4 May 2021
Mayday is a radio distress call, a phonetic representation of the French m’aidez (help me). The phrase differs from S.O.S. in that S.O.S. is used in Morse code transmissions while mayday is used in voice transmissions.
The distress call was first adopted for use in cross-Channel flights from Britain to France in early 1923. Mention of it appears in a number of British newspapers, including the Times, on 2 February 1923:
New arrangements for the salving [sic] of aeroplanes that may be forced to alight in the Channel will be in operation during the forthcoming night flights between London and Paris. Owing to the difficulty of distinguishing the letter “S” by telephone, the international distress signal “S.O.S.” will give place to the words “May-day,” the phonetic equivalent of “M’aidez.” the French for “Help me.” During a recent test a R.A.F. flyingboat, descending in the Channel, gave the international distress signal three times by wireless telephony and reported that her engines had failed. The message was picked up at Croydon and Lympne. The Civil Aviation Traffic Officer at Lympne telephoned to the Dock Master at Dover, and within twenty minutes of the distress call a tug from Dover was alongside to give assistance, having steamed about three miles. No special warning had been given to Dover to be ready.
The distress call was adopted as the international standard by the 1927 International Radio Telegraph Convention held in Washington, D.C.
It’s often claimed that mayday was coined by Frederick Stanley Mockford, a radio operator at Croydon Airport in England. While plausible, this claim is undocumented.
Sources:
“New Air Distress Signal.” Times (London), 2 February 1923, 7. Gale Primary Sources: The Times Digital Archive.
Oxford English Dictionary, third edition, December 2020, s.v. Mayday, int. and n.2.
“Radio-Telephony on the London–Continental Air Routes.” Aeronautical Digest, 3.5, November 1923. 343. Gale Primary Sources: Smithsonian Collections Online.