There are two classes of emergency message:
Distress : A condition of being threatened by serious and/or imminent danger and of requiring immediate assistance.
Urgency : A condition concerning the safety of an aircraft and other vehicle, or of some person on board or within sight, but which does not require immediate assistance.
A message will contain as many as possible of the following items :
MAYDAY MAYDAY MAYDAY (for distress messages)
PAN PAN, PAN PAN, PAN PAN (for urgency messages)
Name of the station addressed (time permitting)
Identification of the aircraft
Nature of the emergency
Intention of the person in command
Present position, level and heading
As much other information as time permits.
When a pilot has given certain items of information normally associated with an emergency message but has not prefixed the transmission with ‘MAYDAY’ or ‘PAN’, the controller is to ask the pilot if he wishes to declare an emergency. If the pilot declines to do so, the controller may, if he thinks it appropriate, carry out the necessary actions as if the pilot had declared an emergency. The term ‘fuel emergency’ has no status in the UK and controllers are not required to give priority to aircraft with a reported shortage of fuel unless an emergency is declared.