signal, but does not receive any information. Therefore it is possible to install beacons in remote areas such as the Mount Everest base camp. The best known satellites equipped with DORIS are the two altimetry satellites TOPEX/Poseidon and Jason. They are used to observe the ocean surface as well as currents or wave heights. DORIS contributes to their orbit accuracy of about 2 cm. ATNS/HO/C09/30/02/01 Page 101 of July 2010

102 TOPEX/Poseidon and Jason Satellite Series Other DORIS satellites are the European Remote-Sensing Satellite (ERS) and SPOT (Satellite Pour l Observation de la Terre) satellites. Life-size Model of the ERS-2 Satellite (left) and SPOT-5 Satellite (right) Apart from orbit determination the DORIS observations are used for positioning of ground stations. The accuracy is a bit lower than with GPS, but it still contributes to the International Terrestrial Reference Frame (ITRF). ATNS/HO/C09/30/02/01 Page 102 of July 2010

103 3 ALL WEATHER OPERATION All weather operations refers to the practice of instrument flying (IF) and the associated procedures as applied during flight under instrument flight rules (IFR). An instrument approach or instrument approach procedure (IAP) is a type of air navigation that allows a pilot to fly an aircraft to a position from which a landing may be effected under reduced visibility conditions (known as instrument meteorological conditions or IMC), or to reach visual conditions permitting a visual approach and subsequent landing. IAPs fall into one of two categories. Firstly and also the more commonly used is the pilot interpreted approach procedure (ILS, VOR and NDB approaches). Secondly and used infrequently by civilian commercial operators is the ATC interpreted approach procedure (surveillance radar approach SRA, ground controlled approach GCA and the oldest of them all the VDF cloud brake procedures). Pilot interpreted approaches are classified as either precision or non-precision, depending on the accuracy and capabilities of the navigational aids (NAVAIDs) used. Precision approaches utilise both lateral (localiser) and vertical (glide slope) information. Non-precision approaches provide lateral course information only. The publications depicting instrument approach procedures are called Terminal Procedures, but are commonly referred to by pilots as "approach plates". These documents graphically depict the specific procedure to be followed by a pilot for a particular type of approach to a given runway. They depict prescribed altitudes and headings to be flown, as well as obstacles, terrain, and potentially conflicting airspace. In addition, they also list missed approach procedures and commonly-used radio frequencies. Instrument approaches are generally designed such that a pilot of an aircraft in instrument meteorological conditions (IMC), by the means of radio, GNSS or INS navigation with no assistance from air traffic control, can navigate to the airport, hold in the vicinity of the airport if required, then fly to a position from where sufficient visual reference of the runway may be established to allow landing to be made, or execute a missed approach if the required visual contact with the aerodrome and/or runway periphery is not established. The whole of the approach is defined and published in this way so that instrument approaches may be completed procedurally at airports where air traffic control does not use radar or in the case of radar failure. Instrument approaches generally involve five phases of flight: Arrival: where the pilot navigates to the Initial Approach Fix (IAF: a NAVAID or reporting point), and where holding can take place. Initial Approach: the phase of flight after the IAF, where the pilot commences the navigation of the aircraft to the Final Approach Fix (FAF), a position aligned with the runway, from where a safe controlled descent back towards the airport can be initiated. Intermediate Approach: an additional phase in more complex approaches that may be required to navigate to the FAF. Final approach: between 4 and 12 NMs of straight flight descending at a set rate (usually an angle of between 2.5 and 6⁰). Missed Approach: an optional phase; should the required visual reference for landing not have been obtained at the end of the final approach, this allows the pilot to climb the aircraft to a safe ATNS/HO/C09/30/02/01 Page 103 of July 2010

104 altitude and navigate to a position to hold for weather improvement, from where another approach can be commenced or the decision to divert may be taken. When aircraft are under radar control, air traffic controllers may replace some or all of these phases of the approach with radar vectors to the final approach. This is done to allow traffic levels to be increased from what is possible when a fully procedural service is being provided. It is very common for air traffic controllers to vector aircraft to the final approach aid, e.g. the ILS, which is then used for the final approach. In the case of the rarely-used Ground Controlled Approach, the instrumentation (normally Precision Approach Radar) is on the ground and monitored by a controller, who then issues precise instructions for the adjustment of heading and altitude of the aircraft to the pilot flying the approach. 3.1 Conventional NAVAID Based Procedures There are a number of different procedures available at the moment, all based on conventional NAVAIDs including VDF, NDB, VOR, SRA, ILS, GCA Standard Instrument Departures (SIDs) and Standard Terminal Arrival Routes (STARs) Standard Instrument arrival and departure procedures are designed in such a way that they require aircraft to fly (track) either directly away from or directly to a beacon. Some procedures may even require the pilot to intercept and then follow a DME arc, or whilst tracking towards one beacon, execute a turn at a published DME range and then intercept a track to another beacon. One of the reasons for designing these standard instrument routings is to reduce the need for ATCs to vector aircraft, another reason is to reduce the amount of radio transmissions between ATC and pilot. A STAR usually covers the phase of a flight that lies between the top of descent from cruise or en-route flight and the final approach to a runway for landing. A typical STAR consists of a set of starting points, called transitions, and a description of routes (typically via waypoints) from each of these transitions to a point near a destination airport, upon reaching which the aircraft can join an instrument approach (IAP) or be vectored for a final approach by the approach controller. Sometimes several airports in the same area may share a single STAR, in such cases aircraft destined for any of the airports served by the particular STAR will follow the same arrival route up until reaching the final waypoint, after which they join approaches for their respective destination airports. ATNS/HO/C09/30/02/01 Page 104 of July 2010

105 STARs can be very detailed (as is often the case in Europe), allowing pilots to go from the start of the descent to the final approach entirely on their own once ATC has cleared them for the arrival, or they can be more general (as is often the case in the United States), providing guidance to the pilot which is then supplemented by instructions from ATC. Just like the STAR, a SID is normally developed to reduce both pilot and ATC workload and aims to regulate and streamline the traffic flow out of an airport or area. SIDs are designed to be easy to understand and if possible limited to one page. Although a SID will keep aircraft away from terrain, it is optimised for ATC route of flight and will not always provide the most efficient climb, but aims to strike a balance between obstacle avoidance and airspace considerations The Non-Precision Approach (NPA) The NPA is the oldest type of instrument approach used. Today there are two categories of NPAs, firstly and most commonly used are the pilot interpreted NPAs and secondly, the less frequently used ATC interpreted surveillance radar approach (SRA).The NPA was developed to allow an aircraft to transition from the cruise phase of flight, most often via a descent leg, holding pattern and a final descent leg to a position on final approach from where the aircraft may break cloud, the pilot establish visual contact with the runway and/or the aerodrome environment and affect a landing with visual reference to the ground. The first and most often used, the pilot interpreted NPA, may be based on one of two NAVAIDs, either a NDB or a VOR. These approaches offer only lateral guidance with no form of vertical guidance being offered from the NAVAID itself. For this type of approach the pilot will manage the vertical navigation of the aircraft-based on reference to the barometric altitude (aircraft altimeter) of the aircraft and published crossing altitudes/heights along the NPA. This type of operation results in what is known as a dive and drive approach. This dive and drive procedure has been found to be the single biggest cause of controlled flight into terrain (CFIT) accidents. ATNS/HO/C09/30/02/01 Page 105 of July 2010

106 The SRA dictates that a radar service must be available for this service to be offered to an arriving aircraft. There is also a requirement for specific controller training that must have been completed as well as an approved SRA procedure published in the AIP, before an ATC at a suitably equipped air traffic service unit (ATSU) would be allowed to offer this type of service. Give guidance only in azimuth (lateral) no vertical guidance. By their design, all NPAs suffer from two major drawbacks. The first is that the missed approach point and minimum descent altitude will always leave the aircraft very high with regard to the ideal 3⁰ glide slope and thus very close to the runway threshold. This close and high position requires very aggressive handling to affect a landing but results in an unstable, high rate of descent approach and all this in the last 500 above the runway. This is why this type of approach has resulted in such a disproportionally high number of CFIT accidents as compared to precision approaches The Precision Approach (PA) The NPA, though useful as an early development to enable all weather operation, proved to be limited in its ability to facilitate continued operation in really poor weather conditions. Early on the demand for an approach aid that offered better usability than the NDB or VOR approach lead to the development of what we now know as a precision approach (PA). The PA, like the NPA, was and still is available as either a pilot interpreted (ILS) or ATC interpreted (GCA) approach. In the middle to late forties the ICAO accepted the then new instrument landing system (ILS) as the most effective and reliable method allowing approach and landing operation in condition of low cloud (as low as 200 agl) and poor visibility (as low as 800m) for commercial operation. The ILS is the dominant approach aid at civilian aerodromes while most military installation worldwide has developed and retained GCA capability in tandem with ILS deployment. ATNS/HO/C09/30/02/01 Page 106 of July 2010

107 a. Instrument Landing System (ILS). ILS forms an integral part of AST service delivery, is widely used and will remain widely in use well beyond The reason for this is because the ground and airborne equipment is readily available, relatively cheap to install and maintain and very familiar to all operators. An ILS approach (from the basic CAT I to the most enabling CAT III) although very useful and able to support continued flight operations in extremely poor weather conditions, still have a few fundamental restrictions. One of these restrictions is that an ILS requires the final approach track to be aligned with runway centre line from at least 10 NM out. This means that the use of an ILS in confined areas is problematic (e.g. at aerodromes situated in very mountainous terrain like to Alps). Although the ILS offers an effecting solution during most IMC days, the capability to offer and operate under Cat II and lower minima is very costly and offset against operator profitability often does not make business sense. Operators often choose to make passengers wait, rather than pay for Cat II capability to be maintained for 365 days and used for a few approaches on a few days per year. b. Micro-Wave Landing System (MLS). A microwave landing system (MLS) is an allweather, precision landing system originally intended to replace or supplement instrument landing systems (ILS). MLS has a number of operational advantages, including a wide selection of channels to avoid interference with other nearby airports, excellent performance in all weather, and a small "footprint" at the airports. Although some MLS systems became operational in the 1990s, the widespread deployment initially envisioned by its designers never became a reality. Since its introduction most existing MLS systems in North America have been turned off. The integrity and continuity of service of the MLS signal-in-space does possess the necessary characteristics to support Cat II and Cat III, as does the ILS. MLS continues to be of some interest in Europe, where concerns over the availability of GPS ATNS/HO/C09/30/02/01 Page 107 of July 2010

108 continue to be an issue. A widespread installation in the United Kingdom is currently underway, which included installing MLS receivers on most British Airways aircraft, but the continued deployment of the system is in doubt. NASA operates a similar system called the Microwave Scanning Beam Landing System to land the Space Shuttle. Australia, in 1979 manufactured MLS systems that were subsequently deployed in the US, EU, Taiwan, China and Australia. The CAA in UK developed a version of the MLS which is installed at Heathrow and other airports due to the greater incidence of instrument approaches and Cat II/III weather there. Compared to the existing ILS system, MLS had significant advantages. The antennas were much smaller, due to using a higher frequency signal. They also did not have to be placed at a specific point at the airport, and could "offset" their signals electronically. This made placement at the airports much simpler compared to the large ILS systems, which needs to be placed at the ends of the runways and along the approach path. Another advantage was that the MLS signals covered a very wide fan-shaped area off the end of the runway, allowing controllers to vector aircraft in from a variety of directions or guide aircraft along a segmented approach. In comparison, ILS required the aircraft to fly down a single straight line, requiring controllers to distribute planes along that line. MLS allowed aircraft to approach from whatever direction they were already flying in, as opposed to having to hold before being vectored to "capturing" the ILS signal. This was particularly interesting to larger airports, as it potentially allowed the aircraft to be separated horizontally until much closer to the airport. Similarly in elevation, the fan shape coverage allows for variation in approach angle making MLS particularly suited to aircraft with steep approach angles such as helicopters, fighters and the space shuttle. Unlike ILS, which required a variety of frequencies to broadcast the various signals, MLS used a single frequency, broadcasting the azimuth and altitude information one after the other. This reduced frequency contention, as did the fact that the frequencies used were well away from FM broadcasts, another problem with ILS. Additionally, MLS offered two hundred channels, making the possibility of contention between airports in the same area extremely remote. Finally, the accuracy was greatly improved over ILS. For instance, standard DME equipment used with ILS offered range accuracy of only +/ feet. MLS improved this to +/- 100 ft in what they referred to as DME/P (P for precision), and offered similar improvements in azimuth and altitude. This allowed MLS to guide the extremely accurate CAT III approaches, whereas this normally required expensive ground-based high precision radar. Similar to other precision landing systems, lateral and vertical guidance may be displayed on conventional course deviation indicators or incorporated into multipurpose cockpit displays. Range information can also be displayed by conventional DME indicators and also incorporated into multipurpose displays. 3.2 Continuous Descent Approach (CDA) CDA finds application in two areas, first between TOD and FAF and second between the FAF and Missed approach point or landing. ATNS/HO/C09/30/02/01 Page 108 of July 2010

109 The CDA concept is used during a NPA to replace the dive and drive method of vertical profile management with a continuous descent from the FAF to the missed approach point. This done to reduce the risk of controlled flight into terrain (CFIT) accidents. During the descent from cruise to the FAF the CDA concept is used to save fuel and reduce the noise impact of the flight. To gain the maximum benefit from the application of a CDA, the pilot needs to know the track miles to touch down and that the track to final approach will remain set. In an ideal world this requires that arriving traffic be sequenced and that the arrival rate and sequence be known to ATC and the Flight deck before the descent is commenced. For the CDA concept to work ATC must allow aircraft continuous descend from TOD to touch down. Aircraft RNAV systems are and have been able to calculate TOD based on CDA profile taking aircraft performance into account. 3.3 Non-Conventional NAVAID Based Procedures (RNAV Approaches) The intention with RNAV approaches was to negate the requirement to have aircraft fly directly to or from a groundbased NAVAID or along a DME arc during the descent, approach and landing phases of flight. Aircraft have had the ability to perform RNAV operations from the time the flight navigators were removed from the flight deck, this means from the time the British Comment and American Boeing 707 first flew. At that time the navigation performance accuracy was, undefined, unregulated and wholly misunderstood by ATC. This was the case until the 1980s when operators started demanding to be allowed to develop the RNAV capabilities of the aircraft and ATC was required to improve airspace utilisation. RNAV concepts were first incorporated into oceanic airspace and then later in continental en-route airspace. This brought some benefit to operators and airspace utilisation but also served to highlight the gross inefficiencies of terminal operation. There are a number of problem areas in terms of traditional terminal operations, these include but are not limited to; inconsistent arrival and departure routes which makes fuel planning difficult, increased work load for both ATC and flight crew due to extensive holding followed by incessant vectoring that, most often results in inefficient flight profiles requiring extended downwind legs to be flown in very inefficient configurations resulting in, ATNS/HO/C09/30/02/01 Page 109 of July 2010

110 high fuel burns, extensive noise and environmental pollution and adding to airspace congestion Overlay Procedures Concept Early attempts to improve terminal operations resulted in overlay RNAV procedures being developed that would initially shadow conventional terminal procedures. These overlay RNAV procedures brought no benefit or improvement to the situation and appeared to be a waste of time and effort. The reason why no benefit was gained from this was because these new procedures differed from the conventional procedures only in as much as the definition of the waypoints was changed from using conventional ground-based beacons to using RNAV waypoints. The drive to develop and implement these overlay RNAV procedures had a few fundamental flaws that meant these overlay procedures would never be able to realise the anticipated benefits. To ultimately realise the expected benefits from terminal RNAV procedures the terminal operational concept needed to change completely. The RNAV operation itself needed to be clearly regulated to ensure accuracy, integrity and continuity, the airspace concept needed to clearly define the navigation specification and the ATM system needed to be redefined to allow for and effectively incorporate automated flow management capabilities. One of the fundamental RNAV capabilities that was never employed effectively was the required time of arrival (RTA) capability. The RTA capability combined with the ability of the RNAV system to calculate TOD based on the CDA concept means that the flight deck system is now and has been able for a long time to calculate the most efficient descend profile while being able to fly any published RNAV STAR. ATNS/HO/C09/30/02/01 Page 110 of July 2010

111 3.3.2 Standard Instrument Departures (SIDs) and Standard Terminal Arrival Routes (STARs) RNAV SIDs and STARs, if developed correctly will increase airspace capacity, reduce, if not totally eliminate conflict between arrival and departure routes, reduce both ATC and pilot workload and reduce, if not totally eliminate the need to vector aircraft in terminal airspace. ATNS/HO/C09/30/02/01 Page 111 of July 2010

112 a. Open & Closed Standard Terminal Arrival Routes (STARs). RNAV STARs allow one of two types of terminations. The one is an open termination and the other is a closed termination. An open STAR is simply put a STAR that terminates in ATC vectors being provided onto the final approach segment. This final approach segment is typically a pilot interpreted PA (an ILS). Merging of arrival flows with open loop radar vectors at PARIS CDG, 2002 A closed STAR is one where no ATC vectoring is required, the STAR will place the aircraft onto the ILS through the published procedure. ATNS/HO/C09/30/02/01 Page 112 of July 2010

113 Both the open and closed STAR has a built-in track lengthening or shortening ability, but the actual route that the aircraft will fly while on the STAR will be known to both the ATC and the pilot before the aircraft commences the descent. This route is determined by an automated ATM flow management function. ATNS/HO/C09/30/02/01 Page 113 of July 2010

114 The point merge method; Maintains flexibility to be able to expedite or delay aircraft, Keeps aircraft on Flight Management System trajectory, Maximises runway throughput ATNS/HO/C09/30/02/01 Page 114 of July 2010

115 3.3.3 Sensor Specific Area Navigation (RNAV) Procedures a. RNAV 5 (in Europe referred to and applied as Basic-RNAV aka B-RNAV). B-RNAV requires aircraft conformance to a track keeping accuracy of ± 5 NM for at least 95% of flight time to ensure that the capacity gains are achieved whilst meeting the required safety targets. B-RNAV can be achieved using inputs from VOR/DME, DME/DME or GPS. (INS may be used for up to 2 hours after the last radio beacon or on-ground update. B-RNAV requirements became mandatory in ECAC airspace on 23 April 1998 on the entire ATS route network above FL 95. B-RNAV is already being used on selected routes into and out of terminal airspace in some States. i. What is B-RNAV? RNAV is a method of navigation which permits aircraft operations on any desired flight path within the coverage of station referenced navigation aids or within the limits of the capability of self-contained aids, or a combination of these. Airborne RNAV equipment automatically determines aircraft position by processing data from one or more sensors and guides the aircraft in accordance with appropriate routing instructions. Position can be displayed to the pilot in various ways, most practically in terms of the aircraft position relative to the precomputed desired track. Most RNAV equipment can employ any lateral displacement of the aircraft from the desired track to generate track guidance signals to the auto-pilot. With other less sophisticated RNAV equipment manual corrective action is taken by the pilot. B(asic)-RNAV defines European RNAV operations which satisfy a required track keeping accuracy of ± 5 NM for at least 95% of the flight time. This level of navigation accuracy is comparable with that which can be achieved by conventional navigation techniques on ATC routes defined by VOR/DME, when VORs are less than 100 NM apart. For the determination of aircraft position suitable input data can be derived from the following navigation sources: DME/DME VOR/DME (within 62 NM VOR range) INS (with radio beacon updating or limited to 2 hours use after last on-ground position update) LORAN C (with use limitations) GPS (with use limitations) For ECAC airspace the primary sources of navigation information are VOR/DME, DME/DME and GPS. The availability and continuity of VOR and DME coverage have been calculated for most of Europe and they are considered to be capable of meeting the requirements of the enroute phase of operations. ATNS/HO/C09/30/02/01 Page 115 of July 2010

116 ii. What does B-RNAV offer? B-RNAV operations in ECAC airspace provides a number of advantages over the conventional ground-based navigation, whilst maintaining existing safety standards. These advantages and their related benefits include: (1) improved management in the flow of traffic by repositioning of intersections; (2) more efficient use of available airspace, by means of a more flexible ATS route structure and the application of the Flexible Use of Airspace (FUA) Concept, permitting the establishment of: more direct routes (dual or parallel) to accommodate a greater flow of en-route traffic; bypass routes for aircraft overflying high-density terminal areas; alternative or contingency routes on either a planned or an ad hoc basis; establishment of optimum locations for holding patterns; optimised feeder routes; (3) reduction in flight distances resulting in fuel savings; (4) reduction in the number of ground navigation facilities. All these are easily achievable. One of the main objectives of the initial application of RNAV should be to ensure that full use is made of the existing on board RNAV systems. Many RNAV systems have been fitted for some time and are capable of performance better than RNP 5 accuracy. Simulations demonstrated that capacity gains up to 30% could be achieved only by a uniform application of B-RNAV, in parallel with the revised ATS route network and the implementation of FUA concept. iii. Where and how could B-RNAV be implemented? If implemented in terminal airspace the requirement will be that VOR/DME remains available for reversionary navigation. VOR/DME must also remain available for reversionary navigation on ATS routes in the lower airspace. iv. Where has B-RNAV been implemented? B-RNAV has been implemented throughout the entire ATS Route Network in the ECAC area since 23 April B-RNAV applies to all IFR flights operating in the public transport category, in conformity with the ICAO procedures. In some cases B-RNAV has also been implemented on certain SIDs and STARs provided that: (1) The B-RNAV portion of the route is above Minimum Sector Altitude/Minimum Flight Altitude/Minimum Radar Vectoring Altitude (as appropriate), has been developed in accordance with established PANS-OPS criteria for en-route operations and conforms to B-RNAV en-route design principles. (2) The initial portion of departure procedures is non-rnav up to a conventional fix beyond which the B-RNAV procedure is provided in accordance with the criteria given above. (3) The B-RNAV portion of an arrival route terminates at a conventional fix in accordance with the criteria given above and the arrival is completed by an alternative final approach procedure (most often the conventional ILS), also appropriately approved. ATNS/HO/C09/30/02/01 Page 116 of July 2010

117 (4) Due regard has been taken, during the design process, of the users operating procedures. The National Authorities may designate domestic routes in the lower airspace, which can be used by aircraft which are not B-RNAV capable. Each State should publish appropriate mandatory carriage requirements identifying the airspace within which the mandate prevails. National Administrations are required to publish the coverage of their navigation aids, to notify the status of these aids and to ensure that the co-ordinates of all aids and waypoints are referenced to the WGS-84 geodetic reference system. Manufacturers, operators and database providers are responsible for ensuring that RNAV systems operate in accordance with the WGS-84 system. The specific procedures for B-RNAV operations are incorporated in the ICAO Doc 7030/4 Ed b. Lateral Navigation (LNAV). LNAV refers to navigating over a ground track with guidance from an electronic device which gives the pilot (or autopilot) error indications in the lateral direction only and not in the vertical direction. In aviation lateral navigation is of two guidance types: linear guidance and angular guidance. Linear means that the left and right deviations of the aircraft are available as a distance of the aircraft from the desired ground track to its actual position on either side of the desired track. In angular guidance, the error indication is given in degrees of angle from the desired line relative to a ground-based navigation device. To provide an illustration, as the aircraft approaches the ground device with a constant angular error, its distance to the desired ground line decreases. In the context of aviation instrument approaches, an LNAV approach (one that uses lateral navigation) is implied to be a GNSS navigation signal based approach and to have linear lateral guidance. A VOR based approach will have angular lateral guidance. The approach minimas for LNAV approaches are higher than that of ILS approaches and higher than those for RNAV approaches that incorporate vertical guidance. An aircraft executing an LNAV instrument approach must descend incrementally rather than follow a fixed glide slope. A LNAV approach is a type of 'non-precision' approach. In a precision approach there is electronic vertical (slope) guidance down to a decision altitude (DA). In the case of the non-precision approach, the aircraft can descend only to the minimum descent altitude or MDA. An MDA segment is flown until the airport is in sight and the pilot can land. If the airport is not in sight ATNS/HO/C09/30/02/01 Page 117 of July 2010

118 by the time the pilot reaches a missed approach point (MAP) on the MDA, a missed approach must be initiated. The RNAV implementation of the non-precision LNAV approach (using GNSS as navigation signal source) may only be flown if satellite configuration at the time of the approach will support the accuracy requirement that will allow a full scale course deviation indication of 0.3 nautical miles (about 1800 feet to the left and right or 3600 feet total) from the final approach fix and extending uninterrupted through to the missed approach point. If this sensitivity is not available or is lost, the pilot will be notified by the on-board receiver (via RAIM checking) and must initiate a missed approach or continue with an alternate type of approach using an alternate navigation reference (typically conventional NAVAIDs). c. Barometric Vertical Navigation (Baro-VNAV) and Approach with Vertical Guidance (APV). VNAV in aviation is a function of autopilot which directs vertical movement of aircraft either according to a pre-programmed FMS flight plan during cruise or according to ILS glide slope during an approach. Vertical guidance is given with reference to barometric altitude. VNAV in the sense that the FMS directs altitude according to a flight plan was first introduced on B757 and B767 in 1982, while Autoland (using ILS guidance) has been available since mid-20th century. In the USA Localiser performance with vertical guidance (LPV) are the highest precision GPS (WAAS enabled) instrument approach procedures currently available without specialised aircrew training requirements, such as required navigation performance (RNP). Landing minima are similar to those in an instrument landing system (ILS), that is, a decision altitude of 200 feet and visibility of 1/2 mile. Examples in the USA (from Garmin) are the GNS 480, GNS 430W, 530W, and the Garmin G1000. LPV is designed to provide 16 meter horizontal accuracy and 20 meter vertical accuracy 95 percent of the time. Actual performance has exceeded these levels. WAAS has never been observed to have a vertical error greater than 12 meters in its operational history. As of January 15, 2009 the Federal Aviation Administration has published 1,445 LPV approaches at 793 airports. This is greater than the number of published Category I ILS procedures RNP Procedures (Pre-PBN) a. Baro-VNAV and APV. The baro-vnav navigation system presents the pilot with estimated vertical guidance referenced to a specified vertical path angle (VPA), nominally of 3º. The computed vertical guide is based on the barometric altitude and is specified as a VPA from the reference datum height (RDH). The calculated vertical path is stored in RNAV/RNP system navigation data base as part of the instrument flight procedure specification. For other flight phases, barometric VNAV offers vertical guidance path information that can be defined by vertical angles or altitudes at the procedure fixes. It should be noted that vertical navigation can be performed without VNAV guidance in the initial and intermediate segments of an instrument procedure. It is anticipated that aircraft authorised to conduct RNP authorisation required ATNS/HO/C09/30/02/01 Page 118 of July 2010

119 GNSS Landing System approach (RNP AR APCH) operations would also be considered eligible for the baro-vnav operations NAVAID infrastructure. The procedure design does not have unique infrastructure requirements. This criterion is based upon the use of barometric altimetry by an airborne RNAV/RNP system whose performance capability supports the required operation. The procedure design will have to take into account the functional capabilities required as prescribed by the ICAO. b. GNSS Landing System (GLS). The aviation industry has been developing a positioning and landing system based on a GNSS. These efforts culminated in late 2001, when the ICAO approved an international standard for a landing system based on RNAV using local correction of GNSS data to a level that would support instrument approaches. This work by the ICAO resulted in the ICAO Standards and Recommended Practices (SARPS) that define the characteristics of a GBAS. The GBAS service provides a correction signal that can be used by suitably equipped aircraft as the basis of a GNSS landing system (GLS). The initial SARPS by the ICAO supports an approach service. Future refinements should lead to full low-visibility service (i.e., takeoff, approach, and landing) and low visibility taxi operations. i. Elements of the GLS The GLS consists of three major elements; a GNSS that supports worldwide navigation position fixing, a GBAS facility at each equipped airport that provides local navigation satellite correction signals, and avionics in each aircraft that process and provide guidance and control based on the satellite and GBAS signals (fig.1). The GLS uses a GNSS for the basic positioning service. The GPS constellation already is in place and improvements are planned over the coming decades. The Galileo constellation was scheduled to be available in 2008, but is not yet fully operational. A GBAS service is used for local augmentation of the basic GNSS positioning at or near the relevant airport via a GBAS radio transmitter facility. The GBAS corrections are transmitted from a ground station and can be received by nearby aircraft via a VHF Data Broadcast (VDB) data link. As far as the development of avionics is concerned, Boeing aircraft that are currently being produced contain Multi-Mode Receivers (MMR) that supports conventional ILS and basic GPS operations. For the GLS application the aircraft systems only use satellite information that is supported by correction data received from the GBAS. When the aircraft are relatively ATNS/HO/C09/30/02/01 Page 119 of July 2010

120 Figure 2. GLS Primary Nav. Display close to the GBAS station, the corrections are most effective, and the MMRs can compute a very accurate position. Typical lateral accuracy is expected to be better than or equal to 1 m. ii. GLS Operations A single GBAS ground station typically provides approach and landing service to all runways at the airport where it is installed. The GBAS may even provide limited approach service to nearby airports. Each runway approach direction requires the definition of a final approach segment (FAS) to establish the desired reference path for an approach, landing, and rollout. The FAS data for each approach are determined by the GBAS service provider and typically are verified after installation of the GBAS ground station. One feature that differentiates the GLS from a traditional landing system such as the ILS is the potential for multiple final approach paths, glide slope angles, and missed approach paths for a given runway. Each approach is given a unique identifier for a particular FAS, glide slope, and missed approach combination. FAS data for all approaches supported by the particular GBAS facility are transmitted to the aircraft through the same high-integrity data link as the satellite range correction data (i.e., through the VDB data link). The MMRs process the pseudo range correction and FAS data to produce an ILS-like deviation indication from the final approach path. These deviations are then displayed on the pilot s flight instruments (e.g., Primary Flight Display [PFD]) and are used by aircraft systems such as the flight guidance system (e.g., autopilot and flight director) for landing guidance. The ILS-like implementation of the GLS was selected to support common flight deck and aircraft systems integration for both safety and economic reasons. This implementation helps provide an optimal pilot and system interface while introducing the GLS at a reasonable cost. The use of operational procedures similar to those established for ILS approach and landing systems minimises crew training, facilitates the use of familiar instrument and flight deck procedures, simplifies flight crew operations planning, and ensures consistent use of flight deck displays and annunciations. For example, the source of guidance information (shown on the PFD in fig. 2) is the GLS rather than the ILS. The scaling of the path deviation information on the pilot s displays for a GLS approach can be equivalent to that currently provided for an ILS approach. Hence, the pilot can monitor a GLS approach by using a display that is equivalent to that used during an ILS approach. Figure 2 shows a typical PFD presentation for a GLS approach. The Flight Mode Annunciation on the PFD is GLS for a GLS approach and ILS for an ILS approach. ATNS/HO/C09/30/02/01 Page 120 of July 2010

121 Figure 3 shows a typical GLS approach procedure. The procedure is similar to that used for ILS except for the channel selection method and the GLS-unique identifier. The approach chart is an example of a Boeing flight-test procedure and is similar to a chart that would be used for air carrier operations, with appropriate specification of the landing minima. Figure 4 is an example of a possible future complex approach procedure using area navigation (RNAV), Required Navigation Performance (RNP), and GLS procedures in combination. Pilots could use such procedures to conduct approaches in areas of difficult terrain, in adverse weather, or where significant nearby airspace restrictions are unavoidable. These procedures would combine a RNP transition path to a GLS FAS to the runway. These procedures can also use GBAS position, velocity, and time (PVT) information to improve RNP capability and more accurately deliver the airplane to the FAS. The GBAS is intended to support multiple levels of service to an unlimited number of aircraft within radio range of the VDB data link. Currently, the ICAO has defined two levels of service: Performance Type 1 (PT 1) service and GBAS Positioning Service (GBAS PS). PT 1 service supports ILS-like deviations for an instrument approach. The accuracy, integrity, and continuity of service for the PT 1 level have been specified to be the same as or better than the ICAO standards for an ILS ground station supporting Category I approaches. The PT 1 level was developed to initially support approach and landing operations for Category I instrument approach procedures. However, this level also may support other operations such as guided takeoff and airport surface position determination for low-visibility taxi. The GBAS PS provides for very accurate PVT measurements within the terminal area. This service is intended to support FMS-based RNAV and RNP-based procedures. The improved accuracy will benefit other future uses of GNSS positioning such as Automatic Dependent Surveillance Broadcast and Surface Movement Guidance and Control Systems. The accuracy of the GBAS service may support future safety enhancements such as a high-quality Figure 3. Typical GLS Approach Procedure Figure 3. Typical GLS Approach Procedure ATNS/HO/C09/30/02/01 Page 121 of July 2010

122 electronic taxi map display for pilot use in bad weather. This could help reduce runway incursion incidents and facilitate airport movements in low visibility. The service also may support automated systems for runway incursion detection or alerting. As important as the accuracy of the GBAS service is the integrity monitoring provided by the GBAS facility. Any specific level of RNP operation within GBAS coverage should be more available because the user receivers no longer will require redundant satellites for satellite failure detection (e.g., RAIM). Because the GBAS PS is optional for ground stations under the ICAO standards, some ground stations may only provide PT 1 service. The messages uplinked through the VDB data link indicate whether or not the ground station supports the GBAS PS and specify the level of service for each approach for which a channel number has been assigned. When the GBAS PS is provided, a specific five-digit channel number is assigned to allow selection of a nonapproach-specific GBAS PS from that station. Consequently, the channel selection process allows different users to select different approaches and levels of service. The GBAS PS and the PT 1 service are not exclusive. If the ground station provides the GBAS PS, selecting a channel number associated with any particular approach automatically will enable the GBAS PS service. The receiver provides corrected PVT information to intended aircraft systems as long as the GBAS PS is enabled. ILS-like deviations also are available when the aircraft is close enough to the selected approach path. The ICAO is continuing development of a specification for service levels that would support Category II and III approaches. iii. Benefits of the GLS From the user perspective, the GBAS service can offer significantly better performance than an ILS. The guidance signal has much less noise because there are no beam bends caused by reflective interference (from buildings and vehicles). However, the real value of the GLS is the promise of additional or improved capabilities that the ILS cannot provide. For example, the GLS can; provide approach and takeoff guidance service to multiple runways through a single GBAS facility, optimise runway use by reducing the size of critical protection areas for approach and takeoff operations compared with those needed for ILS, provide more flexible taxiway or hold line placement choices, simplify runway protection constraints, provide more efficient aircraft separation or spacing standards for air traffic service provision, and provide takeoff and departure guidance with a single GBAS facility. ATNS/HO/C09/30/02/01 Page 122 of July 2010

123 From the service provider perspective, the GBAS can potentially provide several significant advantages over the ILS. First, significant cost savings may be realised because a single system may be able to support all runways at an airport. Operational constraints often occur with the ILS when an Air Traffic Service provider needs to switch a commonly used ILS frequency to serve a different runway direction. This is not an issue with the GBAS because ample channels are available for assignment to each approach. In addition, because the GBAS serves all runway ends with a single VHF frequency, the limited navigation frequency spectrum is used much more efficiently. In fact, a GBAS may even be able to support a significant level of instrument approach and departure operations at other nearby airports. The placement of GBAS ground stations is considerably simpler than for the ILS because GBAS service accuracy is not degraded by any radio frequency propagation effects in the VHF band. Unlike the ILS, which requires level ground and clear areas on the runway, the siting of a GBAS VHF transmitter can be more flexible than ILS. GBAS receivers do not need to be placed near a runway in a specific geometry, as is the case with the ILS or MLS. Hence, this virtually eliminates the requirements for critical protection areas or restricted areas to protect against signal interference on runways and nearby taxiways. Finally, the GBAS should have less frequent and less costly flight inspection requirements than the ILS because the role of flight inspection for GBAS is different. Traditional flight inspection, if needed at all, primarily would apply only during the initial installation and ground station commissioning. This flight inspection would verify the suitability of the various approach path (FAS) definitions and ensure that the GBAS-torunway geometry definitions are correct. Because verifying the coverage of the VDB data link principally is a continuity of service issue rather than an accuracy or integrity issue, it typically would not require periodic inspection. GBAS systems capable of supporting Category II and III operations internationally are envisioned. Airborne system elements that would be necessary for the enhanced GLS capability (e.g., MMR and GLS automatic landing provisions) already are well on the way to certification or operational authorisation. Airborne systems and flight deck displays eventually will evolve to take full advantage of the linear characteristic of the GLS over the angular aspects of the ILS. iv. GLS Operations in the US Flight-test and operational experience with the GLS has been excellent. Many GLS-guided approaches and landings have been conducted successfully at a variety of airports and under various runway conditions. Both automatic landings and landings using head-up displays have been accomplished safely through landing rollout, in both routine and non-normal conditions. On the pilot s flight displays, the GLS has been unusually steady and smooth when compared with the current ILS systems even when critical areas necessary for the ILS approaches were unprotected during the GLS approaches. ATNS/HO/C09/30/02/01 Page 123 of July 2010

124 4 THE PERFORMANCE BASED NAVIGATION CONCEPT 4.1 Description of Performance Based Navigation Introduction The continuing growth of aviation places increased demands on airspace capacity thereby emphasising the need for optimum utilisation of available airspace. Improved operational efficiency derived from the application of area navigation (RNAV) has resulted in the development of different RNAV applications in various regions of the world and for all phases of flight. These airborne applications could potentially be expanded to provide guidance for ground movement operations. RNAV systems evolved in a manner similar to air routes and procedures based on conventional ground-based NAVAIDS. Historically a specific RNAV system would be identified and its performance would then be evaluated through a combination of analysis and flight testing. For domestic operations, the initial RNAV systems used VOR and DME as navigation signal source to calculate position, for oceanic operations various types of inertial navigation systems (INS) were employed. These new systems were each developed, evaluated and certified separately. Airspace and obstacle clearance criteria were developed based on the performance of the available equipment. In some cases, the individual model and make of equipment that could be operated within the airspace concerned was specifically identified. Such prescriptive requirements resulted in delays to the introduction of new RNAV system capabilities and higher costs for maintaining appropriate certification. To avoid such prescriptive requirements, the ICAO developed an alternative method for defining equipage requirements by specifying the performance requirements. This is termed Performance-Based Navigation (PBN). Requirements for navigation applications on specific routes or within a specific airspace must be defined and regulated in a clear and concise manner by the appropriate authority. This will enable compliance by air operators with specific airspace requirements, including navigation specifications that must be developed to allow the maximum benefit possible by the wide spread application of RNAV procedures. a. General. The PBN concept specifies that aircraft RNAV system performance requirements be defined in terms of accuracy, integrity, availability, continuity and functionality required for the proposed operations in the context of a particular airspace concept, when supported by the appropriate navigation infrastructure. The PBN concept represents a shift from sensor-based to Performance-Based Navigation. Performance requirements are identified in navigation specifications, which also identify the choice of navigation sensors and equipment that may be used to meet the performance requirements. The ICAO defined navigation specifications provide specific implementation guidance for States and operators in order to facilitate global harmonization. The PBN concept suggests that during PBN implementation the first step would be to define and then publish generic navigation requirements based on specific operational requirements. Operators then evaluate equipment options in respect of available technology and navigation infrastructure. The operator is thus free to select the most cost-effective option in terms of equipment to meet the published requirements for operation in a particular airspace. Technology can evolve over time without requiring published procedures to be revisited, provided that the required navigation performance is provided by the RNAV system (or RNP system). ATNS/HO/C09/30/02/01 Page 124 of July 2010

125 b. Benefits. PBN offers a number of advantages over the sensor-specific method of airspace and procedure design. For instance, PBN: i. reduces the need to maintain sensor-specific routes and procedures, and their associated costs. For example, moving a single VOR ground facility can impact dozens of procedures, VOR approaches, missed approaches, etc. Adding new sensor-specific procedures will compound this cost, and the rapid growth in available navigation systems would soon make sensor-specific routes and procedures unaffordable; ii. avoids the need for development of sensor-specific operations with each new evolution of navigation systems, which would be cost-prohibitive. The expansion of GNSS is expected to contribute to the continued diversity of RNAV systems in different aircraft. The original basic GNSS equipment is evolving due to the development of augmentations such as SBAS, GBAS and GRAS, while the introduction of Galileo and the modernisation of GPS and GLONASS will further improve GNSS performance. The use of GNSS/inertial integration is also expanding; iii. allows for more efficient use of airspace (route placement, fuel efficiency, noise abatement, etc.); iv. clarifies the way in which RNAV systems are used; and v. facilitates the operational approval process for operators by providing a limited set of navigation specifications intended for global use. c. Context of PBN. PBN is one of several enablers of an airspace concept. Communications, ATS surveillance and ATM are also essential elements of an airspace concept. The concept of PBN relies on the use of RNAV systems. There are two core input components for the application of PBN: i. The NAVAID infrastructure; ii. The navigation specification; Applying the above components in the context of the airspace concept to ATS routes and instrument procedures results in a third component: iii. The navigation application. d. Scope of Performance Based Navigation. i. Lateral Performance For legacy reasons associated with the previous RNP concept, PBN is currently limited to operations with linear lateral performance requirements and time constraints. For this reason, ATNS/HO/C09/30/02/01 Page 125 of July 2010

126 operations with angular lateral performance requirements (i.e. approach and landing operations with vertical guidance for APV-I and APV-II GNSS performance levels, as well as ILS/MLS/GLS precision approach and landing operations) are not yet addressed by the ICAO. Linear vs. Angular Guidance Note: While at present the PBN manual does not provide any navigation specification defining longitudinal flight technical error - FTE (i.e. required time of arrival or 4D control), the accuracy requirement of RNAV and RNP specifications are defined for the lateral and longitudinal dimensions, thereby enabling future navigation specifications defining FTE to be developed ii. Vertical Performance Unlike the lateral monitoring and obstacle clearance, for barometric VNAV operations (as discussed under All Weather Operations, Sensor Specific Area Navigation Procedures) there is neither alerting on vertical position error nor is there a two-times relationship between a 95 per cent required total system accuracy and the performance limit. Therefore, barometric VNAV is not considered as vertical RNP Navigation Specification A navigation specification is used by a State as the basis for the development of airworthiness and operational approval requirements. The navigation specification details the performance required of the RNAV system in terms of accuracy, integrity, availability and continuity, what navigation functionalities the RNAV system must have, which navigation sensors must be integrated into the RNAV system and what requirements are placed on the flight crew. The ICAO navigation specifications are contained in PBN Manual Doc 9813 Volume II. ATNS/HO/C09/30/02/01 Page 126 of July 2010

127 A navigation specification is either a RNP specification or a RNAV specification. A RNP specification includes a requirement for on-board self-contained performance monitoring and alerting, while a RNAV specification does not. a. On-board Performance Monitoring and Alerting. On-board performance monitoring and alerting is the main element that determines if the RNAV system complies with the safety level associated with a particular RNP application. This relates to both lateral and longitudinal navigation performance and it allows the aircrew to monitor the navigation performance against the required standard for the operation. RNP systems provide improvements on the integrity of operation and this may permit closer route spacing in a specific airspaces. The use of RNP systems may therefore offer significant safety, operational and efficiency benefits. On-board means that the performance monitoring and alerting is affected on board the aircraft, the monitoring and alerting relates to: Flight technical error (FTE) Navigation system error (NSE) Path definition error (PDE) which is considered negligible. ATNS/HO/C09/30/02/01 Page 127 of July 2010

128 Containment refers to the region within which the aircraft will remain 95% of the time. The associated terms have been containment value and containment distance and the related airspace protection on either side of a RNAV ATS route. Containment Limits Monitoring refers to the functional requirements of the aircraft s navigation system performance with regard to its ability to determine positioning error and or to follow the desired path. Alerting relates to the crew being informed if the aircraft s navigation system fails to perform to the required standard. RNP Monitoring and Alerting b. Navigation Functional Requirements. Navigation system functional requirements are defined to demand either a RNAV system or A RNP system. Both the RNAV system and RNP system specifications include requirements for certain navigation functionalities. At the basic level, these functional requirements are: Continuous indication of aircraft position relative to track to be displayed to the pilot flying on a navigation display, The display must be situated in the primary field of view of the pilot flying; A display of distance and bearing to the active (To) waypoint; A display of ground speed or time to the active (To) waypoint; A navigation data storage function; and An appropriate failure indication of the RNAV system, including the sensors. More sophisticated navigation specifications include the requirement for navigation databases (see section 1.2.2) and the capability to execute database procedures. ATNS/HO/C09/30/02/01 Page 128 of July 2010

129 c. Designation of RNP and RNAV Specifications. Designation of RNP and RNAV expressed by the letter X denotes the lateral navigation accuracy in nautical miles, which is expected to be achieved at least 95% of the flight time by aircraft operating in a particular airspace, or on a particular procedure or route. The navigation specification designation is the abbreviated title for the navigation system (RNAV or RNP system see note below) performance and functionality requirements. Note: Here we are referring to the RNAV system and RNP system as understood under the new PBN concept. The fundamental difference being that an RNP system shall include onboard monitoring and alerting where as an RNAV system does not include this functionality. i. RNP Specification. A navigation specification based on RNAV that includes the requirement for performance monitoring and alerting. RNP specifications are designated by the prefix RNP followed by the numerical value of the navigation accuracy for the intended operation e.g. RNP 4. ii. RNAV Specification. A navigation specification based on RNAV that does not include the requirement for performance monitoring and alerting. RNAV specifications are designated by the prefix RNAV followed by the numerical value of the navigation accuracy for the intended operation e.g. RNAV 5. Approach navigation specifications cover all segments of the instrument approach procedure from the arrival to the missed approach. The designation for approach is expressed by the prefix RNP only and is followed by an abbreviated suffix e.g. RNP APCH or RNP AR APCH. Due to the definitive nature of navigation specifications, an aircraft approved for stringent accuracy requirement e.g. a RNP specification is not automatically approved for a less stringent accuracy RNAV specification. This is due to the difference is in the functional requirements for each navigation specification and therefore aircraft approved for a more stringent accuracy requirement may not necessarily meet the functional requirements for a less stringent accuracy requirement. ATNS/HO/C09/30/02/01 Page 129 of July 2010

130 d. RNP Concept vs. RNAV. i. Oceanic, Remote Continental, En-Route and Terminal Operations For oceanic, remote continental, en-route and terminal operations, a RNP specification is designated as RNP X, e.g. RNP 4. A RNAV specification is designated as RNAV X, e.g. RNAV 1. If two navigation specifications share the same value for X, they may be distinguished by use of a prefix, e.g. Advanced-RNP 1 and Basic-RNP 1. For both RNP and RNAV designations, the expression X (where stated) refers to the lateral navigation accuracy in nautical miles, which is expected to be achieved at least 95 per cent of the flight time by the population of aircraft operating within the airspace, route or procedure. ii. Approach Approach navigation specifications cover all segments of the instrument approach. RNP specifications are designated using RNP as a prefix and an abbreviated textual suffix, e.g. RNP APCH or RNP AR APCH. There are no RNAV approach specifications. (1) PBN Procedures (2) Basic-RNP 1 (3) Advanced - RNP 1 (Future development) (4) RNP 2 (Future development) (5) RNP APCH (6) RNP AR APCH iii. Understanding RNAV and RNP Designations In cases where navigation accuracy is used as part of the designation of a navigation specification, it should be noted that navigation accuracy is only one of the many performance requirements included in a navigation specification. Because specific performance requirements are defined for each navigation specification, an aircraft approved for RNP specifications is not automatically approved for all RNAV specifications. Similarly, an aircraft approved for RNP or RNAV specification having a stringent accuracy requirement (e.g. RNP 0.3 specification) is not automatically approved for a navigation specification having a less stringent accuracy requirement (e.g. RNP 4). It may seem logical, for example, that an aircraft approved for Basic-RNP 1 be automatically approved for RNP 4, however, this is not the case. Aircraft approved to the more stringent accuracy requirements may not necessarily meet some of the functional requirements of the navigation specification having a less stringent accuracy requirement. iv. Flight Planning of RNAV and RNP Designations Manual or automated notification of an aircraft s qualification to operate along an ATS route, on a procedure or in a particular portion of airspace is provided to ATC via the Flight Plan. Flight Plan procedures are addressed in Procedures for Air Navigation Services Air Traffic Management (PANS-ATM) (Doc 4444). ATNS/HO/C09/30/02/01 Page 130 of July 2010

131 v. Accommodating Inconsistent RNP Designations The existing RNP 10 designation is inconsistent with PBN RNP and RNAV specifications. RNP 10 does not include requirements for on-board performance monitoring and alerting. For purposes of consistency with the PBN concept, RNP 10 is referred to as RNAV 10 in this manual. Renaming current RNP 10 routes, operational approvals, etc., to a RNAV 10 designation would be an extensive and expensive task, which is not cost-effective. Consequently, any existing or new operational approvals will continue to be designated RNP 10, and any charting annotations will be depicted as RNP 10 (see graphic below). Accommodating existing and future designations In the past, the United States and member States of the European Civil Aviation Conference (ECAC) used regional RNAV specifications with different designators. The ECAC applications (P-RNAV and B-RNAV) will continue to be used only within those States. Over time, ECAC RNAV applications will migrate towards the international navigation specifications of RNAV 1 and RNAV 5. The United States migrated from the US RNAV Types A and B to the RNAV 1 specification in March vi. Minimum Navigation Performance Specification (MNPS) Aircraft operating in the North Atlantic airspace are required to meet a minimum navigation performance specification (MNPS). The MNPS has intentionally been excluded from the above designation scheme because of its mandatory nature and because future MNPS implementations are not envisaged. The requirements for MNPS are set out in the Consolidated Guidance and Information Material concerning Air Navigation in the North Atlantic Region (NAT Doc 001). vii. Future RNP Designations It is possible that RNP specifications for future airspace concepts may require additional functionality without changing the navigation accuracy requirement. Examples of such future navigation specifications may include requirements for vertical RNP and time-based (4D) capabilities. The designation of such specifications will need to be addressed in future developments of the ICAO PBN manual. ATNS/HO/C09/30/02/01 Page 131 of July 2010

132 4.1.3 NAVAID Infrastructure NAVAID Infrastructure comprises the NAVAIDs that support or provide the position capabilities and is referred to as ground- or space-based NAVAIDS. NAVAIDS are categorised as follows: Ground-based NAVAIDs include DME and VOR, or Space-based NAVAIDs include GNSS elements Navigation Application This is the application of a navigation specification and associated NAVAID infrastructure to ATS routes, instrument approach procedures and/or defined airspace volume in accordance with the airspace concept, i.e. the concept of matching the navigation specification against the navigation aid infrastructure. Navigation application includes RNAV or RNP SIDs and STARs, RNAV or RNP ATS routes and RNP approach procedures. The designator of a Navigation Application matches the corresponding Navigation Specification, i.e. A RNP application is supported by RNP specifications, and A RNAV application is supported by RNAV specifications. Navigation Applications indicating the designation of the required Navigation Specification plus any established limitation imposed for the particular Navigation Application will be outlined on the relevant instrument procedure charts and AIPs. Application of navigation specification by flight phase: Flight Phase Navigation Specification En-route Oceanic/remote En-route Continental Arrival Approach Initial Intermediate Final Missed Departure RNAV RNAV RNAV RNAV b 1 RNP4 4 Basic-RNP1 1a,c 1a 1a 1a,b 1a,c RNPAPCH a. The navigation application is limited to use on STARs and SIDs only. b. The area of application can only be used after the initial climb of a missed approach phase. c. Beyond 30 NM from the airport reference point (ARP), the accuracy value for alerting becomes 2 NM. ATNS/HO/C09/30/02/01 Page 132 of July 2010

133 4.1.5 Future Developments Under PBN, Navigation Applications will progress from 2D to 3D/4D. Consequently, on-board performance monitoring and alerting is still to be developed in the vertical plane (vertical RNP) and ongoing work is aimed at harmonising longitudinal and linear performance requirements. It is also possible that angular performance requirements associated with approach and landing may be included in the scope of PBN in the future. Similarly, specifications to support helicopter-specific navigation applications and holding functional requirements may also be included. Operators are preparing for the application of trajectory-based operations (TBO), i.e. 3D and 4D RNAV operations. TBO presents lateral and vertical flight profile for aircraft that are specific, but highly flexible and adaptable to operational needs. These types of operations allow for real time flight profile changes depending on the navigation accuracy required. This type of operation also allows for the definition of climb and descent points as well as time of arrival definition to meet the prevailing ATS requirement. The availability of this level of navigation capability from takeoff to landing will ensure navigation accuracy along a route, procedure or airspace both laterally and vertically. As more reliance is placed on GNSS, the development of airspace concepts will increasingly need to ensure the coherent integration of navigation, communication and ATS surveillance enablers. Future ATM developments will allow different States to employ the most cost effective and relevant navigation specifications. See the following example; An example of different States employing different NAVAID solutions to achieve a similar result. The RNAV 1 specification in Volume II of this manual shows that any of the following navigation sensors can meet its performance requirements: GNSS or DME/DME/IRU or DME/DME. Sensors needed to satisfy the performance requirements for a RNAV 1 specification in a particular State are not only dependent on the aircraft on-board capability. A limited DME infrastructure or GNSS policy considerations may lead the authorities to impose specific navigation sensor requirements for a RNAV 1 specification in that State. As such, State A s AIP could stipulate GNSS as a requirement for its RNAV 1 specification because State A only has GNSS available in its navaid infrastructure. State B s AIP could require DME/DME/IRU for its RNAV 1 specification (policy decision to not allow GNSS). Each of these navigation specifications would be implemented as a RNAV 1 application. However, aircraft equipped only with GNSS and approved for the RNAV 1 specification in State A would not be approved to operate in State B. ATNS/HO/C09/30/02/01 Page 133 of July 2010

134 a. Merge Point Procedure. A Merge Point Procedure is a published instrument procedure that is designed to make full use of the capability of the airborne navigation systems available today. This is achieved by requiring and aircraft to follow a published route to final approach, whilst complying with height/level, speed and time restrictions and with minimal or no ATC intervention (i.e. no vectoring and minimal talking). This type of procedure is in use today at a number of the major European airports, Paris, Frankfurt and Brussels to name a few. Let s see how this is possible and we will start by defining a few terms. i. Point Merge System A Point Merge system forms part of a route structure, enabling the integration of two or more inbound flows into one sequence and is characterised by the features described below. ii. Merge point Traffic integration at a merge point is achieved by merging inbound flows to a single point. After this merge point, aircraft are established on a fixed common route until the exit of the Point Merge system. iii. Sequencing legs Before the merge point, a sequencing leg is dedicated to path stretching/shortening for each inbound flow. While along a sequencing leg, aircraft can be instructed to fly Direct To the merge point at any appropriate time (i.e. be kept for a certain amount of time on the leg for path stretching, or inversely sent early direct to the merge point for path shortening). Sequencing legs have a pre-defined maximum length at iso-distance from the merge point ATNS/HO/C09/30/02/01 Page 134 of July 2010

135 Merge Point Figure 1 In order for the controller to easily and intuitively determine the appropriate moment to issue the Direct-To instructions for each aircraft, based on its spacing with the preceding aircraft in the sequence, and without requiring the support of any new ground tool, the geometry of the Point Merge System shall ensure that: aircraft left flying on a sequencing leg are kept (approximately) at the same distance ( iso-distance ) from the merge point all along this leg (this requirement has an impact on the shape of the sequencing legs, which shall be as close as possible to arcs of circle), and distinct sequencing legs are (approximately) located at the same distance from the merge point. (1) Example Shown here is a typical Point Merge System depicting a simple configuration with two inbound flows. This Point Merge System is composed of two sequencing legs that are: parallel, flown in opposite directions and are vertically separated; segmented, forming quasi-arcs centred on the merge point (iso-distance requirement). Notes: The resulting envelope of possible paths towards the merge point forms a triangleshaped area. (1) Aircraft enter the Point Merge System upon reaching a defined waypoint which will generally be located ahead of the sequencing leg s entry. (2) Aircraft leave the Point Merge System upon reaching a defined waypoint which will generally be located after the merge point. ATNS/HO/C09/30/02/01 Page 135 of July 2010

136 At this stage, it shall be remarked that the Point Merge procedure is not thought of as an open-ended STAR. It should be designed so that if the aircraft reaches the end of the sequencing leg without receiving a Direct To clearance (which is not expected to occur under nominal circumstances), it turns automatically towards the merge point as shown in the diagram adjacent. In the rest of the document, we will always consider the Point Merge procedure as being (part of) a closed STAR. However, for the sake of readability, the figures in this document will generally not include the closing part of the Point Merge procedure. iv. Variants There is actually a wide range of possible variants regarding the geometry and parameters of a Point Merge System. Still, all these possible options are based on the same high level principles, and are compatible with the proposed operating method. Local constraints may impose specific design choices, conversely, some environments may offer certain flexibility in the design of a route structure supporting Point Merge operations. In particular, the length of the sequencing legs will directly influence the maximum extent of path stretching. One may develop any one of a number of permutations varying from the basic Point Merge System through to a Point Merge System with fully dissociated sequencing legs. Shown adjacent is an example of a Point Merge Systems dealing with two inbound flows and comprising two sequencing legs that are: shorter, separate (dissociated) and of opposite directions (left hand side diagram) or same direction (right hand side diagram); segmented, approximating arcs of a circle centred on the merge point (iso-distance requirement). Merge Point Figure 3 Merge Point Figure 2 v. Impact on vertical profiles In the Merge Point Figure 1 above (parallel sequencing legs), aircraft from the outer sequencing leg will generally cross the inner leg once instructed Direct To the merge point, lateral separation between aircraft from different arrival flows is not ensured by design. Consequently, the legs will need to be vertically separated (see Merge Point Figure 4 as an example). Different solutions may be envisaged ATNS/HO/C09/30/02/01 Page 136 of July 2010

137 one option may be to require aircraft to level off when flying along the sequencing legs. This would be the most constraining option. However, even in that case, when leaving the legs, the distance to go (DTG) will be known by the FMS and in case the Point Merge System is located in such a way that aircraft entering it have already reached their top of descent (TOD), continuous descent approaches (CDAs) will already be possible from the level/altitude of the sequencing legs; a second option would be to define and publish vertical restrictions that would enable aircraft to follow a gentle descent along both legs (e.g. from FL130 down to FL110 on one leg, and from FL100 to FL080 on the other one see Merge Point Figure 5). Once instructed to fly Direct To the merge point, the vertical profile can be adjusted taking into account the updated DTG information. This will then allow for the application of the CDA concept from earlier on in the descent or even allow for CDA from the cruise level. In the Merge Point Figure 3 above (dissociated sequencing legs), aircraft flying the procedure are normally expected to be separated longitudinally and/or laterally from each other. Consequently, the vertical separation constraint is released (subject to other local requirements) and aircraft could be in descent at all times while in the Point Merge System. More efficient CDAs from closer to the cruise level may become possible. vi. Separation between sequencing legs As a general rule, the design of the route structure shall enable segregation between arrivals from different flows (in addition to strategic de-confliction between arrivals and departures), before the sequence is built. In particular, sequencing legs shall be appropriately separated in the lateral and/or vertical planes. In case of parallel sequencing legs, due consideration shall be given to the following aspects regarding their lateral separation: they shall not be located too far apart in the horizontal plane, so as to comply with the requirement to be approximately at the same distance from the merge point, and thus gain some precision on inter-aircraft spacing when applying the procedure. From this perspective, it is recommended to avoid using a large lateral distance between parallel legs (e.g. equal to, or larger than the required separation); on the other hand, the legs should not be designed too close to each other in order to avoid display cluttering on the controller s radar display. Therefore a trade-off has to be found, e.g. sequencing legs 2nm apart (which, assuming a 3nm separation standard for instance, also requires the sequencing legs to be vertically separated as stated above). Regarding vertical separation between the sequencing legs, due consideration shall be given to the following aspects: differences in levels/altitudes used along the sequencing legs shall not be too large; this is due to the need to keep aircraft at compatible speeds for sequence building/maintenance, and in view of their descent for reaching the same altitude at the merge point while ensuring longitudinal separation; parallel sequencing legs shall on the other hand be vertically separated e.g. each assigned with a different published level/altitude (i.e. at least 1000ft apart), or using ATNS/HO/C09/30/02/01 Page 137 of July 2010

138 appropriate vertical restrictions; consequently, again, in that case a trade-off has to be found. vii. Altitude restrictions In order to ensure that there is no inadvertent descent while aircraft are flying along the sequencing leg, the minimum altitude for the leg should be published as an at or above altitude restriction (or an altitude window) at its last waypoint (see Merge Point Figure 4 below). It is further recommended that an appropriate altitude restriction in the form of at or above or vertical window is defined at the exit of the Point Merge System and/or at its merge point. This will help to influence the vertical profile calculations once the aircraft has been cleared for the procedure. In case it is considered necessary to keep the aircraft at a specific level/altitude when flying along the sequencing legs (e.g. parallel legs with levelling-off), then at altitude restrictions should be defined for the start and end point of these legs. Furthermore, if the parallel legs are of opposite direction (as shown in Merge Point Figure 4), these published vertical restrictions will probably be required in order to minimise ACAS alerts. In case of parallel sequencing legs, in order to mitigate the risk of an aircraft still being in descent whilst entering the sequencing leg (and therefore allow some time for ATCO to detect a potential level bust), it is recommended that the level restriction be published on a point ahead of the sequencing leg, ensuring that the aircraft levels off prior to entry (as shown in Merge Point Figure 4). Note: A similar design precautions are also required in order to minimise ACAS alerts due to the close location of legs start and end points in case of opposite parallel sequencing legs. Merge Point Figure 5 Merge Point Figure 4 Merge Point Figure 5 provide examples of published altitude restrictions for a Point Merge System in Approach airspace, in case of close parallel sequencing legs with level-offs, parallel legs with gentle descent, or dissociated sequencing legs. In this example, the aircraft are required to level off along the ATNS/HO/C09/30/02/01 Page 138 of July 2010

139 Merge Point Figure 7 Merge Point Figure 6 parallel sequencing legs so as to ensure vertical separation. At vertical restrictions are published at the start and end points of the legs. In Merge Point Figure 6, vertical restrictions are set on the parallel legs so that aircraft from IAF1 will remain below aircraft from IAF2 while along the legs. In both cases however, they may follow a gentle descent. Such design may provide a seamless transition between: situations where traffic load still enables to follow an efficient vertical path (aircraft do not fly a long distance along the sequencing legs and do not need to level off), and situations where the traffic load is such that the need to achieve a safe and efficient runway sequence does not allow anymore the systematic optimisation of individual vertical profiles (aircraft fly longer distances along the legs and reach a point where they may need to level off). In Merge Point Figure 7, legs are dissociated and aircraft from IAF1 and from IAF2 may follow independently optimised vertical profiles. There is an uncertainty on the distance to go until aircraft turn Direct To the merge point, at which time the aircrew can adjust the rate of descent according to the actual remaining distance to touchdown. Vertical restrictions may be published as pictured here at the first point of each leg so as to ensure that aircraft turning immediately to the merge point will be able to descend with a shorter DTG. viii. Speed restrictions Speed restrictions may also be defined at certain waypoints in a Point Merge system. For instance, if it is the intention of ATC to reduce all aircraft to a common speed when they enter the sequencing leg, this should be published as a speed restriction at the entry waypoint. It may then be desirable to also publish an altitude restriction at the same waypoint to ensure that all P-RNAV systems take account of the speed restriction. ATNS/HO/C09/30/02/01 Page 139 of July 2010

140 ix. Other charting aspects Waypoints in a Point Merge System (including the merging point) should be fly-by waypoints, with the exception of the last point at the end of the sequencing leg in the closing part of the procedure which should be a fly-over waypoint. The waypoint names in a Point Merge System shall conform to naming conventions such as those published for RNAV waypoints. Waypoints on the sequencing legs could be identified using the alphanumeric naming conventions. The merge point should be considered as a strategic waypoint to ATC, and thus be named using 5 letter globally unique pronounceable ICAO Name codes. The Point Merge procedure should be detailed in the AIP, or in a supporting AIC. The charts should not be cluttered with detailed notes about the concept apart from a note stating Point Merge procedures in operation, expect clearance direct to merge points (WPT NAMES) once past IAF. CDA profiles to be followed once inbound to the merge point, or a similar statement. ATNS/HO/C09/30/02/01 Page 140 of July 2010

141 4.2 Airspace Concept Introduction An airspace concept may be viewed as a general vision or a master plan for a particular airspace. Based on particular principles, an airspace concept is geared towards specific objectives. Airspace concepts need to include a certain level of detail if changes are to be introduced within a particular portion of airspace. Details could explain, for example, airspace organization and management and the roles to be played by various stakeholders and airspace users. Airspace concepts may also describe the different roles and responsibilities, mechanisms used and the relationships between people and machines. Strategic objectives drive the general vision of the airspace concept. These objectives are usually identified by airspace users, air traffic management (ATM), airports as well as environmental and government policy. It is the function of the airspace concept and the concept of operations to respond to these requirements. The strategic objectives which most commonly drive airspace concepts are safety, capacity, efficiency, access and the environment. As Examples 1 and 2 below suggest, strategic objectives can result in changes being introduced to the airspace concept. Example 1 Safety: The design of RNP instrument approach procedures could be a way of increasing safety (by reducing Controlled Flights into Terrain (CFIT). Capacity: Planning the addition of an extra runway at an airport to increase capacity will trigger a change to the airspace concept (new approaches to SIDs and STAR required). Efficiency: A user requirement to optimise flight profiles on departure and arrival could make flights more efficient in terms of fuel burn. Environment: Requirements for reduced emissions, noise preferential routes or continuous descent arrivals/approaches (CDA), are environmental motivators for change. Access: A requirement to provide an approach with lower minima than supported by conventional procedures, to ensure continued access to the airport during bad weather, may result in the development and publication of a RNP approach to that runway. ATNS/HO/C09/30/02/01 Page 141 of July 2010

142 Example 2 Although GNSS is associated primarily with navigation, GNSS is also the backbone of ADS-B surveillance applications. As such, GNSS positioning and track-keeping functions are no longer confined to being a navigation enabler to an airspace concept. GNSS, in this case, is also an ATS surveillance enabler. The same is true of data-link communications: data are used by an ATS surveillance system (for example, in ADS-B and navigation) The Airspace Concept a. Airspace Concepts and Navigation Applications. The cascade effect from strategic objectives to the airspace concept places requirements on the various enablers such as communication, navigation, ATS surveillance, air traffic management and flight operations. The navigation functional requirements within a Performance-Based Navigation context need to be identified. These navigation functionalities are formalised in a navigation specification which, together with a navigation aid infrastructure, supports a particular navigation application. As part of an airspace concept, navigation applications also have a relationship to communication, ATS surveillance, ATM, ATC tools and flight operations, which are also inherent in the airspace concept. Relationship: Performance-Based Navigation and Airspace Concept ATNS/HO/C09/30/02/01 Page 142 of July 2010

143 4.2.3 Airspace Concepts by Area of Operation Area of operation a. Oceanic and Remote Continental. Oceanic and remote continental airspace concepts are currently served by two navigation applications, RNAV 10 and RNP 4. Both these navigation applications rely primarily on GNSS to support the navigation element of the airspace concept. In the case of the RNAV 10 application, no form of ATS surveillance service is required. In the case of the RNP 4 application, ADS contract (ADS-C) is used. Note: RNAV10 retains the RNP10 designation. AREA of OPERATION NAVIGATION APPLICATION NAVIGATION SPECIFICATION NAVAID INFRASTRUCTURE COMMUNICATION SURVEILLANCE Oceanic En route ATS routes RNAV 10 GNSS RTF (voice) Procedural Service Oceanic En route ATS routes RNP 4 GNSS RTF (voice) RTF and Data links(cpdlc & ADS-C) Oceanic En route ATS routes RNAV10 IRS RTF (voice) RTF and Data links(cpdlc & ADS-C) Procedural Service Procedural Service Remote Continental En route ATS routes RNAV 10 GNSS RTF (voice) Procedural Service Remote Continental Remote Continental En route ATS routes RNP 4 GNSS RTF (voice) RTF and Data links(cpdlc & ADS-C) En route ATS routes RNAV10 IRS RTF (voice) RTF and Data links(cpdlc & ADS-C) Procedural Service Procedural Service ATNS/HO/C09/30/02/01 Page 143 of July 2010

144 b. Continental En-Route. Continental en-route airspace concepts are currently supported by RNAV applications. RNAV 5 is used in the Middle East (MID) and European (EUR) Regions. It is designated as B-RNAV (Basic RNAV in Europe and RNP 5 in the Middle East. In the United States, a RNAV 2 application supports an en-route continental airspace concept. At present, continental RNAV applications support airspace concepts which include radar surveillance and direct controller pilot communication (voice). AREA of OPERATION NAVIGATION APPLICATION NAVIGATION SPECIFICATION NAVAID INFRASTRUCTURE COMMUNICATION SURVEILLANCE Continental En-route En route ATS routes RNAV 5 GNSS DME/DME VOR/DME RTF (voice) ATS Surveillance Service Continental En-route En route ATS routes RNP 1 GNSS DME/DME RTF (voice) Procedural Service Continental En-route En route ATS routes RNAV 2 no IRS RNAV 1 with IRS RNAV 1 no IRS but adequate DME GNSS DME/DME RTF (voice) Procedural Service Continental En-route En route ATS routes None available GNSS DME/DME RTF (voice) Procedural Service c. Terminal Airspace: Arrival and Departure. Existing terminal airspace concepts, which include arrival and departure, are supported by RNAV applications. These are currently used in the European (EUR) Region and the United States. The European terminal airspace RNAV application is known as Precision RNAV (P-RNAV). As indicate in the PBN Manual Doc Volume II, although the RNAV 1 specification shares a common navigation accuracy with P-RNAV, this regional navigation specification does not satisfy the full requirements of the RNAV 1 specification shown in Volume II. As of the publication of this manual, the United States terminal airspace application formerly known as US RNAV Type B has been aligned with the PBN concept and is now called RNAV 1. Basic-RNP 1 has been developed primarily for application in non-radar, low-density terminal airspace. In future, more RNP applications are expected to be developed for both en-route and terminal airspace. AREA of OPERATION Terminal Terminal Terminal NAVIGATION APPLICATION SIDs and STARS SIDs and STARS SIDs and STARS NAVIGATION SPECIFICATION RNAV 2 no IRS RNAV 1 with IRS RNAV 1 no IRS but adequate DME NAVAID INFRASTRUCTURE GNSS DME/DME COMMUNICATION RTF (voice) SURVEILLANCE ATS Surveillance Service Basic - RNP 1 GNSS RTF (voice) Procedural Service Basic - RNP 1 RNAV 1 with GNSS only GNSS DME/DME RTF (voice) ATS Surveillance Service ATNS/HO/C09/30/02/01 Page 144 of July 2010

145 d. Approach. Approach concepts cover all segments of the instrument approach, i.e. initial, intermediate, final and missed approach. They will increasingly call for RNP specifications requiring a navigation accuracy of 0.3 NM to 0.1 NM or lower. Typically, three sorts of RNP applications are characteristic of this phase of flight: new procedures to runways never served by an instrument procedure, procedures either replacing or serving as backup to existing instrument procedures based on different technologies, and procedures developed to enhance airport access in demanding environments. The relevant RNP specifications covered in the PBN Manual Doc Volume II are RNP APCH and RNP AR APCH. AREA of OPERATION NAVIGATION APPLICATION NAVIGATION SPECIFICATION NAVAID INFRASTRUCTURE COMMUNICATION SURVEILLANCE Approach Approach RNP APCH GNSS RTF (voice) ATS Surveillance Service Approach Approach RNP APCH GNSS RTF (voice) Procedural* Service Approach Approach RNP AR APCH GNSS RTF (voice) Procedural ** Service Approach Approach RNP AR APCH GNSS RTF (voice) ATS ** Surveillance Service ATNS/HO/C09/30/02/01 Page 145 of July 2010

146 4.3 Stakeholder Uses of Performance Based Navigation Introduction Various stakeholders are involved in the development of the airspace concept and the resulting navigation applications. These stakeholders are; airspace planners, procedure designers, aircraft manufacturers, pilots and air traffic controllers. Each stakeholder has a different role and set of responsibilities. Stakeholder involvement in PBN concept implementation is at; Strategic Level: Airspace planners and procedure designers translate the PBN concept into reality of route spacing, aircraft separation minima and procedure design. Strategic Level: Airworthiness and regulatory authorities ensure that aircraft and crew meet the operating requirements of the intended implementation. Tactical Level: Controllers and pilot using PBN concept in real-time operations Each stakeholder will focus on a particular section of the PBN concept that is in line with their line of operation. PBN elements and specific points of interest of various stakeholders ATNS/HO/C09/30/02/01 Page 146 of July 2010

147 4.3.2 Airspace Planning The two major elements of airspace planning are determination of separation minima to be applied and route spacing for use by aircraft. The Manual on Airspace Planning Methodology for the Determination of separation Minima (Doc 9689) is a key reference document planners should consult. Separation minima and route spacing can generally be described as being a function of three factors: Navigation performance based on the PBN concept. Aircraft s exposure to risk i.e. the route configuration, traffic density and operational error. The mitigation measures which are available to reduce risk i.e. communication, surveillance which also include ATC procedures and other necessary tools. Generic model used to determine separation and ATS route spacing Aircraft-to-aircraft separation and ATS route spacing are not exactly the same. As such, the degree of complexity of the equation depicted graphically in the figures above depends on whether separation between two aircraft or route spacing criteria is being determined. Aircraft-to-aircraft separation, for example, is usually applied between two aircraft and as a consequence, the traffic density part of the risk is usually considered to be a single aircraft pair. For route spacing purposes, this is not the case: the traffic density is determined by the volume of air traffic operating along the spaced ATS routes. This means that if aircraft in a particular portion of airspace are all capable of the same navigation performance, one could expect the separation minima between a single aircraft pair to be less than the spacing required for parallel ATS routes. The complexity of determining route spacing and separation minima is affected by the availability of an ATS surveillance service and the type of communication used. If an ATS surveillance service is available, this means that the risk can be mitigated by including requirements for ATC intervention. ATNS/HO/C09/30/02/01 Page 147 of July 2010

148 a. Impact of PBN on airspace planning. When separation minima and route spacing are determined using a conventional sensorbased approach, the navigation performance data used to determine the separation minima or route spacing depend on the accuracy of the raw data from specific navigation aids such as VOR, DME or NDB. In contrast, PBN requires a RNAV system that integrates raw navigation data to provide a positioning and navigation solution. In determining separation minima and route spacing in a PBN context, this integrated navigation performance output is used. It needs to be remembered that the navigation performance required from the RNAV system is part of the navigation specification. To determine separation minima and route spacing, airspace planners fully exploit that part of the navigation specification which prescribes the performance required from the RNAV system. Airspace planners also make use of the required performance, namely, accuracy, integrity, availability and continuity to determine route spacing and separation minima. RNAV specifications and RNP specifications are applied in this process. It is expected, for example, that the separation minima and route spacing derived from a RNP 1 specification will be smaller than those derived from a RNAV 1 specification, though the extent of this improvement has yet to be assessed. In procedurally controlled airspace, separation minima and route spacing based on RNP specifications are expected to provide a greater benefit than those based on RNAV specifications. This is because the on-board performance monitoring and alerting function could alleviate the absence of ATS surveillance service by providing an alternative means of risk mitigation Instrument Flight Procedure Design Instrument flight procedure design includes the construction of routes, which include arrivals, departures and approach procedures. These procedures consist of a series of predetermined manoeuvres to be conducted solely by reference to flight instruments with specified protection from obstacles. States are responsible for ensuring that all published instrument flight procedures in their airspace can be flown safely by the relevant aircraft. Safety is not only accomplished by application of the technical criteria in the PANS-OPS (Doc 8168) and associated provisions, but also requires measures that control the quality of the process used to apply that criteria, which may include; regulation, air traffic monitoring, ground validation and flight validation. These measures must ensure the quality and safety of the procedure design product through review, verification, coordination, and validation at appropriate points in the process, so that corrections can be made at the earliest opportunity in the process. The following paragraphs regarding instrument flight procedure design describe conventional procedure design and sensor-dependent RNAV procedure design, their disadvantages and the issues that led up to PBN. ATNS/HO/C09/30/02/01 Page 148 of July 2010

149 a. Non-RNAV conventional instrument flight procedure design. Conventional procedure design is applicable to non-rnav applications when aircraft are navigating based on direct signals from ground-based radio navigation aids. The disadvantage to this type of navigation is that the routes are dependent on the location of the navigation beacons (see diagram below). This often results in longer routes since optimal arrival and departure routes are impracticable due to siting and cost constraints on installing ground-based radio navigation aids. Additionally, obstacle protection areas are comparatively large and the navigation system error increases as a function of the aircraft s distance from the navigation aid. Conventional instrument flight procedure design b. RNAV Procedures design. Initially, RNAV was introduced using sensor-specific design criteria. A fundamental breakthrough with RNAV was the creation of fixes defined by name, latitude and longitude. RNAV fixes allowed the design of routes to be less dependent on the location of NAVAIDS, therefore, the designs could better accommodate airspace planning requirements (see graphic on the next page). The flexibility in route design varied by the specific radio navigation system involved, such as DME/VOR or GNSS. Additional benefits included the ability to store the routes in a navigation database, reducing pilot workload and resulting in more consistent flying of the nominal track as compared to cases where the non-rnav procedure design was based on heading, timing or DME arcs. As RNAV navigation is accomplished using an aircraft navigation computer using data from a navigation database, a major change for the designer is the increased need for quality assurance in the procedure design process. RNAV had a number of issues and characteristics that needed to be considered. Among these were the sometimes wide variations in flight performance and flight paths of aircraft, as well as the inability to predict the behaviour of navigation computers in all situations. This resulted in large obstacle assessment areas, and, as a consequence, not much benefit was achieved in terms of reducing the obstacle protection area. ATNS/HO/C09/30/02/01 Page 149 of July 2010

150 RNAV procedure design As experience in RNAV operations grew, other important differences and characteristics were discovered. Aircraft RNAV equipment, functionalities and system configurations ranged from the simple to the complex. There was no guidance for the designer as to what criteria to apply for the aircraft fleet for which the instrument flight procedures are being designed. Some of the system behaviour was the result of the development of RNAV systems that would fly database procedures derived from ATC instructions. This attempt to mimic ATC instructions resulted in many ways to describe and define an aircraft flight path, resulting in an observed variety of flight performance. Furthermore, the progress in aircraft and navigation technology caused an array of types of procedures, each of which require different equipment, imposing unnecessary costs on the air operators. c. RNP Procedures design. RNP procedures were introduced in the PANS-OPS (Doc 8168), which became applicable in These RNP procedures were the predecessor of the current PBN concept, whereby the performance for operation on the route is defined, in lieu of simply identifying a required radio navigation system. However, due to the insufficient description of the navigation performance and operational requirements, there was little perceived difference between RNAV and RNP. In addition, the inclusion of conventional flight elements such as flyover procedures, variability in flight paths and added airspace buffer, resulted in no significant advantages being achieved in designs. As a result, there was a lack of benefits to the user-community and little or no implementation. ATNS/HO/C09/30/02/01 Page 150 of July 2010

151 d. PBN Procedures design. Area navigation using PBN is a performance-based operation in which the navigation performance characteristics of the aircraft are well specified and the problems described above for the original RNAV and RNP criteria can be resolved. The performance-based descriptions address various aircraft characteristics that were causing variations in flight trajectories, leading to more repeatable, reliable and predictable flight tracking, as well as smaller obstacle assessment areas. Examples of RNP APPROACH (RNP APCH) and RNP AUTHORISATION REQUIRED APPROACH (RNP AR APCH) are shown in the figures below. Examples of RNP APCH (left) and RNP AR APCH (right) procedures design Note: The fundamental advantage of the RNP AR APCH over the RNP APCH is the fact that AR procedures may be designed to allow operations closer to obstructions (most often high ground) and thus increase access to obstacle rich aerodrome environments. The main change for the designers will be that they will not be designing for a specific sensor but according to a navigation specification (e.g. RNAV 1). The selection of the appropriate navigation specification is based on the airspace requirements, the available NAVAID infrastructure, and the equipage and operational capability of aircraft expected to use the route. For example, where an airspace requirement is for RNAV-1 or RNAV-2, the available navigation infrastructure would have to be basic GNSS or DME/DME, and aircraft would be required to utilise either to conduct operations. Volume II of the ICAO PBN Manual (ICAO Doc 9613) provides a more explicit and complete navigation specification for the aircraft and operator as compared to PANS-OPS (Doc 8168), Volume I. The procedure design along with qualified aircraft and operators result in greater reliability, repeatability and predictability of the aircraft flight path. It should be understood that no matter what infrastructure is provided, the designer may still apply the same general design rules in fix and path placement; however, adjustments may be required based upon the associated obstacle clearance or separation criteria. Integration of the aircraft and operational criteria will enable procedure design criteria to be updated. A first effort to create such criteria is for the RNP AR APCH navigation specification. In this case, the design criteria take full account of the aircraft capabilities and are fully integrated with the aircraft approval and qualification requirements. The tightly integrated relationship between aircraft, operational and procedure design criteria for RNP AR APCH requires closer examination of aircraft qualification and operator approval, since special authorisation is required. This additional requirement will incur cost to the airlines and will make these types of procedures only cost beneficial in cases where other procedure design criteria and solutions will not fit. ATNS/HO/C09/30/02/01 Page 151 of July 2010

152 4.3.4 Airworthiness and Operational Approval Aircraft should be equipped with a RNAV system able to support the desired navigation application. The RNAV system and aircraft operations must be compliant with regulatory material (still to developed and published for South Africa) that reflects the navigation specification (not yet defined for South Africa) developed for a particular navigation application as stated in PBN Manual Doc Volume II and approved by the appropriate regulatory authority for the operation. The navigation specification details the flight crew and aircraft requirements needed to support the navigation application. This specification includes the level of navigation performance, functional capabilities, and operational considerations required for the RNAV system. The RNAV system installation should be certified in accordance with the ICAO Annex 8 Airworthiness of Aircraft and operational procedures should respect the applicable aircraft flight manual limitations, if any. The RNAV system should be operated in accordance with recommended practices described in the ICAO Annex 6 Operation of Aircraft and PANS-OPS (Doc 8168), Volume I. Flight crew and/or operators should adhere to operational limitations required for the navigation application. All assumptions related to the navigation application are listed in the navigation specification. Review of these assumptions is necessary when proceeding to the airworthiness and operational approval process. Operators and flight crew are responsible for checking that the installed RNAV system is operated in areas where the airspace concept and the NAVAID infrastructure described in the navigation specification is fulfilled. To ease this process, certification and/or operational documentation should clearly identify compliance with the related navigation specification. a. Airworthiness approval process. The airworthiness approval process assures that each item of the RNAV equipment installed is of a type and design appropriate to its intended function and that the installation functions properly under foreseeable operating conditions. Additionally, the airworthiness approval process identifies any installation limitations that need to be considered for operational approval. Such limitations and other information relevant to the approval of the RNAV system installation are documented in the Aircraft Flight Manual (AFM), or AFM Supplement, as applicable. Information may also be repeated and expanded upon in other documents such as Pilot Operating Handbooks (POH) or flight crew operating manuals. The airworthiness approval process is well established among States of the Operators and this process refers to the intended function of the navigation specification to be applied. i. Approval of RNAV systems for RNAV-X operations The RNAV system installed should be compliant with a set of basic performance requirements as described in the navigation specification, which defines accuracy, integrity and continuity criteria. It should also be compliant with a set of specific functional requirements, have a navigation database, and support each specific path terminator as required by the navigation specification. Note: For certain navigation applications, a navigation database may be optional. ATNS/HO/C09/30/02/01 Page 152 of July 2010

153 For a multi-sensor RNAV system, an assessment should be conducted to establish which sensors are compliant with the performance requirement described in the navigation specification. The navigation specification generally indicates if a single or a dual installation is necessary to fulfil availability and/or continuity requirements. The airspace concept and NAVAID infrastructure are key elements in deciding if a single or a dual installation is necessary. ii. Approval of RNP systems for RNP-X operations The RNP system installed should be compliant with a set of basic RNP performance requirements, as described in the navigation specification, which should include an on-board performance monitoring and alerting function. It should also be compliant with a set of specific functional requirements, have a navigation database, and should support each specific path terminator as required by the navigation specification. For a multi-sensor RNP system, an assessment should be conducted to establish sensors which are compliant with the RNP performance requirement described in the RNP specification. b. Operational approval. The aircraft must be equipped with a RNAV system enabling the flight crew to navigate in accordance with operational criteria as defined in the navigation specification. The State of the Operator is the authority responsible for approving flight operations. The authority must be satisfied that operational programmes are adequate. Training programmes and operations manuals should be evaluated. i. General RNAV approval process The operational approval process first assumes that the corresponding installation/airworthiness approval has been granted. During operation, the crew should adhere to any limitations set out in the AFM and AFM supplements. Normal procedures are provided in the navigation specification, including detailed necessary crew action to be conducted during pre-flight planning, prior to commencing the procedure and during the procedure. Abnormal procedures are provided in the navigation specification, including detailed crew action to be conducted in case of on-board RNAV system failure and in case of system inability to maintain the prescribed performance of the on-board monitoring and alerting functions. The operator should have in place a system for investigating events affecting the safety of operations in order to determine their origin (coded procedure, accuracy problem, etc.). The minimum equipment list (MEL) should identify the minimum equipment necessary to satisfy the navigation application. ii. Flight crew training Each pilot must receive appropriate training, briefings and guidance material in order to safely conduct an operation. ATNS/HO/C09/30/02/01 Page 153 of July 2010

154 iii. Navigation database management Any specific requirement regarding the navigation database should be provided in the navigation specification, particularly if the navigation database integrity is supposed to demonstrate compliance with an established data quality assurance process, e.g. as specified in DO 200A/EUROCAE ED 76. c. Flight Crew and Air Traffic Operations. Pilots and air traffic controllers are the end-users of Performance-Based Navigation, each having their own expectations of how the use and capability of the RNAV system affects their working methods and everyday operations. What pilots need to know about PBN operations is whether the aircraft and flight crew are qualified to operate in the airspace, on a procedure or along an ATS route. For their part, controllers assume that the flight crew and aircraft are suitably qualified for PBN operations. However, they also require a basic understanding of area navigation concepts, the relationship between RNAV and RNP, and how their implementation affects control procedures, separation and phraseology. As importantly, an understanding of how RNAV systems work as well as their advantages and limitations are necessary for both controllers and pilots. for pilots, one of the main advantages of using a RNAV system is that the navigation function is performed by highly accurate and sophisticated on-board equipment allowing a reduction in cockpit workload and, in some cases, increased safety. in controller terms, the main advantage of aircraft using a RNAV system is that ATS routes can be straightened, as it is not necessary for routes to pass over locations marked by conventional NAVAIDS. another advantage is that RNAV-based arrival and departure routes can complement, and even replace, radar vectoring, thereby reducing approach and departure controller workload. Consequently, parallel ATS route networks are usually a distinctive characteristic of airspace in which RNAV and/or RNP applications are used. These parallel track systems can be unidirectional or bidirectional and can, occasionally, cater to parallel routes requiring a different navigation specification for operation along each route, e.g. a RNP 4 route alongside a parallel RNP 10 route. Similarly, RNAV SIDs and STARs are featured extensively in some terminal airspace. From an obstacle clearance perspective, the use of RNP applications may allow or increase access to an airport in terrain-rich environments where such access was limited or not previously possible. Air traffic controllers sometimes assume that, where all aircraft operating in a particular portion of airspace may be required to be approved at the same level of performance, these aircraft will systematically provide entirely or exactly repeatable and predictable track-keeping performance. This is not an accurate assumption because the different algorithms used in different FMS and the different ways of coding data used in the navigation database can affect the way an aircraft performs during turns. Exceptions are where radius to fix (RF) leg types and/or fixed-radius transitions (FRT) are used. Experience gained in States that have already implemented RNAV and RNP shows that such mistaken assumptions can be corrected by adequate training in Performance-Based Navigation. ATC training in RNAV and ATNS/HO/C09/30/02/01 Page 154 of July 2010

155 RNP applications is essential before implementation so as to enhance controllers understanding and confidence, and to gain ATC buy-in. PBN implementation without adequate emphasis on controller training can have a serious impact on any RNP or RNAV project schedule (see the Controller Training paragraphs in each navigation specification in Volume II of the PBN Manual, Parts B and C). i. Flight crew procedures Flight crew procedures complement the technical contents of the navigation specification. Flight crew procedures are usually embodied in the company operating manual. These procedures could include, for example, that the flight crew notify ATC of contingencies (i.e. equipment failures and/or weather conditions) that could affect the aircraft s ability to maintain navigation accuracy. These procedures would also require the flight crew to state their intentions, coordinate a plan of action and obtain a revised ATC clearance in case of contingencies. At a regional level, established contingency procedures should be made available so as to permit the flight crew to follow such procedures in the event that it is not possible to notify ATC of their difficulties. ii. ATS procedures ATS procedures are needed for use in airspace utilising RNAV and RNP applications. Examples include procedures to enable the use of the parallel offset on-board functionality or to enable the transition between airspaces having different performance and functionality requirements (i.e. different navigation specifications). Detailed planning is required to accommodate such a transition and may be achieved as follows: determining the specific points where the traffic will be directed as it transits from airspace requiring a Navigation specification with less stringent performance and functional requirements to an airspace requiring a Navigation specification having more stringent performance and functional requirements and coordinating efforts with relevant parties in order to obtain a regional agreement detailing the required responsibilities. Air traffic controllers should take appropriate action to provide increased separation and to coordinate with other ATC units as appropriate, when informed that the flight is not able to maintain the prescribed level of navigation performance. ATNS/HO/C09/30/02/01 Page 155 of July 2010

156 4.4 Implementation Guidance Introduction to Implementation Process The aim of this section is to provide a brief overview of the process to be followed when implementing RNAV or RNP applications in a given region, which might comprise a State or group of States. a. Process Overview. Three processes are provided to assist States in the implementation of PBN. They are used in sequence: Process 1 Determine requirements. Process 2 Identifying the ICAO navigation specifications for implementation. Process 3 Planning and implementation. i. Process 1 This outlines steps for a State or region to determine the strategic and operational requirements for Performance-Based Navigation via an airspace concept. Fleet equipage and CNS/ATM infrastructure in the State or region will be assessed and navigation functional requirements will be identified. ii. Process 2 This describes how a State or region determines whether implementation of an ICAO navigation specification achieves the objectives of the airspace concept, provides the required navigation functions, and can be supported by the fleet equipage and CNS/ATM infrastructure that have been identified from Process 1. Process 2 might lead to the need to review the airspace concept and required navigation functions identified in Process 1, to identify tradeoffs that would allow a better fit with a particular navigation specification detailed in the ICAO PBN Manual Doc 9813 Volume II. iii. Process 3 This provides a hands-on guide to planning and implementation, so that the navigation requirement may be turned into an implementation reality. b. Development of a New Navigation Specification. The above three processes are designed to enhance the application of harmonized global standards, and avoid proliferation of local/regional standards. Development of a new navigation specification would be considered in those very exceptional cases, where: a State or region has determined that it is not possible to use an existing ICAO navigation specification to satisfy its intended airspace concept; and it is not possible to change the elements of a proposed airspace concept so that an existing ICAO navigation specification can be used. ATNS/HO/C09/30/02/01 Page 156 of July 2010

157 Chapter 5 of the PBN Manual provides guidance for an ICAO-coordinated development of a new navigation specification. Such a development is an extensive and rigorous exercise in airworthiness and flight operations development. It should be expected to be a very complex and lengthy effort leading to a globally harmonized specification Process 1: Determine Requirements a. Introduction. The goal of Process 1 is to formulate an airspace concept and assess the existing fleet equipage and CNS/ATM infrastructure, with the overall aim of identifying the navigation functional requirements necessary to meet the airspace concept. b. Input to Process 1. The input to start this process is the strategic objectives and operational requirements stemming from airspace users (i.e. military/civil, air carrier/business/general aviation, IFR/VFR operations), and ATM requirements (e.g. airspace planners, ATC). Policy directives such as those stemming from political decisions concerning environmental mitigation can also be inputs. The process should consider the needs of the airspace user community in a broad context, i.e. IFR, VFR, military and civil aviation (e.g. air carrier, business and general aviation). Consideration should also be given to domestic and international user requirements, as well as airworthiness and operational approval for operators. The overall safety, capacity and efficiency requirements of implementation should be balanced; an analysis of all requirements, and trade-offs among competing requirements, will need to be completed. Primary and alternate means of meeting requirements should be considered; methods for communicating to airspace users the requirements and availability (and outages) of services need to be identified; and detailed planning needs to be undertaken for the transition to the new airspace concept. c. Steps in Process 1. i. Step 1: Formulate the airspace concept An airspace concept is only useful if it is defined in sufficient detail so that supporting navigation functions can be identified. The elaboration of the airspace concept is therefore best undertaken by a multi-disciplinary team as opposed to a single specialization. This team should be expected to be made up of air traffic controllers and airspace planners (from the ANSP), pilots, procedure design specialists, avionics specialists, flight standards and airworthiness regulators, and airspace users. Together, this team would develop the airspace concept using the broad directions provided by the strategic objectives. ATNS/HO/C09/30/02/01 Page 157 of July 2010

158 (1) Factors that would be detailed include: Airspace organisation and management (i.e. ATS route placement, SIDs/STARs, ATC sectorisation); Separation minima and route spacing; Instrument approach procedure options; How ATC is to operate the airspace; Expected operations by flight crew; and Airworthiness and operational approvals. This team will focus their efforts on the following; Airspace User Requirements Airspace Requirements Approach Requirements Other Requirements Expanded information for the team s consideration may be found in the PBN Manual Doc Volume II Attachment A. ii. Step 2: Assessment of existing fleet capability and available NAVAID Infrastructure Planners must understand the capability of the aircraft that will be flying in the airspace in order to determine the type of implementation that is feasible for the users. Understanding what is available in terms of NAVAID infrastructure is essential to determining how and if a navigation specification can be supported. The following considerations should be taken into account. (1) Assessing aircraft fleet capability, and (2) Assessing NAVAID infrastructure It is important that implementing a RNAV application does not in itself become the cause for installing new NAVAID infrastructure. The introduction of RNAV applications could result in being able to move some existing NAVAIDS (e.g. DMEs may be relocated when they no longer have to be co-located with VOR). iii. Step 3: Assessment of the existing ATS surveillance system and communications infrastructure and the ATM system. An air traffic system is the sum of the CNS/ATM capabilities available. PBN is only the navigation component of CNS/ATM. It cannot be safely and successfully implemented without due consideration of the communication and ATS surveillance infrastructure available to support the operation. For example, a RNAV 1 route will require different ATS route spacing in a radar environment to that in a non-radar environment. The availability of communications between the aircraft and air traffic service provider may impact the level of air traffic intervention capability needed for safe operations. The following considerations should be taken into account. (1) ATS surveillance infrastructure (2) Communication infrastructure (3) ATM systems ATNS/HO/C09/30/02/01 Page 158 of July 2010

159 iv. Step 4 Identify necessary navigation performance and functional requirements It should be noted that the decision on the choice of a RNAV or RNP navigation specification as defined by the ICAO is not only determined by aircraft performance requirements (e.g. accuracy, integrity, continuity, availability), but may also be determined by the need for specific functional requirements (e.g. leg transitions/path terminators, parallel offset capabilities, holding patterns, navigation databases). The proposed navigation functional requirements also need to consider: the complexity of RNAV procedures envisaged; the number of waypoints needed to define the procedure; the spacing between waypoints and the need to define how a turn is executed; and whether the procedures envisaged aim simply to connect with the en-route operations and can be restricted to operations above minimum vectoring altitude/minimum sector altitude, or are the procedures expected to provide approach guidance The next stage is Process 2, where the effort is made to identify the appropriate ICAO navigation specification for implementation Process 2: Identifying the ICAO Navigation Specification for Implementation a. Introduction. The goal of Process 2 is to identify the ICAO navigation specification(s) that will support the airspace concept and navigation functional requirements as defined in Process 1. b. Input to Process 2. The navigation functional requirements, fleet capability, and CNS/ATM capabilities will have been identified in Process 1. These will provide the specific context against which the planners will evaluate their ability to meet the requirements of a particular ICAO navigation specification. ATNS/HO/C09/30/02/01 Page 159 of July 2010

160 c. Steps in Process 2. i. Step 1: Review the ICAO navigation specifications in Volume II of the PBN Manual. The first step in Process 2 is aimed at finding a potential match between the requirements identified in Process 1 and those contained in one or more of the ICAO navigation specifications in Volume II. In reviewing one or more possible ICAO navigation specifications, planners will need to consider the output of Process 1 with respect to: (1) the ability of the existing aircraft fleet and available NAVAID infrastructure to meet the requirements of a particular ICAO navigation specification, and (2) the capabilities of their communications and ATS surveillance infrastructure, and ATM system to support implementation of this particular ICAO navigation specification. ii. Step 2: Identify appropriate ICAO navigation specification to apply in the specific CNS/ATM environment. If planners determine that a particular ICAO navigation specification can be supported by the fleet equipage, NAVAID infrastructure, communications and ATS surveillance and ATM capabilities available in the State, proceed to Process 3: Planning and implementation. If an ICAO navigation specification cannot be supported, continue with Process 2, Step 3. iii. Step 3: Identify trade-offs with airspace concept and navigation functional requirements (if necessary). This step is followed when an exact match between a particular ICAO navigation specification and the fleet equipage, NAVAID infrastructure, communications and ATS surveillance and ATM capabilities available in the State cannot be made. It is aimed at changing either the airspace concept or navigation functional requirements, in order to select an ICAO navigation specification. For example, operational requirements reflected in the airspace concept could be reduced, or alternate means identified to achieve a similar (if not identical) operational result. ATNS/HO/C09/30/02/01 Page 160 of July 2010

161 Planners should revisit the airspace concept and required navigation functions identified in Process 1 to determine what trade-offs can be made, so as to implement a particular existing ICAO navigation specification. In most instances it will be possible to make sufficient trade-offs in the original airspace concept or required navigation functions from Process 1 that an existing ICAO navigation specification can then be selected. Once trade-offs have been made that will allow selection of an ICAO navigation specification, proceed to Process 3: Planning and implementation. However, if in the rare case that a State determines that it is impossible to make trade-offs in its airspace concept and/or navigational functional requirements, the State would have to develop a new navigation specification (discussed in the PBN Manual, Chapter 5, the ICAO Doc. 9813) Process 3: Planning and Implementation a. Introduction. The process described in this chapter is concerned with planning and implementing Performance-Based Navigation. It follows upon completion of Process 1 and 2. See Inset for a detailed discussion of some important considerations planners should keep in mind when framing the implementation plan. Inset Implementation considerations In applying one of the ICAO navigation specifications for oceanic, remote continental and continental en-route operations as described in the PBN Manual Volume II, consideration should be given to the need for regional or multi-regional agreement. This is because connectivity and continuity with operations in adjoining airspace need to be considered to maximize benefits. For terminal and approach operations, the implementation of an ICAO navigation specification in the PBN Manual is more likely to occur on a single-state basis. Some TMAs are adjacent to national borders for which multinational coordination would likely be required. Where compliance with an ICAO navigation specification is prescribed for operation in an airspace or ATS routes, these requirements are to be indicated in the State s AIP. The decision to mandate a requirement for one or more ICAO RNAV or RNP specifications should only be considered after several factors have been taken into account. These include, but are not limited to: the operational requirements of the airspace users (civil/military, IFR operations), as well as those of ANSPs; regulatory requirements at both international and national levels; the proportion of the aircraft population currently capable of meeting the specified requirements, and the cost to be incurred by operators that need to equip aircraft to meet the requirements of the navigation specification; the benefits in terms of safety, capacity, improved access to airspace/airports or environment to be derived from implementing the airspace concept; the impact on operators in terms of additional flight crew training; the impact on flight crew in terms of workload; and the impact on air traffic services in terms of controller workload and required facilities, (including automation and flight plan processing changes). Particular attention must be given to possible workload and efficiency impacts of operating mixed navigation environments. ATNS/HO/C09/30/02/01 Page 161 of July 2010

162 i. Step 1: Formulate safety plan. The first step in Process 3 is the formulation of a safety plan for the PBN implementation. Guidance for formulating a safety plan can be found in Safety Management Manual (SMM) (ICAO Doc 9859). Depending on the nature of the implementation, this could be a State or regional safety plan. Normally, such a plan would be developed together with an ANSP safety bureau to the satisfaction of the regulatory authority. This safety plan details how the safety assessment is to be accomplished for the proposed RNAV or RNP implementation. ii. Step 2: Validate airspace concept for safety. Validation of an airspace concept involves completing a safety assessment. From this assessment, additional safety requirements may be identified which need to be incorporated into the airspace concept prior to implementation. Four validation means are traditionally used to validate an airspace concept: airspace modelling; fast-time simulation (FTS); real-time simulation (RTS); live ATC trials. For simple airspace changes, it may be unnecessary to use all of the above validation means for any one implementation. For complex airspace changes, however, FTS and RTS can provide essential feedback on safety (and efficiency) issues and their use is encouraged. Application of new navigation specifications can range from simple through major changes to the airspace concept. All four types of validation are further discussed in the PBN Manual. iii. Step 3: Procedure design. A total system approach to the implementation of the airspace concept means that the procedure design process is an integral element. Therefore, the procedure designer is a key member of the airspace concept development team. Procedure designers need to ensure that the procedures can be coded in ARINC 424 format. Currently, this is one of the major challenges facing procedure designers. Many are not familiar with neither the path & terminators used to code RNAV systems or the functional capabilities of different RNAV systems. Many of the difficulties can be overcome, however, if close cooperation exists between procedure designers and the data houses that provide the coded data to the navigation database providers. Once these procedures have been validated and flight inspected (see Steps 4 and 6), they are published in the national AIP along with any changes to routes, holding areas, or airspace structures. The complexity involved in data processing for the RNAV system database means that in most instances, a lead period of two AIRAC cycles is required (see PBN Manual Doc Volume I Attachment B, Section 3 for more details). ATNS/HO/C09/30/02/01 Page 162 of July 2010

163 iv. Step 4: Procedure ground validation. The development of a RNAV or RNP instrument flight procedure or ATS route follows a series of steps from the origination of data through survey to the final publication of the procedure and subsequent coding of it for use in an airborne navigation database. At each step of the procedure design process, there should be quality control procedures in place to ensure that the necessary levels of accuracy and integrity are achieved and maintained. These procedures are detailed in PANS-OPS (Doc 8168), Volume II. After designing the procedure and before a RNAV or RNP route or procedure is published, PANS-OPS (Doc 8168) require that each procedure undergo a validation process. The objective of validation is to: (1) provide assurance that adequate obstacle clearance has been provided; (2) verify that the navigation data to be published, as well as that used in the design of the procedure, are correct; (3) verify that all required infrastructure, such as runway markings, lighting, and communications and navigation sources, are in place and operative; (4) conduct an assessment of fly ability to determine that the procedure can be safely flown; and (5) evaluate the charting, required infrastructure, visibility and other operational factors. Many of these factors can be evaluated, entirely or in part, during ground validation. Initial fly ability checks should be conducted with software tools allowing the fly ability of the procedure to be confirmed for a range of aircraft and in a full range of conditions (wind/temperature, etc.) for which the procedure is designed. The verification of the fly ability of a RNAV or RNP procedure can also include independent assessments by procedure designers and other experts using specialised software or full-flight simulators. Fly ability tests using flight inspection aircraft can be considered, but it must be borne in mind that this only proves that the particular aircraft used for the test can execute the procedure correctly. This is probably acceptable for the majority of less complex procedures. The size and speed of flight test aircraft can seldom fully represent the performance of a fully loaded B747 or A340 and therefore simulation is considered the most appropriate way to carry out the fly ability test. Flight simulator tests should be conducted for those more complex procedures, such as RNP AR APCH, when there is any indication that fly ability may be an issue. Software tools that use digital terrain data (typically digital terrain elevation data (DTED) level 1 being required) are available to confirm appropriate theoretical NAVAID coverage. v. Step 5: Implementation decision. It is usually during the various validation processes described above that it becomes evident whether the proposed design can be implemented. The decision whether or not to go ahead with implementation needs to be made. Note: If the available tools and/or quality of data used in Step 4 warrant, it may be desirable to undertake Step 6 before a final implementation decision is taken. ATNS/HO/C09/30/02/01 Page 163 of July 2010

164 The decision on whether to go ahead with implementation or not will be based on certain deciding factors. These include: (1) whether the ATS route/procedure design meets air traffic and flight operations needs; (2) whether safety and navigation performance requirements have been satisfied; (3) pilot and controller training requirements; (4) whether changes to flight plan processing, automation, or AIP publications are needed to support the implementation. If all implementation criteria are satisfied, the project team needs to plan for execution of the implementation, not only as regards their own airspace and ANSP, but in cooperation with any affected parties which may include ANSPs in an adjacent State. vi. Step 6: Flight inspection and flight validation. Flight inspection of NAVAIDs involves the use of test aircraft which are specially equipped to gauge the actual coverage of the NAVAID infrastructure required to support the procedures, arrival and departure routes designed by the procedure design specialist. Flight validation continues the procedure validation process noted in Step 4. It is used to confirm the validity of the terrain and obstruction data used to construct the procedure, and that the track definition takes the aircraft to the intended aiming point, as well as the other validation factors listed in Step 4. Output from the above procedures may require the procedure design specialist to refine and improve the draft procedures. The Manual on Testing of Radio Navigation Aids (ICAO Doc 8071) provides general guidance on the extent of testing and inspection normally carried out to ensure that radio navigation systems meet the SARPs in Annex 10 Aeronautical Telecommunications, Volume I. PANS-OPS (ICAO Doc 8168), Volume II, Part 1, Section 2, Chapter 4, Quality Assurance provides more detailed guidance on instrument flight procedure validation. vii. Step 7: ATC system integration considerations. The new airspace concept may require changes to the ATC system interfaces and displays to ensure controllers have the necessary information on aircraft capabilities. Considerations arising from mixed equipage scenarios are discussed in the PBN Manual. Such changes could include, for example: (1) modifying the air traffic automation s flight data processor (FDP); (2) making changes, if necessary, to the radar data processor (RDP); (3) requiring changes to the ATC situation display; and (4) requiring changes to ATC support tools. There may be a requirement for changes to ANSP methods for issuing NOTAMS. ATNS/HO/C09/30/02/01 Page 164 of July 2010

165 viii. Step 8: Awareness and training material. The introduction of PBN can involve considerable investment in terms of training, education and awareness material for both flight crew and controllers. In many States, training packages and computer-based training have been effectively used for some aspects of education and training. The ICAO provides additional training material and seminars. Each navigation specification in the PBN Manual, Volume II, Parts B and C addresses the education and training appropriate for flight crew and controllers. ix. Step 9: Establishing operational implementation date. The State establishes an effective date in accordance with the requirements set out in the PBN Manual, Volume I, Attachment B, Data Processes. Experience has identified that an additional time period (e.g. one to two weeks) should be allocated prior to the operational implementation date. This additional period is to ensure ground and airborne system data are properly loaded and validated in databases. x. Step 10: Post-implementation review. After the implementation of PBN, the system needs to be monitored to ensure that safety of the system is maintained and to determine whether strategic objectives have been achieved. If after implementation, unforeseen events do occur, the project team should put mitigation measures in place as soon as possible. In exceptional circumstances, this could require the withdrawal of RNAV or RNP operations while specific problems are addressed. A system safety assessment should be conducted after implementation and evidence collected to verify that the safety of the system is assured (see the Safety Management Manual (SMM) ICAO Doc 9859). ATNS/HO/C09/30/02/01 Page 165 of July 2010

166 4.4.5 Guidelines for Development of a New Navigation Specification a. Introduction. In most instances, it will be possible to use an existing ICAO navigation specification from PBN Manual Doc Volume II to satisfy the navigation requirements for a State or region s planned airspace concept. In the rare case that a State or region is not able to complete Process 2 and select an ICAO navigation specification, the State or region would have to develop a new navigation specification. In order to avoid proliferation of regional standards, a new navigation specification would be subject to the ICAO review, and ultimately be available for global application. There are guidelines in the PBN Manual that address this situation. Development of a new navigation specification should only be undertaken if it becomes impossible to make acceptable trade-offs between the defined airspace concept and navigational functional requirements that can be supported by a standard ICAO navigation specification. It should be recognised that development of a new navigation specification involves a rigorous evaluation of navigation equipment and its operation. This will require even greater involvement by airworthiness authorities than required in Process 2. While a considerable amount of the preparatory work for development of a new navigation specification would initially be undertaken as part of Processes 1 and 2, the State or region concerned must undertake a full analysis at every step. Review and modifications to the work done in Processes 1 and 2 may also need to be accomplished in whole or in part. b. Steps for developing a new Navigation Specification. i. Step 1: Feasibility assessment and business case. When developing a new navigation specification, the question of the feasibility of establishing a new navigation specification that can realistically be met by aircraft manufacturers and operators, and achieving cost-effective implementation of that navigation specification, is particularly important. It is necessary to undertake a feasibility assessment and to develop a business case. The business case assesses the benefits to be derived from the proposed airspace concept and the cost of implementing a new navigation specification. The cost information will be derived from the proposed functions included in the planned new navigation specification, together with estimates of installation and certification costs. It should be understood that the timescales from initial definition of a new requirement to availability in new RNAV or FMS systems can be in excess of five to seven years. Development from this point to one where the majority of the aircraft fleet operating in a given airspace by natural (non-mandated) upgrading of the RNAV equipment can be in excess of 15 years. Thus, development of a new navigation specification normally involves using navigation functional requirements already provided by manufacturers without the existence of certification or operational approval. ATNS/HO/C09/30/02/01 Page 166 of July 2010

167 (1) Outline of a new navigation specification The outline is a product of the business case and has to take due account of the functional requirements needed to meet the airspace concept. It has to be produced with sufficient detail to enable aircraft manufacturers to prepare cost estimates for the upgrades to RNAV systems (including RNP systems). ii. Step 2: Development of a navigation specification. Contact should be made early with the ICAO in identifying the airspace concept that is to be introduced and the foreseen need for a new navigation specification. The role of the ICAO in this process will be to support the State or region in a detailed review of its requirements, in order to ensure subsequent global acceptability of the new navigation specification. Starting from the airspace concept which developers identified at the beginning of their PBN implementation efforts, it will then be necessary to detail the requirements against which the aircraft and its operation will ultimately be approved. In its coordinating role, the ICAO will be able to identify other States or regions which may be in the process of developing a new navigation specification with similar operational and/or navigational functions. In this situation, the ICAO will support multi-state or multi-regional development of a new harmonised navigation specification. Once the new navigation specification is complete, it will ultimately be incorporated into the PBN Manual, Volume II. Although the airspace concept and navigation functional requirements developed in Process 1 form the starting point of the development of a new navigation specification, it is likely that these will need iterative refinement, in order to align them with the details of the new navigation specification as it is being developed. iii. Step 3: Identification and development of associated ICAO provisions. The development of a new navigation specification may require the development of new ICAO provisions, for example, procedure design (PANS-OPS (ICAO Doc 8168)) criteria or ATM procedures. While these tasks are formally carried out by experts, a State(s) or region(s) would be expected to identify changes that need to be introduced to enable the new navigation specification and applications. iv. Step 4: Safety assessment. In accordance with the provisions included in the ICAO Annex 11 Air Traffic Services and PANS-ATM (ICAO Doc 4444), a full safety assessment of the new navigation specification should be completed (see the Safety Management Manual (SMM) (Doc 9859). This safety assessment is undertaken once the new navigation specification is sufficiently mature. See PBN Manual, Volume II, Part A, Chapter 2 Safety Assessment, for a more detailed discussion of the necessary elements of safety assessment and risk modelling. v. Step 5: Follow-up. Where the above evaluation leads to the conclusion that the proposed new navigation specification can be applied in the ATM environment, the State or region will be required to formally notify the ICAO of the proposed application. The ICAO will take action to include the new navigation specification into Volume II of the PBN manual. ATNS/HO/C09/30/02/01 Page 167 of July 2010

168 Upon completion of the new navigation specification development, the State or region would then continue with Process 3: Planning and implementation. ATNS/HO/C09/30/02/01 Page 168 of July 2010

169 5 CHANGES IN ATS DELIVERY DUE TO PBN IMPLEMENTATION Air traffic controllers and other air traffic services providers become involved with PBN at a tactical level, as they and pilots use the PBN concept in real-time operations. They rely on the preparatory work completed at strategic level by other stakeholders (i.e. airspace planners, procedure designers and regulatory authorities). This section will address only the basic changes expected in the provision of ATS, as specific procedures will only be developed at a later stage in accordance with the PBN Implementation Roadmap. 5.1 ATS Flight Plan Requirements As discussed in previous sections, aircraft should be equipped with a RNAV system able to support the desired navigation application. The RNAV system and aircraft operations must be compliant with regulatory material that reflects the navigation specification developed for a particular navigation application and approved by the appropriate regulatory authority for the operation. This approval is indicated to ATS by inserting appropriate designations in Item 10 (Equipment) on the ATS Flight Plan. Radio communication, navigation and approach aid equipment is indicated in Item 10 of the ATS flight plan as follows: ATNS/HO/C09/30/02/01 Page 169 of July 2010

170 Insert one letter as follows: N S If no COMM/NAV/Approach aid equipment for the route flown is carried, or the equipment is unserviceable; OR If standard COM/NAV/Approach aid equipment for the route to be flown is carried and serviceable (standard equipment in the RSA is considered to be VHF RTF, ADF, VOR and ILS). AND/OR Insert one or more of the following letters to indicate the COM/NAV/Approach aid equipment available and serviceable: A B C D E F G H I (Not allocated) (Not allocated) LORAN C DME (Not allocated) ADF GNSS HF RTF Inertial Navigation J Data Link (Specify in Item 18 the equipment carried, preceded by DAT/ followed by one or more letters as appropriate.) K L M O P Q R T U V W X Y S MLS ILS Omega VOR (Not allocated) (Not allocated) RNP type certification (Inclusion of letter R indicates that an aircraft meets RNP type prescribed for the route segment(s), route(s) and/or area concerned.) TACAN UHF RTF VHF RTF } When prescribed by ATS Other equipment carried (Specify in Item 18 the other equipment carried. Preceded by COM/ and/or NAV/, as appropriate.) ATNS/HO/C09/30/02/01 Page 170 of July 2010

171 5.1.1 Conventional Navigation When aircraft use conventional navigation, aircraft normally navigate using external electronic guidance or self-contained information; external guidance is provided by ground-based NAVAIDs or from GNSS; and traditional route structures are followed between the NAVAIDs. NAVAIDs used include NDBs and VORs, and routes are defined by geographical positions of NAVAIDs or fixes based on the intersection of radial from two NAVAIDs or a distance and a bearing from one. Aircraft are required to overfly these NAVAIDs and fixes. Conventional Navigation via ground-based NAVAIDs Non-Conventional Navigation Area Navigation (RNAV) is a method of navigation which permits aircraft operation on any desired flight path within the coverage of station-referenced navigation aids or within the limits of the capability of self-contained aids, or a combination of these. Area Navigation Aircraft fly desired path ATNS/HO/C09/30/02/01 Page 171 of July 2010

172 5.1.3 Designation of RNAV Routes RNAV routes are defined by significant points called Waypoints, which are, in turn, defined by co-ordinates. These routes can follow any desired path and are not constrained by the position of ground-based NAVAIDs. In the example below, the RNAV route uses DME/DME as the NAVAID to provide positional information: Each point on the desired route is characterised by ranges from a pair of DMEs. The aircraft s computer (e.g. FMS) will estimate its position and provide guidance to the track. A position is estimated by the ranges from two suitably situated DMEs. Two range rings will give two possible positions, but the navigation computer will exclude the point of ambiguity. Track Position 1 ATNS/HO/C09/30/02/01 Page 172 of July 2010

173 Track Position ATS Procedures RNAV implementation allows ATC the possibility for the systematic use of DIRECT TO in the overall management of air traffic as all RNAV certified aircraft are capable to execute DIRECT TO waypoints. Where appropriate, ATC could consider DIRECT TO as an alternative to radar vectoring for RNAV capable aircraft as the use of DIRECT TO instead of radar vectoring allows RNAV systems to maintain distance to go information. The following advantages will be derived: The RNAV system and pilot are aware of distance to touch down for aircraft management, and RNAV-equipped aircraft may derive maximum benefit from RNAV systems in terms of optimised flight management and performance. However, be aware that pilots may not be able to comply with a DIRECT TO for any of the following reasons: Navigation computer problem, Too close to waypoint specified, Angle of turn/speed too great, Waypoint not displayed on the FMS for pilot selection, Waypoint not part of SID/STAR, and/or SID/STAR not assigned. ATNS/HO/C09/30/02/01 Page 173 of July 2010

174 If pilots are unable to comply, they will probably request radar vectors, but be aware that large turns close to the waypoint or at high speed, may result in the aircraft overshooting the next leg Control Procedures (FUTURE DEVELOPMENT) a. Aerodrome (including Tower Control, Ground Control and Clearance Delivery) b. Approach - Procedural, Radar and Automatic Dependant Surveillance (ADS) c. Area - Procedural, Radar and ADS (including Flight Information Service & Oceanic) d. Central Airspace Management Unit (CAMU) and the Briefing Office Contingency Procedures The pilot must notify ATC when the RNAV performance ceases to meet the requirements for RNAV. The communication to ATC must be in accordance with the authorised procedures. In the event of communication failure, the flight crew should continue with the flight plan in accordance with the published lost communication procedure. The pilot must notify ATC of any loss of RNAV capability, together with the proposed course of action. The loss of RNAV capability includes any failure or event causing the aircraft to no longer satisfy the RNAV requirements of the route. Where stand-alone GNSS equipment is used: In the event that there is a loss of RAIM detection function, the GNSS position may continue to be used for navigation. The flight crew should attempt to cross-check the aircraft position, with other sources of position information, (e.g. VOR, DME and/or NDB information) to confirm an acceptable level of navigation performance. Otherwise, the flight crew should revert to an alternative means of navigation and advise ATC. In the event that the navigation display is flagged invalid due to a RAIM alert, the flight crew should revert to an alternative means of navigation and advise ATC. (FUTURE DEVELOPMENT) a. Aerodrome (including Tower Control, Ground Control and Clearance Delivery) b. Approach - Procedural, Radar and Automatic Dependant Surveillance (ADS) c. Area - Procedural, Radar and ADS (including Flight Information Service & Oceanic) d. Central Airspace Management Unit (CAMU) and the Briefing Office e. Contingency Procedures relating to Mach Number Technique ATNS/HO/C09/30/02/01 Page 174 of July 2010

175 5.3 Separation Minima Vertical and horizontal (lateral and longitudinal) separation minima as per ICAO Doc 4444 and SA CAA ATS Standards and Procedures Manual (as amended) are to be applied in the provision of ATS to aircraft utilising PBN Longitudinal (FUTURE DEVELOPMENT) Lateral (FUTURE DEVELOPMENT) 5.4 Mixed Equipage Environment A mixed navigation environment introduces some complexity for ATS. From an ATC workload and associated automation system perspective, the system needs to include the capability of filtering different navigation specifications from the ATC flight plan and conveying relevant information to controllers. For ATC, particularly under procedural control, different separation minima and route spacing are applied as a direct consequence of the navigation specification. Mixed navigation environments usually occur in one of three scenarios: One RNAV or one RNP application has been implemented (but not as a mandate), and conventional navigation is retained. An example of this would be if RNAV 1 were the declared RNAV specification for a Terminal Airspace, with the availability also of procedures based on conventional navigation, for those aircraft not RNAV 1 approved. A mixed-mandate is used within an airspace volume, usually en-route or oceanic/remote procedural operations. For example, it is mandatory to be approved to a RNAV 1 specification for operation along one set of routes, and Basic RNP 1 along another set of routes within the same airspace; A mix of RNAV and RNP applications is implemented in airspace, but there is no mandate for operators to be able to perform them. Here again, conventional navigation could be authorised for aircraft that are not approved to any of the navigation specifications. Mixed navigation environments can potentially have a negative impact on ATC workload, particularly in dense en-route and terminal area operations. The acceptability of a mixed navigation environment to ATC is also dependent on the complexity of the ATS route or SID and STAR route structure and upon availability and functionality of ATC support tools. The increased ATC workload normally resulting from mixed mode operations has resulted in the need to limit mixed-mode operations to a maximum of two types where there is one main level of capability. In some cases ATC has been able to accept a mixed environment where 90% of the traffic is approved to the required navigation specification; whereas in other instances, a 70% rate has been workable. For these reasons, it is crucial that operations in a mixed navigation environment be properly assessed in order to determine the viability of such operations. ATNS/HO/C09/30/02/01 Page 175 of July 2010

176 5.5 Transition between Different Operation Environments (FUTURE DEVELOPMENT) 5.6 Phraseology RTF phraseologies for RNAV are to be used as follows; When checking if aircraft is able to accept a SID/STAR, ATC will use ADVISE IF ABLE (designator) DEPARTURE [or ARRIVAL] e.g. KLM123 ADVISE IF ABLE SNAKE ONE ALPHA ARRIVAL. If aircraft is unable to accept ATC issued RNAV SID/STAR, pilot will use UNABLE (designator) DEPARTURE [or ARRIVAL] DUE RNAV TYPE e.g. KLM921 UNABLE BILBO ONE ALPHA ARRIVAL DUE RNAV TYPE, KLM921. In this case ATC will seek to provide an alternative routeing. If aircraft is unable to continue with RNAV operations due to some failure or degradation of the RNAV system, pilot will use UNABLE RNAV DUE EQUIPMENT. Aircraft in flight which announce to ATC loss of RNAV capability should be provided with radar vectors, routed via conventional routes or routed direct to conventional NAVAIDs. For arriving aircraft in the TMA, radar vectors could be the most efficient reversionary means. If ATC is unable to assign a RNAV SID/STAR requested by a pilot, for reasons associated with the type of on-board RNAV equipment indicated on the FPL, ATC shall inform the pilot using UNABLE TO ISSUE (designator) DEPARTURE [or ARRIVAL] DUE RNAV TYPE. 5.7 Reporting of Gross Navigational Errors Gross Navigational Errors (GNEs) must be reported to the relevant regulatory authority as a condition of approval. GNEs are defined as: Horizontal navigation errors of 25 NM or more; Vertical navigation errors of 300 ft or more; Longitudinal navigation errors of three minutes or more variation between the aircraft s estimated time of arrival at a reporting point and its actual time of arrival; and Navigation system failures. Most common causes of GNEs are failure to follow clearance, incorrect waypoint entry, climb or descent without clearance and ATC misunderstanding. To avoid GNEs, pilots are encouraged to following these best practises: Good cockpit SOPs, Verify clearances, and Check position ten minutes after crossing waypoint. ATNS/HO/C09/30/02/01 Page 176 of July 2010

177 5.8 RNAV STARs and SIDs RNAV systems dynamically update the active waypoints. As waypoints are passed, they are removed from the active waypoints list. Therefore, be aware that aircraft can have considerable difficulty manoeuvring DIRECT TO a waypoint which is considered by the RNAV system, to have been passed. ATC should make use of DIRECT TO instructions only for waypoints on the assigned SID/STAR, and DIRECT TO should only be used for waypoints ahead of the aircraft. If the pilot has been cleared for a SID/STAR and ATC consequently have to issue a DIRECT TO a waypoint that is part of the SID/STAR, the following applies: The pilot selects the waypoint in the FMS, The FMS and navigation display are updated maintaining all details of the route from the DIRECT TO waypoint onwards, and The aircraft continues with the SID/STAR after reaching the waypoint. The aircraft is expected to meet level restrictions if published, if the cleared level makes this possible. The aircraft is also expected to meet speed restrictions if published. Be aware however, that a DIRECT TO could shorten track miles to the waypoint, which could have an impact on the aircraft s ability to meet level and speed restrictions. If the pilot has been cleared for a SID/STAR and ATC consequently have to issue a DIRECT TO a waypoint that is not part of the SID/STAR, the following applies: Waypoints not held in the navigational database are not to be manually inserted for aircraft operations in the TMA. It will take time for the pilot to retrieve the waypoint from the database. The clearance for the SID/STAR is cancelled and previously loaded SID/STAR is dropped from the RNAV system. No further routeing is maintained or displayed. The aircraft requires explicit routeing after the waypoint from ATC. If no further explicit routeing information from ATC is received, the RNAV system will revert to present heading mode after reaching the waypoint. That means that the aircraft will continue on from the waypoint on the heading it is on when it arrives there, unless otherwise instructed. Be aware that the aircraft reaction could be delayed and that this process is prone to error, therefore ATC should rather consider the use of radar vectors if routeing away from a SID/STAR is required. ATNS/HO/C09/30/02/01 Page 177 of July 2010

178 5.8.1 Related Control Procedures The use of RNAV does not change existing ATC and pilot responsibilities. It does not relieve: Pilots of their responsibility to ensure that any clearances are safe in respect to terrain clearance. ATC of its responsibility to assign levels which are at or above established minimum flight altitudes. The pilot still remains responsible for terrain clearance. When an IFR flight is being radar vectored by ATC or is given a direct routeing off an ATS route, the radar controller shall issue clearances such that the prescribed obstacle clearance exists, the pilot must also ensure flight operations conform to published minimum flight altitudes and must inform ATC of any inability to accept a clearance or instruction on the basis of terrain clearance issues Radar Vectoring Techniques If minimum radar vectoring altitudes are to be used by ATC as the basis for assigning levels in conjunction with RNAV clearances/instructions, a Radar Minimum Altitude Chart should be published to allow pilots to comply with their responsibilities with regard to terrain avoidance. Note: Be aware that RNAV DIRECT TO instructions are not radar vectors. If ATC issues radar vectors whilst an aircraft is flying a RNAV SID/STAR, ATC should be aware that the pilot may require considerable manipulation of the RNAV system in order to resume a SID/STAR cancelled by ATC, (i.e. the pilot may have difficulty in establishing the actual sequence of active waypoints, as a function of the aircraft s position). Graphic by Eurocontrol Graphic by Eurocontrol ATNS/HO/C09/30/02/01 Page 178 of July 2010

179 For arriving aircraft, if radar vectoring is initiated, ATC should consider continuing with radar vectoring until the aircraft intercepts the final approach aid, e.g. ILS. If radar vectoring is initiated for departing aircraft, ATC should consider remaining with radar vectoring until the aircraft is in a position to join the en-route ATS route structure, or issuing a DIRECT TO the last waypoint of the RNAV SID Open and Closed STARs PBN makes it possible to design closed or open STARs. Although open or closed STARs are not the ICAO expressions, these terms are increasingly common in use. The choice of open or closed procedure needs to take account of the actual operating environment and must take into account ATC procedures. Open STARs provide track guidance (usually) to a downwind track position from which the aircraft is tactically guided by ATC to intercept the final approach track. An open STAR will require tactical routeing instructions to align the aircraft with the final approach track. This results in the RNAV system being able to descend only to the final point on the procedure and, where path stretching is applied by ATC, will impact the ability of the RNAV system to ensure a continuous descent profile. Graphic by Eurocontrol Graphic by Eurocontrol Closed STARs provide track guidance right up to the final approach track whereupon the aircraft usually intercepts the ILS. The closed STAR provides the pilot with a defined distance to touch down thus supporting the RNAV system s execution of the vertical profile. Where multiple arrival routes are operated onto a single runway, the closed procedure can result in a safety hazard should ATC not be able to intervene to prevent the automatic turn onto final approach towards other traffic. Significantly, however, closed STARs can be designed and published in a manner that anticipates alternative routeing to be given by ATC on a ATNS/HO/C09/30/02/01 Page 179 of July 2010

180 Graphic by Eurocontrol tactical basis. These tactical changes may be facilitated by the provision of additional waypoints allowing ATC to provide path stretching or reduction by the use of instructions direct to a waypoint. However, these tactical changes, needed to maximise runway capacity, do impact on the vertical profile planned by the RNAV system Altitude Constraints (FUTURE DEVELOPMENT) Descend/Climb Clearances Three main categories of level information are used, i.e. minimum flight altitudes, cleared levels and level restrictions. Minimum flight altitudes (MFAs) can be considered as: Minimum sector altitudes (MSAs) Minimum radar vectoring altitudes (MRVAs) Area minimum altitudes (AMAs) Minimum flight altitudes published for segments of SIDs and STARs. MFAs are calculated to ensure safe terrain clearances. It should be noted that currently it is not mandatory to publish MRVAs, although it is recommended by the ICAO. Cleared levels could be published as a written CLIMB TO/DESCEND TO (level), ATC expect aircraft to climb/descend to that level. These are mostly published as elements of SIDs and have limited application for STARs. Explicitly cleared levels are issued by ATC on RTF and override published cleared levels. ATNS/HO/C09/30/02/01 Page 180 of July 2010

181 Graphic by Eurocontrol Level restrictions are shown on charts in conjunction with waypoints where required, but do not represent authorisation to climb/descend to that level, as it is published for purposes of strategic airspace/traffic segregation. Pilots must comply with level restrictions to the extent the cleared level makes it possible. For arriving aircraft, published level restrictions, which are at or above the cleared level which is in effect, shall be complied with. For departing aircraft, published level restrictions, which are at or below the cleared level which is in effect, shall be complied with. 5.9 RNP Approach and Related Procedures Waypoint speed restrictions may be published on charts in conjunction with selected waypoints where required. ATC is free to cancel published speed restrictions at their own discretion. Explicit speed restrictions override published ones. Be aware that adjusting speeds could have an impact on turn performance (track) and vertical profiles Impact of Requesting a Change to Routing during a Procedure (FUTURE DEVELOPMENT) 5.11 Fix/Waypoint Naming In the ICAO Annex 11 and Doc 8168, the term waypoint is only used to define RNAV routes and flight paths of aircraft employing RNAV systems, while the term significant point is used, in Annex 11, to describe a specified geographical location used in defining an ATS route or the flight path of an aircraft and for other navigation and ATS purposes. It follows from this definition that all waypoints are significant points, even when additional waypoints are established for RNAV procedures on, or off-set from, the arrival/approach tracks, to allow the ATS provider to de-conflict and sequence RNAV traffic. ATNS/HO/C09/30/02/01 Page 181 of July 2010

182 In many other documents, a waypoint is also described as a fix. This is especially the case in the terminal area where the initial approach fix (IAF), the intermediate fix (IF), the final approach fix (FAF) and the missed approach holding fix (MAHF) are commonly used terms. In order to avoid confusion, the ICAO has decided to continue to use the terms IAF, IF, FAF and MAPt in both conventional and RNAV instrument approach definitions. As a general principal, the procedure designer should ensure that all RNAV waypoints are named and that the published names are appropriate for use in the navigation database. Navigation databases can hold waypoint names but usually operate with waypoint (fix) identifiers which are five characters long, known as the 5 Letter Name Code (5LNC). The ICAO requires that all significant points are identified by 5LNCs. However, waypoints marked by the site of a NAVAID, should have the same name and coded designator as the NAVAID. NAVAIDs are usually annotated with the associated three-letter designator on the aircraft displays but 5LNCs should be used where three-letter designators are not available. While the responsibility for issuing waypoint names lies with the ICAO regional office, individual States should exercise great care when selecting new waypoint or NAVAID names to ensure that they are not already in use. The following table provides guidelines for naming waypoints: Area of Application General Usage Name Type En-route waypoints Final waypoint SID Initial waypoint STAR Waypoints common to more than one terminal airspace or used in a procedure common to more than one airport in a single terminal airspace which are not used for en-route Waypoints unique to an aerodrome, with a properly assigned 4-letter location indicator, used for terminal airspace procedures (includes waypoints designated by the ATS provider as requiring prominent display or as having the function of an activation point) En-route environment Terminal airspace procedures and transition to en-route Terminal airspace procedures and transition from en-route Terminal airspace procedures Terminal airspace procedures 5-letter globally unique pronounceable ICAO name code 5-letter globally unique pronounceable ICAO name code 5-letter globally unique pronounceable ICAO name code 5-letter globally unique pronounceable ICAO name code 5-letter globally unique pronounceable ICAO name code, or 5-digit alphanumeric name code specific to the terminal airspace ATNS/HO/C09/30/02/01 Page 182 of July 2010

183 Waypoint and NAVAID co-ordinates are published in the AIP. Co-ordinates specifically associated with an aerodrome are published in the appropriate aerodrome entry. The following chart symbols (as detailed by ICAO Annex 4) should be used to indicate various waypoint types: Waypoint Description Symbol Fly-by waypoint Fly-over waypoint Fly-by waypoint coincident with significant point (compulsory reporting point) Fly-over waypoint coincident with VOR/DME Fly-by waypoint coincident with NDB 5.12 NAVAID Infrastructure Status Monitoring The NAVAID infrastructure to support radio navigation updating prior to entry into various RNAV/RNP airspace (includes the status of GNSS) should be monitored and maintained and timely warnings of outages should be issued through NOTAM ATS System Monitoring Monitoring of navigation performance is required for two reasons: Demonstrated typical navigation accuracy provides a basis for determining whether the performance of the ensemble of aircraft operating on the RNAV routes meets the required performance; and The lateral route spacing and separation minima necessary for traffic operating on a given route are determined both by the core performance and upon normally rare system failures. Both lateral performance and failures need to be monitored in order to establish the overall system safety and to confirm that the ATS system meets the required target level of safety. Radar observations of each aircraft s proximity to track and altitude are typically noted by ATS facilities and aircraft track-keeping capabilities are analysed. ATNS/HO/C09/30/02/01 Page 183 of July 2010