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.