/Aircraft Communication
   /Radio Telephony

ATC Light Gun Signals

Radio Communications Failure

Most general aviation aircraft flying under VFR rules are not equipped with satellite communications, we therefore rely on line of sight VHF or long range HF communications. As long as we are within range of the radio station we can talk to ATC. But in mountainous areas, or if the radio technically fails or for some other unknown reason and we lose communication the pilot must take action to remedy the situation.

Communications failures can arise from a number of sources: equipment problems, being out of range from the other station, radio interference, blocked transmissions, callsign confusions and English language skills below the level of what is required of even just refuse to communicate in English, despite the ICAO English Language requirement.

This section will investigate the options available to the pilot to re-establish radio contact and what other options there are should it fail completely.

Loss of Communication

Pilots are expected to exercise good judgment when confronted with a radio communications problem. They may deviate from the rules to the extent required to meet an emergency. The rules also make it clear what the pilot can do should he/she fly IFR. But first thing to do is to keep calm and do not panic!


During preflight make sure that you have the correct frequencies with you: check the AIP, NOTAMs, approach and/or enroute charts. Preflight also means that you need to check communications availability for the airports and the route you plan to use. If not sure then a phone call with your destination will solve that problem, also ask if they accept NORDO (No Radio) aircraft.

Garmin SL40 Aircraft Radio

Radio's can become complex equipment when they are integrated into Garmin G500 / G1000 systems like EFIS. Standalone Icom, Bendix King or Apollo/Garmin radio's are really easy to control. Having the pilots quick reference manual in your flight bag or with the aircraft documentation or manual can be a very big help. It will save the day should you become confused about any function of the radio.

ATC light gun

Some aviation charts depict them: ATC light gun signals. Make sure you know them by heart or carry a copy of their meaning with you. Practice these signals every once in a while.

Frequency change

If contact can not be established after a frequency change, go back to the previous frequency or channel and verify with the controller that you have the correct frequency. This is first thing you must do in this case.

Second radio

If you suspect that your radio has failed and you have a second one, set that frequency in the other radio and try again. When I fly an aircraft with multiple radio's I plan to use all of them, and during a handover I set the next frequency into the other radio and use that one. This way, I always have both radio's checked and functional. Should I need to switch back, its done within a blink of an eye on the intercom panel.

Squelch setting

A squelch is used to suppress the white noise when no station is transmitting, turn the knob clockwise until the noise just about disappears (on radio's with an automatic squelch you need to pull or push the volume knob).

Sometimes, after switching and verifying that you have the correct frequency and that the radio is operating correctly, it might be that you are just to far away (or flying too low) for the next station. Its signal strength is just too weak to open the squelch you will hear nothing.
First thing I do is to open up the squelch manually (pull/push the volume knob) and listen to the noise/static and other aircraft and retransmit when able. Chances are that you hear them calling you just above the noise level. By the time you get closer, the signal strength will have improved enough so that you can use the squelch again.


Some of these also have a squelch setting, this is to suppress noise from the cabin when talking to your passengers or copilot. Make sure to set it so that it closes just above the background noise.

Radio Failure

It will not happen that often but radio's can fail and having a second one on standby will save the day. Should it happen, try pulling the fuse (if not popped already) wait a couple of minutes and push it in again. This might reset the radio. Should this fail then and you have only one radio, set 7600 on the transponder and determine if you need to divert to an airport where NORDO aircraft are allowed. It is advisable to call ATC by phone after landing to explain the situation.


VHF communications rely on antennas to be in line of sight of each other to be able to receive their signals. Should you not hear the other station then climb, if possible, a couple of thousand feet. This will improve the range in which you can contact stations.

HF communications rely on radio wave propagation by the Earth's Ionosphere and line of sight is not so much of an issue here.


At certain times you may find that other, possibly higher flying aircraft, are willing to relay your message to the ground station. Sometimes even without asking, because they can hear you and the ground station and its obvious to them that you can not reach or hear ATC and vice versa.


Aircraft Transponder

The transponder code for lost communications is 7600 in any mode (A/C/S). Setting this code will ring bells in ATC facilities and you will most definitely get their attention! Again, make sure to explain the situation after landing. Don't ask me how I know...


If all else fails and your destination is a controlled airport where radio communications are mandatory, then by all means divert to an airport where you can land without a radio and have your radio checked by a radio shop before you continue on to your final destination. Overflying the signal area at a safe altitude before entering the circuit/pattern is a wise decision at that time.

Written by EAI.

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