Communications
What the paper tests
Communications covers radiotelephony phraseology, readback requirements, distress and urgency procedures, and the equipment: VHF and HF radio, SELCAL, ACARS, CPDLC and ADS-C, plus lost-communication procedures.
Core rules
- VHF is essentially line-of-sight; range grows with the square root of antenna height.
- HF is used over oceanic and remote areas where VHF coverage does not exist; SELCAL lets a crew be alerted without continuous listening watch.
- Read back safety-critical items: clearances, runway assignments, hold-short instructions, altimeter settings, frequencies and headings.
- MAYDAY (three times) declares distress; PAN-PAN (three times) declares urgency. 121.5 MHz is the civil emergency frequency, 243.0 MHz the military equivalent.
- If communications fail, squawk 7600 and follow the published lost-communication procedure.
Worked example
An aircraft at 35,000 ft and a ground station at 100 ft. VHF range ≈ 1.23 × √35,000 = 1.23 × 187 = 230 nm, plus 1.23 × √100 = 12 nm for the station, giving about 242 nm. That explains why oceanic sectors need HF or satellite links, and why crews must report position before VHF coverage is lost.
Traps
Answering a clearance with 'roger' instead of a full readback, omitting your callsign when replying, confusing MAYDAY with PAN-PAN, and transmitting a distress call on the wrong frequency.