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Navigation and Communication Systems

Navigation and Communication Systems. Prepared by: Lindsay V. Oczak Fall 2000. Communication Systems. VHF HF ACARS / AIRCOM Secal decoders SATCOM. COMM Radios. Two types commonly used for communication: VHF

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Navigation and Communication Systems

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  1. Navigation and Communication Systems Prepared by: Lindsay V. Oczak Fall 2000

  2. Communication Systems • VHF • HF • ACARS / AIRCOM • Secal decoders • SATCOM References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  3. COMM Radios • Two types commonly used for communication: • VHF • VHF (very high frequency) is used by air traffic control and operates in the VHF band between 118 and 136.975 MHz • Range is 30 miles at 1000 feet and approximately 135 miles at 10,000 feet • HF • HF (high frequency) used for extended range communication operates between 2.0 and 29.999 MHz References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  4. VHF & HF Systems • Both the VHF and HF system utilize transmitters, receivers and antennas. • Transceivers are units that include both the transmitter and receiver in one unit. • VHF and HF systems are completely independent of each other and utilize their own transmitters, receivers and antennas. • VHF systems are found in any aircraft capable of two way radio communication and are largely used for controlling traffic. • HF systems are found in large transport category aircraft that may need to communicate over large distances (overseas). References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  5. ACARS (ARINC Communication Addressing and Reporting System) • Transmits short messages from aircraft systems to central facility in Chicago • Two modes used • Demand mode – Flight crew transmits • Polled mode – Ground station transmits • Note: AIRCOM is the European and Australian equivalent References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  6. Secal Decoder • Used to “filter” messages on COMM radio receivers • Aircraft are assigned a tone combination for secal unit to monitor. • Secal unit alerts the crew to an incoming radio transmission References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  7. SATCOM • Utilizes satellites for transcontinental flight communications • More reliable the HF communication • Range is between latitudes 75º N and 75º S • Uses three sub-systems • Ground earth station • Aircraft earth station • Satellite system • Capable of of transmitting information from many different sources • AIRCOM, ACARS, flight-crew communications, passenger telephone, telex and fax References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  8. VOR ADF ILS LOC GS Marker beacons Radio altimeters DME GPS Transponders ELT Navigation Systems References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  9. VOR (VHF omni-directional range) • VOR’s operate between 108.0 to 117.9 MHz frequency band • System includes • VOR ground station or transmitter • VOR receiver in aircraft • In light aircraft this is often combined with the comm radio • Aircraft display • CDI course deviation indicator • TO/FROM indicator • OBS omni-bearing selector or course selector • ON/OFF flag to determine field strength • Antenna References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  10. VOR Operation • VOR station continually transmits an infinite number of radials. • The VOR receiver in the aircraft receives the signal and operates the visual indicator. • The pilot determines the bearings of VOR station with respect to the aircraft. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  11. ADF (automatic direction finder) • Operation • The ADF receives NDB (non-directional beacon) signals in the 19 to 535 kHz AM broadcast low band. • The ADF display pointer (RMI or radio magnetic indicator) will indicate the relative bearing to the selected AM band in that range. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  12. ILS (instrument landing system) • Combination of several systems to provide pilot with the ability to land in conditions with poor visibility. • Components • LOC (localizer) • Horizontal reference • GS (glide slope) • Vertical reference • Marker beacon • Distance from runway • Radio altimeter • Very accurate altitude measurement • DME (distance measuring equipment) • Very accurate distance measurement References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  13. LOC (localizer) • Combined with the VOR system • Utilizes 1 of 40 ILS channels between 108.10 to 111.95 MHz. • Operation • The ground transmitter is located at the far end of the runway and provides a valid signal up to 18 NM • The CDI (course deviation indicator) gives full fly left/right deviation of 700 feet at the runway threshold. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  14. GS (glide slope) • Utilizes 1 of 40 channels between 329.15 to 335.00 MHz. • Operates on the same principles as the LOC. • The GS transmitter is located between 750 and 1250 ft. from the approach end of the runway and is offset 250 to 650 ft. • The indicator is either an ADI (attitude-director indicator) or HSI (horizontal-situation indicator). • Both indicators combine other indications for ease of use. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  15. Marker Beacons • Marker beacon receivers operate at 75 MHz and sense the audio signature of 3 types of beacons. • Blue outer marker (5 miles from end of runway) • Modulated with 400 Hz • Amber middle marker (2/3 mile from end of runway) • Modulated with 1300 Hz • White inner marker (1500 feet from end of runway) • Modulated with 3000 Hz • Operation • As the aircraft flies over each maker the appropriate light will flash and an audible sound may be heard. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  16. Radio Altimeters • The radio altimeter provides better accuracy then the pressure sensitive altimeters. • Operation • The transmitter sends out a VHF signal downward then receives the reflected signal. • The transmitter-receiver unit calculates the time needed for the signal to transmit and return to obtain AGL (above ground level) altitude. • DH (decision height) used for instrument landings may be incorporated in this system. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  17. DME (distance measuring equipment) • Range is up to 199 NM at the high end of controlled airspace based on line of sight with accuracy of ½ mile or 3% of the distance. • DME operates on frequencies from 962 to 1213 MHz. • Operation • The aircraft transmitter sends out paired pulses at specific spacing. • The ground station receives the pulses and then responds with paired pulses at the same spacing but a different frequency. • The aircraft receiver measures the time it takes to transmit and receive the signal which is transmitted into distance. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  18. GPS(global positioning system) • Utilizes a 24 hour satellite system that is accurate within 100 meters and is unaffected by weather. • Has 3 independent segments • Space segment – satellites • Control segment – ground based monitoring • User segment – aircraft • Database updating and antenna maintenance are the primary concerns to the GPS user. • Will be the most widely used system in the near future. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  19. Transponders • An automatic receiver and transmitter that can receive a signal (be interrogated) from a ground station and send a reply back to the station. • Used to identify aircraft on radar • Identification or squawk is 1200 for VFR flight • Squawk assigned by ATC for IFR flight • Used for emergency transmissions References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  20. Transponder operation • Three modes of operation • Mode A • Location only, non-altitude reporting • Mode C • Location and altitude reporting • Mode S • Can do Mode A and C and also responds to TCAS (traffic collision avoidance systems) References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  21. ELT (emergency locator transmitter) • Required on all aircraft to provide a signal on crash landings that will enable search aircraft or ground stations to locate the aircraft. • Consists of a dual frequency radio transmitter and battery power supply with a whip antenna. • Transmits on international distress signals of 121.5 (civil) and 243.0 (military) MHz. • Activated by impacts of 5g or more or manually. • Transmits up to 100 miles at receiver altitude of 10,000 ft for 50 continuous hours. • Located in an area of the aircraft where impact damage will be minimal. • Tail cone area • Aft top of cabin References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  22. ELT Testing • Three switch positions: AUTO, OFF and ON • Testing may be done under the following conditions: • Tune VHF COMM receiver to 121.5 MHz • Only within the first 5 minutes of an hour • Only three pulses should be activated • Listen for an audible signal when switched to ON position References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  23. ELT Servicing • The battery pack must be changed in accordance with the date stamped on the unit. • The battery pack must also be replaced or recharged when it has been in use for more than one cumulative hour, or when 50% of the useful life or charge has expired. • Testing should be performed regularly. • Inspections must be made every 12 calendar months. • Regulations FAR Part 91.52 References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  24. Inspections for NAV/COMM Equipment • System inspections • Antenna inspections • Static discharge inspections • Operational checks or any additional inspections required by the manufacturer References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  25. Inspection of NAV/COMM Systems • Inspect the condition and security of equipment including wiring bundles. • Check for any indications of overheating in the equipment or wiring. • Check for poor electrical bonding • Requirements are specified by the manufacturer. • Cables should be kept as short as possible, except antenna cable which have a specific length determined in installation. • Proper bonding on the order of .003 ohms is important to the performance of avionics equipment. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  26. Inspection of NAV/COMM Systems • Check instruments and radios for secure attachment to the instrument panel. • Check that all avionics are free of dust or contaminates. • Equipment ventilation openings must not be obstructed. • Check all plugs, connectors, switches, controls for operation and condition. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  27. Inspection of NAV/COMM Systems • Check all instruments for placards as needed. • Check all instrument lighting and annunciator lights for operation. • Check circuit breaker panel for placards labeling each circuit breaker installed. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  28. Antenna Inspection • Check for: • broken or missing antenna insulation • lead through insulators • Safety wires • Cracked antenna housing • Missing or poor sealant at base of antenna References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  29. Antenna Inspection • Check for: • Correct installation • Signs of corrosion • Condition of paint/bonding and grounding • Bonding of each antenna from mounting base to the aircraft skin. • Tolerance 1 ohm, maximum References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  30. Inspection of Static Dischargers/Wicks • Check for: • Physical security of mounting attachments, wear or abrasion of wicks, missing wicks, etc. • Assurance that one inch of the inner braid of flexible vinyl cover wicks extends beyond the vinyl covering. • Assurance that all dischargers are present and securely mounted to their base. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  31. Inspection of Static Dischargers/Wicks • Check for: • Assurance that all bases are securely bonded to the skin of the aircraft. • Any sign of excessive corrosion or deterioration of the discharger tip. • Any lighting damage shown by pitting of the metal base. • The ohm value of the static wick itself per manufacturer’s instructions. References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

  32. Additional Inspections • Transponder • Per FAR 14 Part 91.411 and 91.413 • ELT • Per FAR Part 91.52 • Functional checks of all other COMM and NAV systems per the manufacturer’s instructions References: Aircraft Electricity and Electronics pg: 294-328, AC 43.13-1B Chapter 12 Section 2

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