Mayday is an emergency code word used internationally as a distress signal in voice procedure radio communications. It derives from the French venez m'aider, meaning 'come help me'. It is used to signal a life-threatening emergency by many groups, such as police forces, pilots, the fire brigade, and transportation organizations. The call is always given three times in a row ("Mayday Mayday Mayday") to prevent mistaking it for some similar-sounding phrase under noisy conditions, and to distinguish an actual mayday call from a message about a mayday call. ''
Mayday calls can be made on any frequency, and when a mayday call is made no other radio traffic is permitted except to assist in the emergency. A mayday call may only be made when life or craft is in imminent danger of death or destruction.
'Mayday' calls are made by radio, such as a ship or aircraft's VHF radio. Although a Mayday call will be understood regardless of the radio frequency on which it is broadcast, first-line response organisations, such as the coastguard and air traffic control, monitor designated channels: marine MF on 2182 kHz; marine VHF radio channel 16 (156.8 MHz); and airband frequencies of 121.5 MHz and 243.0 MHz. A Mayday call is roughly equivalent of a morse code SOS, or a telephone call to the emergency services.
When they receive a Mayday call the coastguard may launch lifeboats and helicopters to assist the ship that is in trouble. Other ships that are nearby may divert course to assist the vessel broadcasting the Mayday.
Making a hoax Mayday call is a criminal act in many countries because of the danger to the rescuers' lives that a search-and-rescue operation can create, as well as the very high costs of such rescue efforts. For example, making a false distress call in the U.S. is a federal crime carrying sanctions of up to six years imprisonment, and a fine of $250,000.
The coastguard can be contacted in situations that are not emergencies (out of fuel, etc.) by calling 'Coastguard, Coastguard, Coastguard, this is (name of vessel)', on VHF channel 16. In many countries special training and a licence are required to use a mobile radio transmitter legally, although anyone may legally use one to summon help in a real emergency.
The recommended distress call format includes the word MAYDAY spoken three times (repeated twice), followed by the vessel's name or callsign, also spoken three times, then MAYDAY and the name or callsign again. Vital information, including the position, nature of the emergency, assistance required and the number of people on board, should follow. A typical message might be:
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. A Mayday can be sent on behalf of one vessel by another, using a convention called a Mayday Relay (see below).
The French "m'aider" translates as "to help me".
Mayday is one of a number of words used internationally as radio code words to signal important information. Senders of urgency calls are entitled to interrupt messages of lower priority. As with Mayday the use of these terms without proper cause could render the user liable to civil and/or criminal charges.
Each of these urgency calls is usually spoken three times (repeated twice); eg, "Pan-pan, Pan-pan, Pan-pan."
The following calls may be made only by the vessel in distress or the responding authority: