Aircraft Communication Systems

1. Aircraft CommunicationSystems DGCA: ATA-23 Presented by Arnav Mukhopadhyay URL:http://gudduarnav.com/

2. VHF COMMUNICATIONS

3. VHF Communications: Specifications • Modulation Type: Amplitude Modulation (AM) (Vertically Polarized, Omnidirectional Whip Antenna) • Receiver Type: Single or Double Conversion Superheterodyne Receiver • Frequency Band: 118 – 135.975 MHz • Channel: 720 channels with Bandwidth of 25 KHz (Previously, 360 channels @ 50 KHz) • Operation Mode: Single Channel Simplex (TX and RX frequency is Same) • VHF communication is Line of Sight. • Satellite Communication: AM Single Channel Simplex + FM Double Channel Simplex(Double Channel Simplex = Frequency of TX and RX are different) • Satellite Communication Standard: ARINC 566 • Output Impedance is 50  (Max. 1.5:1 VSWR) with 25 W power and input supply of 28 V

4. VHF Communications: Transceiver Standby Frequency (MHz) In Use Frequency (MHz) Volume Control Switch between In-Use And Standby frequency • Mode Selection: • AM • SATCOM King KX 155A TSO

5. VHF Communications: Transceiver King KY 196 Simplified Block Diagram

6. VHF Communications: Transceiver • King KY 196 Transmitter Block Diagram • Sidetone represents that Transmission is Active • PTT (Push To Talk) button activates modulation • RF Drive is shorted to ground through TR Diode when PTT is not depressed • SMO represents Stabilized Master Oscillator

7. VHF Communications: Transceiver • King KY 196 Receiver Block Diagram • Sidetone indicate that Audio Output of Receiver must be activated

8. VHF Communications: Transceiver Controls • Switch to select In-use and Standby Frequencies, and another switch to switch between the frequencies • Frequency Knob: Concentric knob to tune to the frequency to use. Change takes place to the current frequency channel selected • Volume Control: Volume control potentiometer to control audio amplitude before it is fed to AIS (Audio Integrating System) • Squelch Control: Squelch threshold is set using a potentiometer. Audio Level above Squelch Threshold opens the Squelch Gate • Mode Selector Control: Select Normal AM or SATCOM mode of operation • ON-OFF Switch: Energizes the master relay to switch on or off the unit • Receiver Sensitivity Switch: Select either of Normal or Sharp selectivity. SATCOM mode requires Sharp Selectivity, which is automatically selected

9. HF COMMUNICATIONS

10. HF Communications: Specifications • Range: Beyond VHF communication (Line of Sight) Range • Standard: ARINC 559A • Modulation: Single Side Band AM (SSB-USB) preferred; AM can be used • Power: 200 W (nominal). 300 W (SSB mode). 500 W (normal AM mode) • Antenna: 50  through ATU (Antenna Tuning Unit), Max. 1.3 : 1 VSWR • Antenna Type: Notch Antenna, Probe Antenna • Frequency Band: 2.8 – 24 MHz (1 KHz stepping) for Civilian Aircraft; 2 – 30 MHz (0.1 KHz stepping) for Military Aircraft • Static Discharge: High Resistance path of about 6 M between Antenna, ATU and Earth ground

11. HF Communications: Typical Installation

12. HF Communications: Transceiver Block Diagram

13. SELCAL Selective Calling

14. SELCAL • Allows Ground station to call an Aircraft or Group of Aircraft on HF or VHF COM • Calls will go through without requiring the Pilot to monitor the station continuously • Ground station transmits a special code to the Aircraft, representing the code of the Aircraft • Code is transmitted in 2 bursts: 1 s (+/-0.25 s) Pulse with 0.2 s (+/- 0.1 s) Silent • Code uses 4 tones per call, with 90 % carrier modulation • Tone Frequency: where • Tone Frequency varies from 312.6 to 1479.1 Hz • Tones can have letters A to S, assigned using Flight Number or Aircraft Registration • May not comply with ARINC 596. Documented in ARINC 714A. User must select the SELCAL (HF or VHF frequency) channel to listen to.

15. SELCAL • Upper Side Band AM Modulation • Bandwidth: 1500 Hz • Symbol Rate: 1 symbol/sec SELCAL Spectrum SELCAL Pulse Format

16. AIS Audio Integrating System

17. AIS: Audio Integrating System • Allows integration of various Aircraft’s Audio System with Cockpit Audio Speaker (and Mic) systems Boeing 747: Connection layout between Flight Interphone and Various Communication systems

18. AIS: Audio Integrating System: Services • Flight Interphone: Allows communication between Flight Crew members to communicate with each other in the Cockpit, and with Ground station. When Oxygen mask is not deployed, Boom Mic is connected. When Oxygen mask is deployed, Mask Mic is connected. • Cabin Interphone: Allows communication between Flight Crew and Cabin Crew • Service Interphone: Allows communication between multiple Ground Staff, and between Ground Staff and Flight Crew / Cabin Crew. • Passenger address (PA): Broadcast communication to passengers. Used by Flight Crew / Cabin Crew. • Passenger Entertainment System: Allows streaming videos and music to passenger. • Ground Crew Call System: Allows Ground crew to alert flight crew, and vice versa. Includes SELCAL, ACARS • Cockpit Voice Recorder: Record all audio communication for subsequent investigation (esp. during accident)

19. Flight Recorder

20. Flight Recorder • Electronics Data Recording Device placed in Aircraft for use in investigation of Aircraft Accident or mishaps • Types of Flight Recorder devices: • Flight Data Recorder (FDR) • Cockpit Voice Recorder (CVR) • Devices must withstand severe shock or extreme environmental conditions: • for 6.5 millisec. • Minimum Temperature of • Specifications mandated by EUROCAE (EURopean Organization for Civil Aviation Equipment) ED-112 • FDR+CVR combination must conform to recorder equipment specifications indicated in ICAO Annex 6 (Vol. I, III, Attachment D) Typical Flight Recorder CVR, FDR with Underwater Locator Beacon Underwater Locator Beacon

21. Flight Data Recorder • Records specific aircraft performance parameters. • ICAO Annex-6 – Operations of Aircraft Vol. I, III for Type-I FDR require following parameter recording: • Flight Path • Speed • Altitude • Engine Power • Configurations • Operations • ICAO Annex-6 – Operations of Aircraft Vol. I, III for Type-II and II-A require following parameters to be recorded: • Flight Path • Speed • Altitude • Engine power • Configuration of Lift and Drag devices A typical FDR with Underwater Locator Beacon

22. Flight Data Recorder • Recording Media: • Magnetic Tape • Digital Recorder (Boeing 737, Airbus A320 using Digital Avionics systems) • Solid State Technology (can provide atleast 4 times the capacity of that of Magnetic Tape) • Specifications: • Fire: • Shock: 3400 G for 6.5 ms • Crushing Pressure: 5000 pounds for 5 min each axis • Survive immersion in aircraft fluids for over 24 hours • Survive immersion in sea water for atleast 30 days A typical FDR with Underwater Locator Beacon

23. Cockpit Voice Recorder • Records audio from speaker and MIC from Flight Deck crew (Pilot and Flight Crew) • ICAO Annex-6 – Operations of Aircraft Vol. I requires CVR to record atleast 30 min of Audio (2 hours for aeroplanes (1 Jan 2003)) • Update 1 Jan 2007: CVR is included inside FDR, will record all data communications over Aircraft Data Link Bus. • CVR inside FDR allow correlation of Audio Recording with Aircraft Sensor data • All recorded data for CVR in FDR are properly time stamped A typical CVR with Underwater Locator Beacon

24. Underwater Locator Beacon (ULB) A: End Cap with a Water activated Switch alongside metal envelope B: Pulse generation circuit within urethane cylinder C: Piezoelectric Transducer to convert electric pulses to Acoustic Pulses D: Power Source (non-rechargeable Lithium battery) Submarine acoustic landscape near Urca beach, Rio de Janeiro. The ULB was placed at a distance of 150 m from the hydrophone. Detected pings are indicated by arrows

25. Emergency Locator Transmitters (ELT)

26. Emergency Locator Transmitter (ELT) • ELT is a Radio beacon used to locate airplanes • ICAO Recommends the ELT beacon to be activated automatically due to impact or manually activated • The ELT beacon must produce distinct signature on designated frequencies for proper identification • ELT is part of International Satellite System for Search And Rescue (SAR) – CORPAS-SARSAT • LEO Satellites detect ELT signal locations using GPS trilateration or Doppler Triangulation techniques (or both) • ELT signal transmission occurs on 406 MHz (Phase-Coded signal) and 121.5 MHz (ICAO, Annex 10, Vol. V) • All airplanes on long route and certain overwater flying Helicopter must be equipped with Automatic ELT beacons (ICAO, Annex 6, Part IIA) 406 MHz ELT Transmitter

27. Aircraft Communication, Addressing and Reporting System (ACARS)

28. Aircraft Communication, Addressing and Reporting System (ACARS) • ACARS is Digital Data Link System • Message (analogous to Mobile Paging) based communication between Aircraft and Ground System • Modern ACARS is Manual and Automatic messaging system • Ground system service provider can be either of: • Air Navigation Service Provider (ANSP): The organisation that manages flight path and flight management services • Aircraft Operator: Through sub-contractor service provider • Communication system is modelled on TELEX network system (TELEX: public switched network of teleprinters, using binary coded messaging system)

29. ACARS System ACARS System Components Ground Processing System Aircraft Equipment Service Provider • ACARS receiver on Aircraft is called Management Unit (MU) / Communication Management Unit (CMU) • CMU acts as a router for Aircraft, to access External N/W • Flight Deck printer may be present to print the ACARS message • More advanced aircraft may include Display Unit and Keyboard • Ground station operates the ACARS network through Air Navigation Service Provider (ANSP) or Aircraft Operator • Messages may be auto generated for broadcast to all aircraft. Messages may be sent to specific aircraft • The Radio link used to relay ACARS message • VDL (VHF Data Link) used for Line of Sight Communication • SATCOM. Not available in Polar Region • HFDL (HF Data Link) for long range and polar region coverage

30. ACARS Message ACARS Messages Airline Administrative Control (AAC) Aircraft Traffic Control (ATC) Aeronautical Operational Control (AOC) • Issues messages related to clearance and instructions for aircraft • Informs aircraft about pre-departure, terminal information, Oceanic clearance • Although not depreciated, but Controller Pilot Data Link Communication (CPDLC) is preferred • Communication that occurs between Aircraft and its base • Standard messages used must conform to standards laid out in ARINC Standard 618 • Upload Weather, NOTAM (Notice to Airmen) information • Download Aircraft status, position, route information, aircraft sensor data (Weather from Aircraft’s Weather Radar), Technical Performance Data (Abnormal Aircraft behaviour), housekeeping information (Passenger Information, ETA (Estimated Time of Arrival))

31. References • J. Powell, “Aircraft Radio Systems”, Himalayan Publishers (2009) (ISBN: 81-7002-091-3) • https://www.asri.aero/selcal/how-selcal-works/ • http://www.wavecom.ch/content/ext/DecoderOnlineHelp/default.htm#!worddocuments/icaoselcal.htm • https://www.skybrary.aero/ • R. Barmak, A. L. S. C. de Oliveira,, P. Sao, M. V. R. Lopes, G. Cernicchiaro, “Underwater Locator Beacon Signal Propagation on Tropical Waters”, RIO Acoustics Conference (2017) (DOI: 10.119/RIOAcoustics.2017.8349738) • https://wst.ca/beacon_tester.html