Aeronautical Communications Equipment and Frequency Management
Aeronautical communications equipment and frequency management
The exam checks that you know what the radio in the aircraft does, which frequencies exist, how channels are named, and how to protect the aeronautical spectrum from interference.
The VHF set
Civil VHF communications use amplitude modulation in the band 117.975–137.000 MHz. Propagation is line-of-sight, so usable range rises with altitude - about 40 nm at 1,000 ft and well over 150 nm at high level. Controls: on/off and volume, squelch, frequency selector, transfer/standby, PTT on yoke or headset, and a guard receiver commonly set to 121.500 MHz.
Channel spacing
Many states have moved from 25 kHz to 8.33 kHz spacing, fitting three channels where one used to fit. The channel name is not the carrier: within one old 25 kHz block you will now see names such as 118.000, 118.005 and 118.010, while the actual carriers are spaced 8.333 kHz apart. Channel names are multiples of 5 kHz - a name ending in 5 is the giveaway. Know which spacing applies in your FIR before you dial.
Other systems
121.500 VHF and 243.000 UHF are the emergency channels; 406 MHz is the COSPAS-SARSAT ELT frequency, with 121.5/243 for local homing. HF (2–30 MHz, upper sideband) covers oceanic and remote areas, often with SELCAL so the crew is alerted by a chime instead of a listening watch. ACARS and CPDLC carry datalink messages.
Worked example
You are handed 118.7 and told to contact the next unit. Dial 'one one eight decimal seven' and check the standby window before transferring. If the unit replies 'say again', confirm you selected the channel named 118.700 and not 118.705 - an 8.33 kHz mis-selection is silent, not noisy.
Traps
A stuck PTT blocking the frequency; selecting a standby frequency without transferring it; routine calls on the guard frequency; reading frequencies in a non-standard format.