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 it 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 1921, 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 expression "mayday" from the French m'aider ('help me'), a shortened form of venez m'aider ('come and help me'). It is unrelated to the holiday May Day.
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; this is known as a mayday relay.
Civilian aircraft making a mayday call in United States airspace are encouraged by the Federal Aviation Administration to use the following format, omitting any portions as necessary for expediency or where they are irrelevant (capitalization as in the original source):
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.
Making a false distress call is a criminal offence in many countries, punishable by a fine, restitution, and possible imprisonment.
Other urgent calls
"Pan-pan" (from the French: panne, 'a breakdown') indicates an urgent situation, such as a mechanical failure or a medical problem, of a lower order than a "grave and imminent threat requiring immediate assistance". The suffix "medico" used to be added by vessels in British waters to indicate a medical problem ("pan-pan medico", repeated three times), or by aircraft declaring a non-life-threatening medical emergency of a passenger in flight, or those operating as protected medical transport in accordance with the Geneva Conventions. "Pan-pan medico" is no longer in official use.
Sometimes the phrase "declaring emergency" is used in aviation, as an alternative to calling "mayday". For example, Swissair Flight 111 radioed "Swissair one-eleven heavy is declaring emergency" after their situation had worsened, upgrading from the "pan-pan" which was declared earlier.
However, the International Civil Aviation Organization recommends the use of the standard "pan-pan" and "mayday" calls instead of "declaring an emergency". Cases of pilots using phrases other than "pan-pan" and "mayday" have caused confusion and errors in aircraft handling.
Silencing other communications traffic
"Seelonce mayday" (using an approximation of the French pronunciation of silence) or "seelonce distress" (in actual French, silence détresse) is a demand that the channel only be used by the vessel in distress and the Coast Guard or other responding authority (and any other vessels they ask to assist in handling the emergency). The channel may not be used for normal working traffic until "seelonce feenee" or "prudonce" (see below) is broadcast. "Seelonce mayday" (followed by the name of the disturbing station) may only be sent from the vessel in distress. "Seelonce distress" (followed by the name of the disturbing station) may only be sent from a station which is not participating in the emergency traffic. The expressions "stop transmitting – mayday" and "stop transmitting – distress" are aeronautical equivalents of "seelonce mayday" and "seelonce distress".
"Seelonce feenee" (from French silence fini, 'silence finished') means that the emergency situation has been concluded and the channel may now be used normally. The call "prudonce" (from the French pronunciation of prudence, 'caution') can also be used to allow important working traffic to resume on that channel before resolution of the emergency. "Distress traffic ended" is the aeronautical equivalent of "seelonce feenee".
- Aircraft emergency frequency
- Call for help
- Distress signal
- Global Maritime Distress Safety System
- Vessel emergency codes
- "Radio Information for Boaters". US Dept of Homeland Security - US Coast Guard. 15 September 2016. Retrieved 19 September 2018.
- "Why Mayday?". Research Questions. National Maritime Museum Cornwall. Retrieved 1 May 2013.
- "It's MayDay – But That Means Trouble for Aviators". Retrieved 31 March 2018.
- "Mayday - Definition of Mayday in English by Oxford Dictionaries". Oxford Dictionaries - English.
- In 1927, the International Radiotelegraph Convention of Washington adopted "mayday" as the radiotelephone distress call Radiotelegraph Convention of Washington, page 81.
- Aeronautical Information Manual, paragraph 6-4-2, "Obtaining Emergency Assistance", Federal Aviation Administration, 1999.
- "No Joke".
- ICAO Annex 10 V2 Section 5.3
- Tim Bartlett (2009). VHF handbook. Southampton: The Royal Yachting Association. p. 53. ISBN 978-1-905104-03-1.
- "Wayback Machine". web.archive.org. 15 September 2010.
- Ranter, Harro. "Aviation Safety Network > Accident investigation > CVR / FDR > Transcripts > ATC transcript Swissair Flight 111 - 02 SEP 1998". aviation-safety.net.
- "ICAO Standard Phraseology" (PDF). SKYbrary. Retrieved 13 June 2013.
- "Aircraft Fuel Status and Communication Procedures" (PDF). Hong Kong Civil Aviation Department. Retrieved 13 June 2013.
- d.o.o, Spinaker. "DISTRESS alert (GMDSS)". egmdss.com.