EE Chapter 14 Communication and Navigation Systems

Transcription

1 EE Chapter 14 Communication and Navigation Systems Two way radio communication with air traffic controllers and tower operators is necessary. Aviation electronics or avionics: Avionic systems cover many controlling systems in an aircraft such as communication radio, navigation systems, weather detection systems and flight management systems. All modern avionic systems conform to Aeronautical Radio Incorporated (ARINC) standards. ARINC is a corporation established by foreign and domestic airlines, aircraft manufacturers and transport companies to set standards for aircraft systems. ARINC was incorporated in 1929 as Aeronautical Radio, Incorporated. It was chartered by the Federal Radio Commission (which later became the Federal Communications Commission) in order to serve as the airline industry s single licensee and coordinator of radio communication outside of the government. ARINC is a major provider of transport communications and systems engineering solutions for eight industries: aviation, airports, defense, government, healthcare, networks, security, and transportation. ARINC 500 and 700 standards for communication, navigation and identification systems: The 500 Series describes analog avionics equipment used on aircraft such as the Boeing 727, Douglas DC 9, DC 10, Boeing 737 and 747, and Airbus A300. ARINC 573 is a standard format for data parameters recorded by digital flight data recorder and flight data recorder required by the FAA and ICAO. The 700 Series describes digital systems and equipment installed on aircraft of digital avionics systems, including data link protocols.[6] ARINC 708 is the standard for airborne weather radar. It defines the airborne weather radar characteristics for civil and military aircraft. This standard also defines the way to control and get information from the radar. ARINC 717 Flight Data Recorder for Commercial Aircraft ARINC 739 is the standard for communication between the MCDU and the systems attached to it. ARINC 741 is the standard for a first generation L band satellite data unit. ARINC 746 is the standard for a cabin telecommunications unit, based on Q.931 and CEPT E1. ARINC 761 is the standard for a second generation L band satellite data unit, also called Swift64 by operator Inmarsat. ARINC 763 is the standard for a generic avionics file server and wireless access points. ARINC 781 is the standard for a third generation L band satellite data unit, also called SwiftBroadband by operator Inmarsat. ARINC 791 is the in work standard for a Ku band satellite data unit. 1

2 Communications Radio communication systems for aircraft are primarily for the purpose of air traffic control, however, commercial aircraft also utilize a range of high frequencies for communicating with ground stations and other aircraft. Communications for air traffic control are in the VHF band ( MHz range). High frequency communication systems Operating frequency range 2 to 30 MHz. HF communication systems are used for long distance radio transmissions to provide two way voice communication with ground stations or other aircraft. Antenna tuning for all transmission frequencies is accomplished automatically by means of an antenna coupler system. HF communication systems are not employed on all aircraft. VHF communication systems VHF communication systems are employed largely for controlling air traffic. The advantage is that the signals are not often distorted or rendered by static and other types of interference. 2

3 Antenna locations for communications and navigation equipment: Digital air/ground Communications services (AIRCOM) in Europe and Australia and ARINC Communication Addressing and Reporting System (ACARS) in US are systems designed to reduce the amount of voice communication on the increasingly crowded communications frequencies. Federal Communication Commission (FCC, is a government agency to control all electromagnetic emissions in USA and also issue licenses. Satellite Communication (SATCOM) equipment is typically found on aircraft that make intercontinental flights. Common HF communication radios will transmit long distance, however, they are susceptible to interference. SATCOM equipment utilizes frequencies that are relatively static free but normally limited to line of sight distances. SATCOM system consists of three subsystems: the ground earth station, the aircraft earth station and the satellite system. See Fig (pp.301) The satellites act as a relay station for various SATCOM signals. The satellites receive and transmit in L band frequencies (e.g MHz) when communicating with aircraft and in C band frequencies (e.g. 4 6 GHz) when communicating with ground stations. 3

4 SATCOM Product from Rockwell Collins ( 4

5 14.2 Navigation Systems With advancements of electronics (solid state devices), microprocessors and digital signal processing, navigation systems have been improved over the years. Various systems are available for different applications. Automatic Direction Finder System (ADF): To determine the aircraft s position or direction of the radio stations being received. The principal units of an ADF system are a radio receiver, which includes the amplifiers and various other electronic components, a loop antenna, a sense antenna, a radio magnetic indicator, and a remote control unit, or control panel. Instrument Landing System (ILS): To allow pilots the opportunity to land their aircraft with the aid of instrument references from glide slope transmitter (provide horizontal direction reference and a vertical reference) and runway localizer (produce directional reference signal). If an airplane is approaching the runway and is above the glide path, the 90 Hz signal will predominate; and if the airplane is below the glide path, the 150 Hz signal will predominate. Other systems: Tactical Air Navigation (TACAN), Microwave Landing System (MLS) or Time reference Scanning beam Microwave Landing System (TRSB), Radio Tuning Systems, Flight Management System (FMS) 14.3 Long range Navigation Systems LOng Rang Navigation (LORAN) is a system that operates in the LF range (30 to 300 khz) and utilizes pulse transmitting stations to provide the signals necessary for navigational computation. Inertial Navigation System: The advantage is no external radio signals are required. The system determines an aircraft s position by using Newton s laws of inertia. Global Positioning System (GPS): The system consists of three independent segments: the space segment, the control segment and the user segment. The basic idea is to know the distance and location of three or more points (from satellites), exact location can be determined. The satellites transmit a location and timing signal to the user s receiver. The distance to a satellite is determined by measuring the travel time of the transmitted signal. Knowing the speed of radio wave propagation (the speed of light), the receiver calculates the distance to the satellites. See Fig , pp Integrated Navigation and Flight Systems: A completely integrated navigation and flight system includes flight instrumentation, navigation systems, communication systems, and the automatic flight system. Air traffic Control (ATC) Transponder: Transponder is an automatic receiver and transmitter that can receive a signal from a ground station and then send a reply back to the station. There are three modes of transponder: A, C and S (read details on page 321). 5

6 Traffic Alert and Collision Avoidance System (TCAS): Major components are 1) the receiver transmittercomputer unit, 2) two display units, 3) one or two mode S transponders, 4) a system with control panel and 5) the required antennas. If the receiver identifies a potential threat, an aural and visual advisory is displayed to the flight crew. The resolution advisory will offer either corrective or preventive maneuver that will help to avoid the collision. TCAS does not control the aircraft, but it only offers suggested maneuvers to the flight crew. Radar Altimeter: Radar altimeters were developed to give an accurate indication of aircraft altitude above ground level (AGL). It works by transmitting a VHF signal downward from the aircraft and receiving the reflected signal. A radar altimeter can determine the aircraft s AGL altitude. Integrated Avionics Processor System (IAPS): This system is designed to function as a central distribution network for virtually all the avionics of an aircraft. It coordinates many systems such as weather radar, instrument display unit, flight management system, flight control system, radio sensor system, aircraft data acquisition system, air data system and the altitude heading system. Flight Data and Voice Recorders: The system must monitor both flight parameters and flight deck voice activities. A flight data recorder is housed in a crushproof container located near the tail section of the aircraft Radar RADAR (RAdio Detecting And Ranging): Radio equipment which utilizes reflected pulse signals to locate and determine the distance to any reflecting object within its range. This equipment was developed to a high level of performance by Great Britain and the United States during World War II for the detection of enemy aircraft and surface vessels. The air carrier industry quickly recognized the advantages of early weather detection using radar. Radar operates on an echo principle in which high energy radio waves are directed in a beam toward a reflecting target. The beam of pulses is actually something like a stream of bullets from a machine gun, with a relatively long space between each pulse of energy. When the pulse of energy strikes the target, which may be a mountain, rain clouds, or an airplane, a portion of the pulse is reflected back to the receiving section of the radar. At A the pulse has just been emitted from the airplane radar antenna. At this point a pip appears on the radar scope At C the pulse is striking a rain cloud. A portion of the pulse is reflected by the cloud and returns toward the airplane, as shown at D. When the reflected pulse reaches the airplane at E, a second, smaller pip appears on the radar screen. The time between the two pips indicates the distance from the airplane to the cloud. At F another pulse is emitted from the radar antenna. A typical radar signal may consist of a carrier wave of 8,000 MHz broken into pulses with a duration of 1 μsec and spaced at intervals of 1/400 s or 2,500 μsec. This would be a ratio of roughly 2,500:1 for the time of no signal to the time of signal. It must be pointed out that the ratio of the length of a pulse to the time of no signal varies considerably with the frequency, which range from 1000 to 26,500 MHz. 6

7 Two of the most commonly employed scans for radar are the A scan and the P scan. The A scan produces a horizontal line on the face of the CRT monitor as the beam of electrons moves across the fluorescent surface. The horizontal line is used to establish the distance of the target from the radar transmitter. The P scan of radar scope may be called the plan position indicator (PPI), since it indicates both the distance and direction (azimuth) of the target. On the face of the PPI scope, the time trace starts at the same time that a pulse is transmitted from the radar antenna, and the reflected pulses cause bright spots along the trace line. Type A Type P 7

8 Figures show the application of radar system in military (L) and passenger (R) aircrafts. A weather mapping system is basically a radio receiver designed to detect thunderstorm activity and display a map of that activity on a display. The convective wind shear creates static electric charges that must discharges when they reach a certain voltage level. Since the number of static discharges increases with the severity of the storm, a weather mapping system can count the discharges to determine the storm s intensity. References: Textbooks # 1 and # 2 EE Aircraft Electricity and Electronics Asst. Prof. Thavatchai Tayjasanant, Ph.D. 8