AET Communication Systems 5 — Questions and Answers
Question 1: A CVR (Cockpit Voice Recorder) is required to retain audio from the last:
- 30 minutes of flight
- 2 hours of flight (Correct answer)
- 4 hours of operation
- 6 hours from wheels-off
Correct answer: 2 hours of flight
Current regulations (14 CFR 91.609) require CVRs to retain at least 2 hours of the most recent audio to capture enough data for accident investigation.
Question 2: Ground-wave propagation is associated with which frequency range used in aviation?
- VHF (118–136 MHz)
- HF (2–30 MHz) (Correct answer)
- UHF (300–3000 MHz)
- SHF (3–30 GHz)
Correct answer: HF (2–30 MHz)
HF radio uses both ground-wave (for short ranges) and sky-wave (ionospheric reflection for long ranges), making it essential for oceanic and remote-area communications.
Question 3: When troubleshooting a SATCOM system showing 'no log-on' status, the technician should FIRST check:
- The HPA (High Power Amplifier) bias current
- Antenna pointing, obstructions, and satellite network log-on status (Correct answer)
- The audio codec board for bit errors
- VHF radio interference on the SATCOM data bus
Correct answer: Antenna pointing, obstructions, and satellite network log-on status
A 'no log-on' indication most often results from physical blockage, antenna attitude error, or a lapsed network subscription before any internal hardware fault.
Question 4: The purpose of the 'guard' receiver in a VHF comm radio is to:
- Provide squelch to the main receiver
- Simultaneously monitor 121.5 MHz emergency frequency while operating on another channel (Correct answer)
- Block unauthorized transmissions
- Encrypt transmissions on the primary channel
Correct answer: Simultaneously monitor 121.5 MHz emergency frequency while operating on another channel
A guard receiver continuously monitors 121.5 MHz (the international emergency frequency) in parallel with the main operational channel.
Question 5: A passenger address (PA) amplifier on a transport category aircraft fails silently — no audio in cabin, no fault indication. The BEST initial test is:
- Replace the amplifier module immediately
- Inject a known audio signal at the amplifier input and measure output at speaker tap points (Correct answer)
- Check all CVR inputs for signal
- Verify ACARS datalink is not jamming PA frequencies
Correct answer: Inject a known audio signal at the amplifier input and measure output at speaker tap points
Signal injection at the amplifier input and probing the output isolates whether the fault is in the amplifier itself or in upstream audio sources and wiring.
Question 6: Which standard defines the ARINC 429 data bus commonly used to interconnect avionics including communication management units?
- MIL-STD-1553B
- ARINC 429 (DITS) (Correct answer)
- ARINC 664 (AFDX)
- RS-485
Correct answer: ARINC 429 (DITS)
ARINC 429 (Digital Information Transfer System) is a unidirectional serial data bus standard widely used on commercial aircraft to pass data between avionics LRUs.
Question 7: Which regulatory document provides minimum performance standards for airborne VHF communication transceivers installed in US-registered aircraft?
- FAA Advisory Circular AC 43.13-1B
- RTCA DO-186 / TSO-C169 (Correct answer)
- MIL-STD-461 subsection C
- ICAO Annex 10 Volume I only
Correct answer: RTCA DO-186 / TSO-C169
RTCA DO-186 establishes the minimum operational performance standards for airborne VHF comm equipment, and TSO-C169 is the FAA Technical Standard Order referencing it.
AET Communication Systems 5
A CVR (Cockpit Voice Recorder) is required to retain audio from the last: