Radio contact with ATC was lost over a longer period. In such cases ATC has the possibility to contact aircrafts over the emergency frequency via 121.5 MHz. In the above mentioned case the emergency frequency has been set on low volume due to unauthorized interferences. This situation lead to the interception by a military aricraft.
Concerns have been raised about the perceived misuse of 121.5 MHz. It has been reported that "chatter" conducted predominantly by General Aviation (GA) pilots, sometimes reaches such intensity that crews turn down or deselect the frequency to minimise disruption on the flight deck.
According to ICAO Annex 10 - Volume II, an aircraft shall continuously guard the VHF emergency frequency 121.5 MHz in areas or over routes where the possibility of interception of aircraft or other hazardous situations exist, and a requirement has been established by the appropriate authority.
The emergency channel (121.5 MHz) shall be used only for genuine emergency purposes, as broadly outlined in the following:
- to provide a clear channel between aircraft in distress or emergency and a ground station when the normal channels are being utilized for other aircraft;
- to provide a VHF communication channel between aircraft and aerodromes, not normally used by international air services, in case of an emergency condition arising;
- to provide a common VHF communication channel between aircraft, either civil or military, and between such aircraft, and surface services, involved in common search and rescue operations, prior to changing when necessary to the appropriate frequency;
- to provide air-ground communication with aircraft when airborne equipment failure prevents the use of the regular channels;
- to provide a channel for the operation of emergency locator transmitters (ELTs), and for communication between survival craft and aircraft engaged in search and rescue operations;
- to provide a common VHF channel for communication between civil aircraft and intercepting aircraft or intercept control units and between civil or intercepting aircraft and air traffic services units in the event of interception of the civil aircraft.
This FOCA publication will not guarantee any revisions and new publications on this topic.