GBAS Roadmap. Summary. GNSSP.4.IP.yy.2. Global Navigation Satellite System (GNSS) Panel Meeting 4. Montreal, 23 rd April 2 nd May, 2003

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1 GNSSP.4.IP.yy.2 Global Navigation Satellite System (GNSS) Panel Meeting 4 Montreal, 23 rd April 2 nd May, 2003 (Prepared by EUROCONTROL) Summary This Information Paper is a roadmap for the Ground-Based Augmentation System (GBAS) to GPS. It describes the GBAS system and its applications, including those supported by a GBAS positioning service. It identifies the main issues to be addressed in realising these applications and provides a roadmap for future work. The roadmap will be used as an input to European and ICAO work. It will be used to better define ICAO OCP and GNSSP future work programmes and will feed forward into Eurocontrol s GBAS Project work programme. The Panel is invited to consider the paper for its future work programme, further amendments to Annex 10 and incorporation in the preparatory material for the 11 th ANC. The main conclusions and recommendations of a roadmap for the Ground Based Augmentation System (GBAS) to GNSS are summarised in Working Paper XX.

2 EUROPEAN ORGANISATION FOR THE SAFETY OF AIR NAVIGATION EUROCONTROL Draft Edition : 1.0 Edition Date : 25 February 2003 Status : Proposed Issue Class : Restricted EUROPEAN AIR TRAFFIC MANAGEMENT PROGRAMME

3 DOCUMENT IDENTIFICATION SHEET DOCUMENT DESCRIPTION Document Title EWP DELIVERABLE REFERENCE NUMBER: PROGRAMME REFERENCE INDEX EDITION : 1.0 EDITION DATE : 25 February 2003 Abstract Keywords GBAS Operational Concept CAT I Roadmap CONTACT PERSON : Eric Perrin TEL : UNIT : GNSS DOCUMENT STATUS AND TYPE STATUS CATEGORY CLASSIFICATION Working Draft o Executive Task o General Public o Draft o Specialist Task o EATMP o Proposed Issue ã Lower Layer Task ã Restricted ã Released Issue o INTERNAL REFERENCE NAME: ELECTRONIC BACKUP

4 DOCUMENT APPROVAL The following table identifies all management authorities that have successively approved the present issue of this document. AUTHORITY NAME AND SIGNATURE DATE Edition: 1.0 Page iii

5 DOCUMENT CHANGE RECORD The following table records the complete history of the successive editions of the present document. EDITION DATE REASON FOR CHANGE SECTIONS AFFECTED September 2002 Eurocontrol review All October 2002 Early draft for distribution to GBAS working All group meeting 5 on 9-10 October December 2002 Eurocontrol review All December 2002 Eurocontrol review All January 2003 GBAS working group review All 0.6 N/A Internal comments added All February 2003 Eurocontrol added All February 2003 Final comments before presentation to ICAO GNSSP/4 All Edition: 1.0 Page iv

6 GLOSSARY AC ACAS AFCS ADS ADS-B AIC APV A-SMGCS ATC CMC DADC DME ECAC EFIS EICAS EGPWS EUROCAE FAA FAS FCU FDIU FG FMC FMS FTP FWC GA GBAS GDPS GLONASS GLS GNLU GNSSP GNSS GPA GPIP GPS IAF ICAO ICD IFR ILS IMC IRS JAA LAAS LNAV LTP MAP Advisory Circular Airborne Collision Avoidance System Automatic Flight Control System Automatic Dependent Surveillance Automatic Dependent Surveillance Broadcast Aeronautical Information Circular Approach With Vertical Guidance Advanced-Surface Movement Guidance and Control Systems Air Traffic Control Central Maintenance Computer Digital Air Data Computer Distance Measuring Equipment European Civil Aviation Conference Electronic Flight Information Systems Engine Indication Crew Alert System Enhanced Ground Proximity Warning System The European Organisation for Civil Aviation Equipment Federal Aviation Administration Final Approach Segment Flight Control Unit Flight Data Interface Management Unit Flight Guidance Flight Management Computer Flight Management System Fictitious Threshold Point Flight Warning Computer General Aviation Ground-Based Augmentation System GNSS Differential Positioning Service Global Navigation And Satellite System GNSS Landing System that encapsulates GBAS and SBAS GNSS Navigation and Landing Unit ICAO GNSS Panel Global Navigation and Satellite System Glide Path Angle Glide Path Intercept Point Global Positioning System Initial Approach Fix International Civil Aviation Organisation Interface Control Definition Instrument Flight Rules Instrument Landing System Instrument Meteorological Conditions Inertial Reference System Joint Aviation Authorities Local Area Augmentation System Lateral Navigation Landing Threshold Point Missed Approach Procedure Edition: 1.0 Page v

7 MCDU MCP MLS MMR MOPS MASPS NAC NIC NOTAM NPA NSE NUC OAS OCP OEM ORD P-RNAV PVT QFE MOC MMR RAIM RMU RMS RNAV RNP RPDS RPI RTCA SARPS SBAS SID SIL SPS SRO STAR TCH TCP TCP TDMA TGL TMA UHF VDB VHF VMC VNAV WG WGS Mode Control and Display Unit Mode Control Panel Microwave Landing System Multi-Mode Receiver Minimum Operational Performance Standards Minimum Aviation System Performance Specification Navigation Accuracy Category Navigation Integrity Category Notice To Air Men Non-Precision Approach Navigation System Error Navigation Uncertainty Category Obstacle Assessment Surfaces Obstacle Clearance Panel Original Equipment Manufacturer Operational Requirements Document Precision RNAV Position, Velocity, Time Atmospheric pressure (Q) at Field Elevation Minimum Obstacle Clearance Multi-Mode Receiver Receiver Autonomous Integrity Monitoring Radio Management Unit Root Mean Square Area Navigation Required Navigation Performance Reference Path Data Selector Reference Path Indicator Radio Technical Commission for Aeronautics Standards And Recommended Practices Satellite-Based Augmentation System Standard Instrument Departure Surveillance Integrity Limit Standard Positioning Service Small and Regional Operator Standard Terminal Arrival Threshold Crossing Height Threshold Crossing Point Trajectory Change Point Time Division Multiple Access Temporary Guidance Leaflet Terminal Area Ultra High Frequency VHF Data Broadcast Very High Frequency Visual Meteorological Conditions Vertical Navigation Working Group World Geodetic System Edition: 1.0 Page vi

8 TABLE OF CONTENTS DOCUMENT IDENTIFICATION SHEET...II DOCUMENT APPROVAL...III DOCUMENT CHANGE RECORD... IV GLOSSARY... V TABLE OF CONTENTS... VII 1 INTRODUCTION General Background Scope Document contents SYSTEM DESCRIPTION Introduction Overview Ground architecture Service volume Airborne architecture (MMR) Airborne architecture (non-mmr) CAT I operation and transition Procedure design issues Aircraft antenna issues Costs and benefits Required stages and timescales of implementation Conclusions Edition: 1.0 Page vii

9 3 CAT II/III PRECISION APPROACH APPLICATIONS Overview Advantages and disadvantages Critical issues to address Required stages and timescales of implementation Costs and benefits Reversion Transition Issues Stakeholder views and conclusions NEAR-TERM GDPS APPLICATIONS Introduction Applications Advantages and disadvantages Critical issues to address Transition issues Stakeholder views and conclusions ADVANCED PROCEDURES Introduction Applications Advantages and disadvantages Critical issues to address Conclusions A-SMGCS AND ADS-B Introduction Applications Advantages and disadvantages Critical issues to address Edition: 1.0 Page viii

10 6.5 Costs and benefits Required stages and timescales of implementation Stakeholder views and conclusions AN EXAMPLE FLIGHT General Before Flight Departure Arrival Initial Approach Segment Intermediate Approach Segment Precision Approach Segment Landing Missed Approach Transition from GLS to ILS Taxi Other Aspects CONCLUSIONS AND RECOMMENDATIONS Introduction Conclusions Recommendations REFERENCES AND BIBLIOGRAPHY References Bibliography A STAGES IN GBAS APPLICATION DEVELOPMENT...48 A.1 Introduction A.2 Concept development Edition: 1.0 Page ix

11 A.3 Standards A.4 Ground and airborne infrastructure A.5 Operational procedures A.6 Pre-operational and certification A.7 Timescales B GBAS INSTRUMENT APPROACH PROCEDURES...56 B.1 Introduction B.2 Obstacle Clearance Surfaces B.3 Obstacle Assessment Surfaces B.4 Procedure Design Constraints B.5 Conclusions Edition: 1.0 Page x

12 1 INTRODUCTION 1.1 General This document is a roadmap for the Ground-Based Augmentation System (GBAS) to GPS. It describes the GBAS system and its applications, including those supported by a GBAS positioning service. It identifies the main issues to be addressed in realising these applications and provides a roadmap for future work The roadmap will be used as an input to European and ICAO work. It will be used to better define ICAO OCP and GNSSP future work programmes and will feed forward into Eurocontrol s GBAS Project work programme. It will also be used by European standards and regulatory institutions to guide their work programmes and it will be reflected in the Eurocontrol navigation action plan [1] The roadmap is being developed in parallel with a GBAS CAT I Concept of Operations. Some issues related to CAT I are discussed in that document and therefore not covered in great detail here. 1.2 Background The validation of the SARPs 1 developed to support GBAS-based CAT-I operations was completed in June 2000 at the Seattle meeting of the ICAO GNSS Panel and the SARPs became applicable in November However, and in line with a motion set within the RTCA SC-159 WG4 Authors Group that revisited the LAAS MOPS (DO-253) and ICD (DO-246A), the GNSSP WG-B PVT (Position Velocity & Time) Subgroup decided at the Banff meeting of the GNSSP to implement SARPs changes to enable the use of PVT for area navigation (RNAV) using the GBAS signal-in-space Since March 2001, ICAO calls PVT, when augmented by GBAS, the GDPS (GNSS Differential Positioning Service) Given the new potential operations supported by GBAS, the Eurocontrol GBAS Working Group agreed in October 2001 on the need for an Operational Concept for GBAS as a matter of urgency. This led to a presentation to the GNSSP Working Group A/B meeting in Rio de Janeiro (Brazil) on 22 Oct Nov a working paper [2] that recommended that: GNSSP WG-A should, in close co-operation with OCP and the end users, describe the mapping of an operational concept, the required steps, and both requirements and a timeline for operational implementation. Emphasis should be placed on the minimisation of the need for re-investment in terms of: a). Installation; b). Certification; and c). Operational approval and safety assessment. This document results from that decision and it identifies in particular applications that will complement GBAS CAT-1, i.e. operations that could bring benefits at 1 GLONASS requirements will be included at a later date in the ICAO GNSS SARPs. Amendment 77 to ICAO GNSS SARPs also covers additional ranging sources from SBAS geostationary satellites. Edition: 1.0 Page 1

13 1.3 Scope small marginal cost over a CAT-1 ground/airborne installation in line with items a). to c). above mentioned This document considers all applications of GBAS, including precision approach and applications of the GBAS positioning service. It describes the application of CAT I precision approach, which is currently under development, and then considers the following additional and longer term applications: Precision approach: CAT II and CAT III. Near-term GDPS applications: SIDs, STARs, non precision approach, APV1, APV2 and missed approach procedures. Advanced procedures: Curved approaches and independent parallel runway operation. A-SMGCS and ADS-B: A-SMGCS navigation and guidance and ADS-B surveillance For each application, the advantages, disadvantages, critical issues, benefits and costs are discussed. For applications of most interest, a description of stages of development and timescales are also given. 1.4 Document contents Section 2 describes the GBAS system and operation, focussing on its use for CAT I precision approach Other applications of GBAS are described in the following sections: CAT II/III precision approach applications in Section 3, Near-term GDPS applications in Section 4, Advanced procedures in Section 5, A-SMGCS and ADS-B in Section Section 7 includes a description of an example flight Recommendations are given in Section 8 and references in Section Annex A describes the necessary stages in development of GBAS application Annex B describes the requirements for GBAS instrument approach procedures. Edition: 1.0 Page 2

14 2 SYSTEM DESCRIPTION 2.1 Introduction This section describes the GBAS system and some CAT I implementation issues, including transition and procedure design. An example of the operational use of GBAS for CAT I precision approach is given in Section Overview The Ground Based Augmentation System (GBAS) is a safety-critical system consisting of the hardware and software that augments the GPS Standard Positioning Service (SPS) and provides enhanced levels of service supporting all phases of approach, landing, departure and surface operations within its area of coverage. GBAS will initially be applied solely to the approach phase of flight as an alternative to ILS CAT I The GBAS system is part of the Global Navigation Satellite System (GNSS). The GNSS is a world-wide navigation system of satellites. The GBAS system provides augmentation to the GNSS positioning systems under the auspices of the ICAO SARPS (Annex 10) for GPS and GLONASS As an augmentation system, the GBAS system may be divided into three distinct parts: The satellite sub-system (GPS constellation), which provides both the aircraft GBAS receiver and GBAS ground station with ranging information. The satellite signals received by the GNSS receivers are subject to various error sources including atmospheric effects and multipath reflections. The ground station sub-system, which uses two or more GNSS reference receivers. They each calculate pseudoranges for all satellites within view and the ground station calculates differential corrections for each pseudorange, based on its surveyed reference receiver positions. The ground sub-system also monitors the quality and integrity of the ranging signals using the redundant measurements and signal processing techniques. GBAS uses a VHF Data Broadcast (VDB) in the band 108 to MHz. The lowest assignable frequency is MHz and the highest assignable frequency is MHz. The separation between assignable frequencies (channel spacing) is 25 khz. The transmitter broadcasts pseudorange corrections, integrity parameters, and various locally relevant data such as atmospheric model and Final Approach Segment (FAS) data that are referenced to the World Geodetic System (WGS 84) co-ordinate system, defining the path in space to enable the precision approach operations. When it uses an antenna with an omnidirectional pattern, the ground station has the capability to support multiple runway end approaches. Consequently, the broadcast includes various approach segments (FAS) which consist of Path Points describing approaches for each related runway, the FAS Vertical Alert Limit/ Approach Status, and the FAS Lateral Alert Limit/ Approach Status. The aircraft sub-system tunes to the correct frequency using a channel number consisting of five numeric characters. The channel number enables the airborne sub-system to select the Final Approach Segment (FAS) data block that defines the correct approach. The correct FAS data block is se- Edition: 1.0 Page 3

15 lected by the Reference Path Data Selector (RPDS) which is included as part of the FAS definition data in one of the broadcast message. The aircraft subsystem also uses the VDB transmission to correct its own measurements using the corrections and related data in the broadcast. This data is further processed to calculate a position with improved accuracy at the required level of integrity. The aircraft sub-system uses the differentially corrected aircraft position, integrity information and the FAS data to supply navigation guidance signals (vertical and lateral deviations, distance to threshold crossing point, and validity flag) to the pilot s display and to the autopilot The GBAS system is shown in Figure 1. GNSS Satellites GNSS Signals and Navigation Messages VHF Data Broadcast GBAS Ground Subsystem Figure 1: The GBAS System Future applications might require additional infrastructure components, such as pseudolites, combined GPS/GALILEO constellations or additional GPS frequencies, but these are not necessary for CAT I operations. 2.3 Ground architecture The GBAS ground subsystem consists of two or more GNSS receivers, the GBAS housing unit containing ground processing functionality, data broadcast functionality and integrity monitoring functionality, and one or more VDB antenna to transmit ranging corrections and other information to the aircraft The general architecture of a CAT I GBAS ground subsystem is illustrated in the following diagram. Edition: 1.0 Page 4

16 Shelter VDBs Datalink Datalink processing, Datalink processing, transmitter Datalink processing, transmitter and processing, transmitter receiver and transmitter receiver and receiver and receiver Correction Correction and and message message processing xrocessinx Low noise Low noise amplifier Low noise amplifier and ranging Low noise amplifier and ranging receiver amplifier and ranging receiver and ranging receiver receiver GPS Rxs Maintenance Uninterruptible power supply Remote status and control units Minimum system shown in solid lines. Each VDB and GPS receiver may be single thread or redundant. The ground station sub-system uses two or more GNSS reference receivers and can make use of additional antenna systems, sited to provide signal path diversity such that collectively they meet the coverage requirements. Additional VDB antennas may be used to meet coverage requirements, and additional receiver antennas will be used for integrity monitoring. Redundancy of internal modules will vary according to manufacturer implementation and local requirements. Figure 2: The GBAS ground system The internal ground functions performed by the GBAS subsystem include: GNSS reference receiver function, which receives, tracks and decodes the GNSS Satellite Signals in space and measures pseudorange to, and range rates for, each GNSS satellite in view. Reference processing function, which calculates pseudo-range correction and integrity data for each valid satellite in view, by reference to the reference receiver s antenna positions. VHF data broadcast (VDB) transmit function, which transmits the messages to all the aircraft within the coverage area through the VDB antenna. Integrity monitoring function, which validates all messages being provided to the VDB function, and all messages actually transmitted. GNSS ranging source monitoring function, which monitors the GNSS signals to detect conditions that will result in improper operation of differential processing. Local and remote control and status functions, which provides basic operational control and status functions. Operation and maintenance functions, which provides field download functions, and supports fault isolations and maintenance actions. Power supply functions, which provides power to all ground subsystem units The location of the GNSS and VDB antennas is determined from the layout of the aerodrome, buildings and other obstructions within the operational plan. EURO- CAE MOPS, presently being defined for the GBAS ground station, defines siting requirements that accompany National Government Aviation Authority regulations, industry practices and local building regulations as well as obstacle limitation requirements of ICAO Annex 14 and other relevant national guidelines. Edition: 1.0 Page 5

17 2.3.5 In addition to the MOPS, it has been suggested by European Stakeholders that it would be beneficial to produce general (ie not vendor-specific) guidelines on siting criteria. 2.4 Service volume Each GBAS approach has a service volume that is defined as the region within which the system meets the accuracy, integrity and continuity requirements The minimum service volume to support CAT-I precision approach operations as defined in the ICAO SARPs is: Laterally: beginning at 137 m (450 ft) each side of the Landing Threshold Point/Fictitious Threshold Point (LTP/FTP) and projecting out ±35 degrees either side of the final approach path to 28 km (15 NM) and ±10 degrees either side of the final approach path to 37 km (20 NM); Vertically: within the lateral region, up to the greater of 7 or 1.75 times the promulgated glide path angle (GPA) above the horizontal with an origin at the Glide Path Intercept Point (GPIP) and 0.45 GPA above the horizontal or to such lower angle, down 0.30 GPA, as required to safeguard the promulgated glide path intercept procedure. This coverage applies between 30 m (100 ft) and 3000 m ( ft) HAT This volume is depicted in the figure below. (Note that minimum ranges may be promulgated differently per facility.) Figure 3: GBAS CAT I service volume Edition: 1.0 Page 6

18 2.4.4 The coverage required to support the GBAS positioning service is dependent upon the specific operations intended. The limit on the use of the GBAS positioning service information is given by the Maximum Use Distance (D max ), which defines the range within which the required integrity is assured and differential corrections can be used for either the positioning service or precision approach In addition, to support future applications such as autoland, GBAS coverage should be extended to the runway surface. The requirements for coverage on the runway are not yet defined and the proposed minimum altitude of 3.7 m requires validation and further work. 2.5 Airborne architecture (MMR) The main functions of the GBAS airborne subsystem are essentially: A GNSS Receiver Function that receives, tracks, and decodes the GNSS satellite signals; A VDB Receiver Function that receives and decodes the messages broadcast by the GBAS ground subsystem; A Navigation Processing Function that receives the measurement of the pseudoranges from the GNSS receiver function, applies the differential corrections received from the VDB receiver function and calculates the differentially corrected aircraft position. The navigation processing function extracts from the various FAS path construction data blocks received on the frequency the one having the matching Reference Path Data Selector (RPDS) Many large aircraft are equipped with a multi-mode receiver (MMR) which will support the integration of GBAS. Figure 4 illustrates a typical MMR architecture. FMS MCDU Database Ref trajectory Pos determination Nav guidance to AFCS (LNAV, VNAV, Speed) GPS & SBAS MMR L-Band VHF UHF Position output to FMS GNSS GLS deviations VDB ILS Loc/GS Other nav sources Localiser/ Glideslope Deviations Deviations output to AFCS (Approach/ land functions) C-Band MLS az/el xls tuning Figure 4: A GBAS MMR airborne architecture Figure 5 illustrates the interrelationship between an MMR, Flight Management System (FMS) and Automatic Flight Control Systems (AFCS). Note that in Figure 5 the position outputs for navigation purposes are either GPS standalone position with integrity provided by RAIM, or GBAS or SBAS differentially-corrected position with associated horizontal protection level. Note that redundancy of FMS, MMR, AFCS and other systems is not shown. Edition: 1.0 Page 7

19 MMR GPS with RAIM, GBAS or SBAS output ILS look-alike deviations FMS LNAV, VNAV and speed guidance AFCS IRS DME VOR DADC etc Approach/land functions (Capture switching controls transition from FMS guidance to MMR guidance) Figure 5: Interconnection of MMR, FMS and AFCS Integration of GBAS into an MMR-equipped aircraft is likely to require a modification to several on-board systems, although some of the changes may have been provisioned already on the aircraft. Most changes related to peripheral units are for software changes only. Table 1 lists the systems likely to require change on an MMR equipped aircraft. Note that the names for different systems vary between manufacturers. Edition: 1.0 Page 8

20 System MMR FMC AFCS Multi-functional Control and Display Unit (MCDU) Mode control Panel (MCP, FCU) Radio Management Unit (RMU) Electronic Flight Information Systems (EFIS) Monitoring and alerting systems (EICAS, EICAM) Central Maintenance Computer (CMC, FDIU) Reason for change Addition of GBAS software changes depending on MOPS; physical aircraft installation (possibly including antenna provisions). Database changes to allow approaches to be identified as GLS and to include GLS channel numbering. Housekeeping systems will need to be changed, e.g. preautoland availability tests. (Flight control laws not changed) Any pages offering precision approach selection, or precision approach data and navigation sensor information, testing and statues may be affected, and new pages may be required. Change to allow pilot to select GLS 2. (This function may have been provisioned). Changes to allow GLS approaches to be selected. Indication to pilot of GLS approach. (This function may have been provisioned) Changes because systems under monitor have been changed. Changes because systems under maintenance have been changed. Table 1: Aircraft systems that may require change Figure 6 shows a typical GBAS CAT I MMR aircraft architecture for an Airbus aircraft. 2 For either manual or automatic selection, when the approach has been activated, the equipment will display the four character Reference Path Identifier (RPI), allowing the pilot to confirm that the selected procedure agrees with the desired procedure published on the approach plate. Additionally, the display of the RPI indicates the correct VDB transmission is being received and valid messages are being processed for the selected approach. 3 Some MMR-equipped aircraft may have been already provisioned for all precision approach systems. Edition: 1.0 Page 9

21 GPS Loc/Glide GPS MMR1 MMR2 FCU (Flight Control Unit) FG FG (Flight Guidance) FG FMS (Flight Management System) FG RMP (Radio Management Panel) DMC (Display Management Computer) FG ACP (Audio Control Panel) FG FWC (Flight Warning Computer) FG FDIU Flight Data Interface Management Unit) Figure 6: Typical Airbus aircraft architecture Critical issues in the illustrated architecture and design are: The MMR generates a GNSS positioning signal using RAIM, SBAS or GBAS. The accuracy and protection level of the output depends on the augmentation used. The position is output to the FMS, EGPWS, etc and, if GBAS is available, also used in the MMR to derive the deviations for approach. Navigation function provided by the MMR shall comply with the following conditions: When the MMR outputs a non-corrected position, the navigation function shall comply with the performance requirements defined in ED-72A. In this case the protection level will be the RAIM integrity limit. When the MMR outputs a SBAS corrected position, the navigation function shall comply with the performance requirements defined in DO-229C. In this case the protection level shall be WAAS defined HPL for navigation outputs. (Only HPL is provided and not VPL.) When the MMR outputs a GBAS corrected position, the navigation function shall comply with the requirements defined in DO-253A. In this case the protection level shall be GBAS defined HPL navigation outputs, HPL only being provided. (Only HPL is provided and not VPL.) The GBAS card in the MMR would usually replace any other GNSS receiver. Hence any GNSS position can only come from the MMR. The MMR identifies the active mode (MLS, ILS or GLS) on the ILS look-alike bus. However, it is not known at the time of writing whether the FMS has access to, or uses, this information, or whether the FMS knows the type of augmentation being used for the positioning output. (The source of augmentation would be required to enable GBAS GDPS procedures, as discussed in Section 5.) The autoflight computer is driven by the FMS in automatic flight (LNAV, VNAV and thrust modes) and by the MMR during approach and landing. There is a transition ( capture ) between the two modes that is controlled by the AFCS. Edition: 1.0 Page 10

22 Associated with multiple approach/landing guidance sources from the MMR (ILS, MLS and GLS), changes will be required to some of the AFCS "household" functions, including sensor and torque voting algorithms, fault detection, pre-autoland availability tests, mode and sub-mode switching, reconfiguration and degradation switching and mode annunciation. The FMS holds the database for tuning the GBAS (or ILS or MLS). The actual tuning can be performed by the FMS or manually. In the latter case, some FMS cross-checks the manually-tuned value. Either way, the FMS database and MCDU changes must be able to support approach guidance additional to ILS. The FAS received from the ground station could be output from the MMR to the FMS on a special bus. No information is given in the MMR s interface control document (ICD) as to when after acquisition the information is provided. The FMS could use this information to make a consistency check with the FMS database. 2.6 Airborne architecture (non-mmr) Non-MMR architectures are expected to provide the same GBAS functionality as MMR architectures. Non-MMR architectures are more common on smaller and older aircraft Aircraft fitted with non-mmr architectures include many aircraft used by private individuals and companies for social and commercial purposes, including air taxi and corporate travel; e.g. Pilatus PC-12, Cessna Caravan, Citation I/II and Raytheon King Air. It also includes aircraft that are classified by ICAO as light aircraft according to wake vortex category, amounting to a total of approximately 5000 aircraft within ECAC airspace The integration of GBAS into non-mmr aircraft will vary greatly with the complexity of the avionics suite. The GBAS solution for light IFR aircraft, currently equipped with an ILS receiver, may be, as for ILS, a simple standalone receiver and display supporting manually-flown CAT I approaches Increasing avionics complexity in non-digital aircraft is leading to a more modular integration, for example with the GNSS Navigation and Landing Unit (GNLU) ARINC 756. This is expected to be installed into higher end business jets, such as Falcons, Bombardiers and Challengers. To date, no non-mmr solutions are available to GA. Figure 4 illustrates the architecture of a GNLU and the interfaces with other systems. 4 Aircraft population figures derived from information from Eurocontrol based on 2000 population data. 5 Examples of such low-end avionics for ILS systems include the NARCO NAV 122-D and Garmin GNS 430/530 solutions. Edition: 1.0 Page 11

23 Flap Pos. Instr. Clock DME IRS/Att ADC Ext PADB APM Dataloader (615A) Fuel Flow/Qty 2 \ 3 \ 2 \ Approach Control Panel Ext GNSSU NDB (424) Navigation Function (702) 2 \ Dedicated Annunciators/ Alerts MCDU (739) GNSS Top Ant (opt) LOC/VOR Ant GS Ant (opt) MLS Omni & Landing Ant s (opt) Ext LAAS D/L Ext ILS/MLS \ 2 GNSS Receiver (743) GBAS D/L VHF RF GS RF MLS RF Corr, Path PADB ILS/VOR Function (710/547) MLS Function Dev Dev GNLU GLS Approach Navigator (755) Dev ILS/MLS/GLS Switch Dev I/O 2 \ 2 \ ATC, ADS \ 4 ADS-B Dev, Str, Map Dev, Str, Sel Alt CMU or MU Primary Displays Flight Director/ Autopilot Printer 743 Outputs ACAS OMS/ CFDS = Optional Figure 7: GNLU functional block diagram It should be noted however, that integration of a GNLU type solution might not be possible into integrated avionics suites as currently advertised by OEMs such as Cessna. This is because the OEM avionics interfaces do not always conform to the GNLU specification (ARINC 756) The application of P-RNAV and RNP RNAV navigation standards will also lead to an increased dependence upon navigation computers and FMS. This is currently illustrated as some small jets are being fitted with navigation computers that are interfaced to flight directors, GPWS, ACAS II, etc. In this environment, the application of an integrated GNLU solution will be increasingly common. 2.7 CAT I operation and transition The GBAS airborne equipment provides proportional guidance for lateral course deviation and vertical path deviation for a straight-in approach. It also computes the distance from the measured position of the aircraft to the runway Threshold Crossing Point (TCP) for display to the pilot. The TCP is a point at a height defined by the Threshold Crossing Height (TCH) above the Landing Threshold Point (LTP) or Fictitious Threshold Point (FTP) Figure 8 shows the transition to precision approach (ILS/MLS/GLS). The intercept track may be RNAV generated or a radar vector. It is normally a track to the Initial Approach Fix (IAF) and is optimally a 30 intercept angle in level flight [Ref 3, Edition: 1.0 Page 12

24 Chapter 21.2 and Table 21-1]. Note that the IAF for GBAS may be different from the IAF for an ILS serving the same runway. Limit of proportional guidance Centreline Runway Limit of proportional guidance Intercept track Figure 8: Join to precision approach As the aircraft is flying the intercept track, guidance is LNAV/VNAV derived from RNAV/FMS. The AFCS/autopilot approach mode is armed. As the aircraft enters the GBAS proportional guidance sector, the GBAS localiser is captured, and lateral steer is derived from GBAS, the RNAV/FMS LNAV information being discarded once GBAS localiser is captured As with ILS, the precision approach intercept still requires the aircraft to maintain a constant altitude after localiser intercept until glidepath capture The RNAV/FMS generated intercept track to the IAF is not so critical, provided that the aircraft enters the GBAS proportional guidance sector prior to reaching the RNAV/FMS IAF. The GBAS proportional guidance sector width at a range of 10 NM is at least 3000 /0.5NM. This increases to 6000 /1NM at a range of 20NM Sensitivity on the display indicator, for both lateral and vertical deviations, increases during the final approach due to the emulation of an angular convergence of the localizer and glide slope origins, with an optimal full-scale deflection angle of 2 degrees (localiser) and 0.36 degrees (glideslope) During any phase of the approach, if the GBAS service degrades to the level where the system can no longer provide guidance with the required level of safety, the pilot is alerted that the guidance is invalid consistent with the current presentations of the particular instrument display. In the event that the GBAS service degrades such that the vertical guidance no longer provides precision approach performance and the aircraft is established on the approach glidepath, then the aircraft will execute a missed approach The AFCS treats ILS and GBAS as the same for the purpose of precision approach. For both systems, the guidance is only available when the aircraft is within the system proportional guidance sector Note that GBAS could also support compound vertical profiles. Some airports have glidepath angles in excess of 3 for either obstacle or environmental reasons although current AFCS are only certified for autoland at up to 3.1. With the current system architecture, a compound vertical profile should be possible, allowing, for instance, an initial descent in the precision segment at 4, reducing to 3 by 1NM from threshold. Edition: 1.0 Page 13

25 2.8 Procedure design issues In November 2003, ICAO will circulate to States for comment a draft chapter of Pans-Ops (Doc 8168) concerning GBS CAT I approaches. The guidance material is expected to be published in November The GBAS guidance material will be based on ILS instrument approach criteria (Chapter 21), on the assumption that GBAS will meet or exceed ILS accuracy. In fact, GLS is likely to exceed ILS criteria (since some GBAS errors are linear, whereas all ILS errors are angular) and therefore there may be scope for changing the OAS criteria for GBAS to enable lower obstacle clearance altitudes/heights The ICAO ILS collision risk model has not yet been validated for GBAS, although some work has been carried out towards this objective. Re-validating the model for GBAS is not a priority for CAT I use It is the intention of ICAO to address Cat II/III GBAS operations in Annex B gives more detail on the criteria for GBAS instrument approach design and the procedure design issues associated with GBAS. 2.9 Aircraft antenna issues This section discusses aircraft antenna issues for GBAS. These issues apply to all applications considered here, not just CAT I The localiser aerial on medium/large aircraft is normally located within the nose radome structure, and is therefore by design forward-looking, and is somewhat insensitive to signals from the side and rear of the aircraft. This antenna is automatically selected by the action of tuning an ILS frequency. For other frequencies in the band 108MHz 117.9MHz, an omni-directional aerial will be automatically selected. The use of forward-looking aerials on an aircraft could have a significant impact on GBAS operations, ie: For precision approach applications: The GBAS signal may not be acquired until the aircraft has started to turn towards the VDB signal. It is expected the aircraft would have to be within about 30 degrees of the centerline. For terminal airspace applications: There may be difficulties implementing GBAS-augmented GDPS unless omni-directional aircraft antennas can be used. For surface applications, such as A-SMGCS and ADS-B: Again there may be difficulties implementing GBAS-augmented GDPS unless omni-directional aircraft antennas can be used. For guided roll-out: It may be necessary to place the VDB antenna at the end of the runway. A separate VDB antenna would therefore be required at each CAT II/III runway end It is possible that the high output power of the VDB (150W) will allow either forward-looking localiser or omni-directional VOR antennas to be use on the aircraft. However, this could raise technical issues as the localiser antennas may have unspecified gain in non-forward or backward looking directions. (RTCA MOPS for localiser equipment (DO-195) specify antenna gain in forward and backward directions, but not other ones.) Edition: 1.0 Page 14

26 2.9.4 There will be further aircraft antenna issues if the VDB coverage volume increases, eg for terminal airspace applications. Signal strength at the edge of the VDB coverage volume would have to be confirmed and it may be necessary to use omni-directional aircraft antennas. Signal strength at the edge of coverage would also need to be validated through flight checking Costs and benefits Costs (ground) Table 2 contains generic estimates of the cost of a GBAS CAT I ground station [5]. These costs are only indicative (not dependent on the manufacturer) and individual costs will depend on local factors as well as commercial negotiations. Configuration Minimum CAT I system 3 GPS receivers 2 Processing chains 1 VDB transmitter/monitor Equipment and installation 313, ,000 High availability CAT I system 4 GPS receivers 3 Processing chains 2 VDB transmitters/monitors Site commissioning (procedure design and flight inspection) 30,000 30,000 Total 343, ,000 Table 2: Indicative CAT I GBAS ground station costs An aerodrome introducing GBAS CAT I procedures will incur additional costs, not just the system costs of the GBAS system. The additional costs may include: Lighting: An aerodrome being upgraded to CAT I criteria may require additional lighting. The requirements of Annex 14 and additional national certification and licensing authorities may require the installation and maintenance of further approach lights and lighting patterns. Costs associated with the installation of light patterns will vary according to aerodrome size and intended operational capability. It is envisaged that since the initial intention is for GBAS to operate as an ILS look-a-like service that the same lighting requirements will exist for GBAS CAT I operations. Note: The requirements for precision approach lighting under CAT 1 operating conditions are presented in Annex 14 sections through Runway markings: Current runway and taxiway markings are required to indicate exclusion zones and holding areas for ILS critical areas. Signs: An aerodrome upgrading to CAT I rating will require additional signposts according to the requirements of Annex 14 and additional national regulatory and certification bodies. Signs are required to indicate direction to, holding areas of and other markings related to taxiways and runways of CAT I capabilities. Flight inspections: Flight inspection requirements for ILS are defined in ICAO Doc This document does not give recommendations on the periodicity Edition: 1.0 Page 15

27 of flight checks and they vary considerably between States. ILS CAT I flight checks generally occur at periodicity of between 90 days to 18 months. GBAS should require fewer flight inspections, and indeed should not require any regular GBAS flight checks. Both GBAS and ILS will require flight inspections when a procedure is first implemented and then following any changes to it. In the case of GBAS, this will include after any database changes. Procedure Design: GBAS CAT I approach procedures will need to be designed. These will be very similar to ILS CAT I procedures. Fire fighting: There are no specific requirements for fire fighting capabilities due to CAT I. The requirements for rescue and fire fighting services are based upon the operational capacity of the aerodrome and size of operational aircraft. The installation of GBAS enabling CAT I operations could enable further operations at the aerodrome. The expansion of operations may enable or require larger aircraft to utilise the aerodrome, requiring an expansion of the fire fighting capabilities. The expansion of fire fighting capabilities may be either through additional fire fighting vehicles or the upgrade and replacement of existing vehicles. This cost is not necessarily directly due to GBAS as aerodromes will install CAT I capabilities to attract additional flights and may already have the necessary level of rescue and fire fighting capabilities The following table estimates the costs that may be expected from a minimum GBAS installation, compared to an ILS. It can be seen that GBAS has expected lower lifetime costs than ILS. Since one GBAS can support multiple runway ends, greater savings will be achievable at some airports. In fact, there are many airports that have invested in ILS which serves only one runway end. With GBAS, all runway ends could be served with a single system. The additional cost would be the instrument approach procedure design for other runway ends, at a cost of circa SHUSURFHGXUH Component ILS GBAS Source/Comments Ground station 471, ,000 Refs [5], [17], [18] Installation 236,000 30,000 Refs [5], [17], [18] Lighting (per runway end) 471, ,000 Refs [5], [17], [18] Fire service - - Runway markings Signs No indicative figures obtained No indicative figures obtained Flight inspection 134,000 25,000 Refs [19] Figure is total over 15yrs, discounted at 8%. Procedure design 20,000 20,000 Ref [5] Total 1,332, ,000 Table 3: Total indicative ILS/GBAS ground costs Note that no cost has been included for fire service. As noted, the installation of GBAS enabling CAT I operations could enable further operations at the aerodrome. This cost is not due to GBAS as aerodromes will install CAT I capabilities Edition: 1.0 Page 16

28 to attract additional flights and may already have the necessary level of rescue and fire fighting capabilities due to the types of aircraft already handled Costs (MMR aircraft) The installation of an GBAS MMR architecture will require changes to other onboard systems. Most changes are expected to be of software only The following table presents a cost estimation for the installation of GBAS into an MMR certified aircraft. Note that the cost of down-time, which may be significant, is not shown. Cost Component MMR Source\Comments MMR TBD TBD FMC Modifications TBD TBD MCP TBD TBD EFIS TBD TBD MCDU TBD TBD AFCS TBD TBD CMC TBD TBD EICAS Interface TBD TBD Installation TBD TBD STC/SB TBD TBD Certification TBD TBD Training TBD TBD Antenna (x2) TBD TBD Database TBD TBD TOTAL TBD TBD Table 4: Indicative aircraft costs (MMR ) Costs (non-mmr aircraft) The following table presents a cost estimation for the installation of GBAS into a non-mmr certified aircraft. Edition: 1.0 Page 17

29 Cost Component Standalone GNLU Source\Comments Purchase TBD TBD TBD Installation TBD TBD TBD STC/SB TBD TBD TBD Certification TBD TBD TBD Training TBD TBD TBD Antenna (x2) TBD TBD TBD Database TBD TBD TBD TOTAL TBD TBD TBD Table 5: Indicative aircraft costs (non-mmr) Benefits GBAS CAT I precision approach may bring the following benefits: GBAS will enable multiple approaches at the same runway to be introduced more easily. Examples of this are offset thresholds and steeper slopes for lighter aircraft (possibly enabling reduced runway occupancy time and wake separation). This could be a significant benefit, and further work is suggested to investigate its magnitude. Provision of arrival, approach and departure guidance can be provided for different aircraft types independently. For example, helicopters operations can become independent from fixed wing operations, which could help increase helicopter flow rates in CAT I conditions at airports where mixed modes apply. Airports that cannot install ILS, e.g. due to terrain or real estate constraints, may be able to introduce a precision approach capability. Various solutions, such as offset localisers, are available that at least partially overcome these difficulties. There are only a small number of these airports that cannot install ILS. Two examples are Sumburgh 09/27 and Isle of Man 08, where realestate constraints force the use of (uncategorised) offset localiser ILS approaches. GBAS would allow in-line CATI to be realised at these locations. GBAS has a more stable signal than ILS, and there is less interference with preceding aircraft. Also, it does not suffer localiser or glide path bend. This will be a more significant benefit for CAT II/III than CAT I. GBAS VDB signals will be less sensitive than ILS to reflections and multipath from buildings and obstacles. So GBAS should be less of a constraint to the construction of new airport buildings. This benefit is very airport specific. GBAS provides a continuous indication of range to the Datum Crossing Point (DCP) during final approach. Due to GBAS system requirements on Navigation System Error (NSE) and data latency, the accuracy of the distance to threshold output will be significantly better than the ICAO 0.20 NM requirement on DME-based distance. GBAS will not require any VHF Marker or DME infrastructure to perform the ranging measurement, which would result in a cost saving. It will also avoid the need for pilot selection of DME channel where this is not associated to an ILS by frequency pairing. Edition: 1.0 Page 18

30 GBAS will ease frequency allocation because it will not be so constrained by frequency association as ILS. In particular it will not have the frequency associations of ILS with VOR/DME/MLS. This will also release additional DME channels for use. GBAS will have reduced VHF frequency requirements compared to ILS, i.e. fewer frequencies will be required to support the same number of precision approaches. This is because the separation between assignable frequencies is 25 khz, a TDMA technique is used to allow multiple GS to operate on the same frequency and multiple runway ends can be covered by a single GS. Aircraft capturing a localiser signal outside of the proportional guidance region (ie >17 NM from the localiser antenna) may prematurely initiate a turn onto the localiser centreline. This is referred to as false capture that is most likely to occur 8 10 degrees from the localiser centreline, which is an area of high modulation of the localiser signal. The result is that the pilot prematurely changes HDG or LNAV mode to APP. This problem does not exist with GBAS Required stages and timescales of implementation Annex A identifies the generic actions required to implement a GBAS application. Figure 9 shows timescales for development of GBAS CAT I in terms of these actions. GBAS CAT I should be operational from early The timescales shown, and the order of tasks, will vary according to the actual implementation of a particular application. For CAT I, the timescales have been adjusted to match those of on-going and planned activities. Shaded actions in Figure 9 are complete. Edition: 1.0 Page 19

31 Notes Line 5 There is no generic business case for GBAS CAT I in Europe.. Line 6 European transition is presently being undertaken locally by States Line 15 PANS-OPS CAT I criteria are still draft Figure 9: Timeline for the development of GBAS CAT I 2.12 Conclusions The development of GBAS CAT I is well underway and will be completed in the next few years. There is an opportunity to maximise the benefits from CAT I, and the following actions have been identified: Review obstacle clearance criteria for GBAS CAT I, potentially leading to reduce OCA/H for GBAS CAT I compared to ILS CAT I. Work has already started in this area in Germany. Investigate the benefits of multiple approaches at the same runway. Examples of this are offset thresholds and steeper glideslopes for lighter aircraft (possibly enabling reduced runway occupancy time and wake separation). Investigate the benefits of provision of arrival, approach and departure guidance for mixed aircraft operations. This should allow improved capacity management where, for example, there are mixed helicopter and fixed wing operations Finally, it has been suggested that production of European guidelines on GBAS siting criteria would be beneficial. Edition: 1.0 Page 20