Messages Categories

The message categories in order of decreasing importance;

1. Distress
2. Urgency
3. Direction Finding
4. Flight Safety
5. Meteorological
6. Flight regularity
7. State Telegrams

Distress = Imminent danger, requiring immediate assistance

Urgency = Concern for the safety of other aircraft, vessels, vehicle or persons

Direction Finding = Related to navigation, requesting a QDM for example

Flight Safety = ATC messages, position reports, aircraft operator message of concern to flight safety

Meteorological = Aerodrome weather for example

Flight regularity = Changes in flight plan, serving of aircraft, non-routine landings, aircraft parts required

State telegrams = Transmitted by head of state, sovereigns of persons of equal rank on board an aircraft

The last 2 are transmitted on FIS frequency or other assigned by ATC to avoid interference