Emergency Definitions

ICAO has some definitions concerning emergency procedures.

Emergency phase. A generic term meaning, as the case may be, uncertainty phase, alert phase or distress phase.

Uncertainty phase. A situation wherein uncertainty exists as to the safety of an aircraft and its occupants.

Alerting phase. A situation wherein apprehension exists as to the safety of an aircraft or its occupants.

Distress phase. A situation wherein there is reasonable certainty that an aircraft and its occupants are threatened by grave and imminent danger or require immediate assistance.

Emergency procedures.

Emergency is a serious event that needs immediate action.

Summarizing aeronautical experience a list of most common reasons for the crew to declare an emergency can be made: mid-air explosion, serious fire in the cabin or engine, oil or door warning lights, loss of an engine, bird strikes, illness on board. However, this list will never be comprehensive and complete. Thus, each emergency must be treated as an event of its own. It may be similar to other emergencies, but there hardly could be two identical in every respect. That is why it is totally impossible to define instructions for all cases and write such a document as phraseology for emergencies. Nevertheless, there are some standard procedures which help to prevent chaos and make controller's work organized and regulated.

An aircraft under emergency gets priority over other aircraft. An aircraft in distress informs ATC using radiotelephony signal MAYDAY, radiotelegraphy signal SOS. The aircraft in distress sets its transponder mode A code 7700.

An aircraft having some difficulties but which does not need immediate assistance can inform about it switching on and off its landing lights or flashing its navigation lights in a way different from the normal one.

An aircraft which has an urgent message concerning people safety, other aircraft or vehicle transmits radiotelegraphy signal XXX or radiotelephony signal PAN.

In some cases it can be difficult to determine into which of the categories a particular incident falls and in other cases it is quite clear. The English used in these events can be confusing and often does not give the information a controller needs to make a reasonable assessment of the situation. The pilot may not be proficient in the use of English outside the standard laid down phraseology. And there are no laid down phraseologies for emergencies. If in doubt as to exact nature of the problem, then ask for clarification. Never forget that one unusual situation can lead to another, and they can overlap.

Inform your supervisor. He will be able to do most of the liaison which will be needed. Do not forget your other traffic. The necessity of transferring all the rest traffic to another frequency may arise. Radio silence may be imposed on all traffic except the flight in emergency.

Specific procedures for the North Atlantic airspace

If the pilot is unsure of the vertical or lateral position of the aircraft or the aircraft deviates from its assigned altitude or track without prior clearance, then the pilot must take action to minimize the potential for collision with aircraft on adjacent routes or flight levels.

In this situation the pilot must alert adjacent aircraft by making maximum use of aircraft lights and broadcasting position, flight level and intentions on 121.5 MHz (or 131.8 as a back up).

The pilot should advise ATC as soon as possible of a situation and if possible request an ATC clearance before deviating from assigned route of the flight or flight level.

If a revised ATC clearance cannot be obtained timely and action is required to avoid potential conflict with other aircraft, then the aircraft should fly at an altitude or on a track where other aircraft are least likely to be encountered.