Pan-pan
Appearance
A call of pan-pan is a very urgent message concerning the safety of a ship, aircraft or other vehicle, or persons on board who do not require immediate assistance. It is distinct from a <a href=http://en.wikipedia.org/wiki/Mayday>mayday</a> wich is used when an aircraft and its occupants are threatened by grave and imminent danger and require immediate assistance. Thus, pan-pan indicates urgency whereas mayday indicates distress.