Declaring emergency

Mayday is an emergency procedure word used internationally as a distress signal in voice procedure radio communications.

It is used to signal a life-threatening emergency primarily by aviators and mariners, but in some countries local organizations such as firefighters, police forces, and transportation organizations also use the term. The call is always given three times in a row ("Mayday Mayday Mayday") to prevent its being mistaken for some similar-sounding phrase under noisy conditions, and to distinguish an actual Mayday call from a message about a Mayday call.

The Mayday procedure word was originated in 1923, by a senior radio officer at Croydon Airport in London. The officer, Frederick Stanley Mockford, was asked to think of a word that would indicate distress and would easily be understood by all pilots and ground staff in an emergency. Since much of the traffic at the time was between Croydon and Le Bourget Airport in Paris, he proposed the word "Mayday" from the French "m'aider", a shortened version of "venez m'aider" (meaning "come and help me").

Before the voice call "Mayday", SOS was the Morse code equivalent of the Mayday call. In 1927, the International Radiotelegraph Convention of Washington adopted the voice call Mayday as the radiotelephone distress call in place of the SOS radiotelegraph (Morse code) call.

If a Mayday call cannot be sent because a radio is not available, a variety of other distress signals and calls for help can be used. Additionally, a Mayday call can be sent on behalf of one vessel by another, using a convention called a Mayday relay.

Civilian aircraft making a Mayday call in United States airspace are encouraged to use the following format (omitting any portions as necessary for expediency or where they are irrelevant):

Mayday, Mayday, Mayday; (Name of station addressed); Aircraft call sign and type; Nature of emergency; Weather; Pilot's intentions and/or requests; Present position and heading, or if lost then last known position and heading and time when aircraft was at that position; Altitude or Flight level; Fuel remaining in minutes; Number of souls on board; Any other useful information.

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