Communication failure

Communications in civil aviation are conducted using radiotelephony (RTF).

The frequencies used are decided by the International Telecommunications Union (ITU). Civil aviation makes heavy use of the very high frequency (VHF) bands. The maximum distance over which an aircraft flying at high altitude can communicate with a ground station is approximately 350 kilometres.

If two-way contact between an aircraft and air traffic control is lost, the situation is referred as a “communication failure”. To determine whether the plane is still able to receive messages, the controller can ask the pilot to perform a specified manoeuvre that can be observed on the radar screen or to enter a new secondary surveillance radar (SSR) code. These are codes used to identify individual flights on radar and are unique to each aircraft.

The controller may try to re-establish radio contact by calling the aircraft on the emergency frequency or on one of the published alternative frequencies for the area in question. The pilot can also enter a special SSR code, 7600, which indicates a communication failure.

When communication is lost, the pilot follows the standard flight procedures set out in the Aeronautical Information Publication (AIP). In most cases, contact is re-established quite quickly. If it is not, that may indicate unlawful interference with the aircraft – a hijacking.