Episode Details

In the early 1920s, Frederick Stanley Mockford, the officer in charge of radio at Croydon Airport in England, was asked to invent a spoken distress word that English and French crews on the Croydon to Le Bourget route could both understand. He chose mayday, a phonetic version of the French m'aider, from venez m'aider, come help me. Grammatically it is an infinitive, closer to shouting helping me than help me, but it cut through noise. SOS worked well in Morse code, yet the hissing sibilant S vanished into the static of AM voice radio and biplane ignition noise, while the voiced M and D and open vowels of mayday punched through. The 1927 International Radiotelegraph Convention in Washington adopted mayday as the radiotelephone distress call alongside SOS.

The episode then walks through the protocol built around the word: saying it three times, and the FAA list of station, call sign, aircraft type, emergency, weather, intentions, position, altitude, fuel in minutes, and souls on board. Fuel in minutes tells rescuers how long the aircraft can stay up and how much fire risk to plan for. Pan-pan, from the French panne for breakdown, signals urgency short of grave danger. Controllers impose radio silence with seelonce mayday and end it with seelonce fini, and ICAO warns against plain phrases like declaring emergency because they force controllers to interpret.

• Making a false distress call is a federal crime in the United States.
• A station that hears a vessel unable to transmit can send a mayday relay on its behalf.
• Pan-pan medico was once used to flag medical transports but is no longer in official use.
• In 1998 the crew of Swissair Flight 111 upgraded from pan-pan by radioing that they were declaring emergency.
• Older terms such as seelonce distress and prudence were retired in 2007.