Mayday is the international radiotelephony distress signal for grave and imminent danger requiring immediate assistance. It opens a distress message carrying identity, position, the nature of the emergency and the assistance needed. In maritime and aviation radio, distress traffic takes priority over other communications. An isolated person can report an emergency this way when their remaining radio can reach a receiver operating in the appropriate radio service.
Mayday or Pan-Pan?
The actual danger determines the signal. A burning or sinking vessel, a life-threatening injury or an imminent forced landing may require immediate assistance. A technical fault alone does not describe that danger: a disabled boat in open water in calm weather faces a different situation from the same boat drifting towards a rocky shore. The message should therefore state the concrete consequence of the failure rather than merely name the fault.
Pan-Pan, spoken three times, announces an urgency message. It concerns the safety of a person or vehicle without describing the grave and imminent danger of a Mayday situation. Pan-Pan takes priority over routine traffic; Mayday also takes priority over urgency traffic. If conditions deteriorate into immediate grave danger, report the changed situation with Mayday so the receiver can recognise its increased severity.
Check the available radio link
A voice message needs an operational transmitter with power and an antenna, and a station able to receive its frequency and mode. Marine and aviation radios serve different radio services; the same channel number on unrelated sets does not identify a common transmission path. For VHF and the usual local aviation radio links, the radio horizon and obstructions limit reception. A low position, an antenna held close to the water or screening terrain can weaken the link. During evasion, gaining a better radio position also involves the risk of becoming visible while leaving concealment.
Listen briefly before transmitting to avoid overlapping an existing distress message. On a push-to-talk voice radio, press the transmit button before speaking clearly at normal volume. Release it at the end of the message and listen. Holding it down keeps this type of set in transmit mode and prevents reception of the reply. Shouting or rushing the message makes it harder to distinguish names, numbers and the actual assistance needed.
A usable maritime distress message
In maritime VHF radio, the spoken distress call is made on Channel 16. An available DSC controller can first send a digital distress alert on Channel 70. DSC means Digital Selective Calling: the set transmits a digital identity and, when suitable position data are available, the position. Channel 70 carries this digital traffic; it is not used for spoken messages. Voice communication then explains the actual emergency, the condition of the people involved and the assistance required. Activation follows the instructions for the particular set and its distress control.
The maritime message sequence can be organised as follows:
- Open distress traffic with “Mayday, Mayday, Mayday”.
- Say “This is”, repeat your vessel's name three times, then give its call sign or other identification and the available MMSI. The MMSI is the digital maritime radio identity.
- Say “Mayday” once, repeat your identification, then give the position.
- Describe the emergency, state the assistance required and report the number of people and any significant injuries or illnesses.
- Add information useful for the search, such as the vessel's appearance, its movement or an intention to abandon it. Finish with “Over” and switch to reception.
If only a few seconds remain, first transmit the distress signal, identity, a usable position and the immediate danger with the most important assistance needed. Additional details can follow when there is time to transmit again. A long account of events can crowd out the information that defines the search area.
Coordinates need complete values with an intelligible north/south and east/west designation. If only an estimated position or the last reliably known location is available, say so. A clearly named landmark with bearing and distance can provide a useful alternative. State where the direction starts and include the distance unit, for example: “The lighthouse bears 080 degrees magnetic from our position, distance two nautical miles.” State whether a bearing is true or magnetic. Add movement since that location or the vessel's drift. Invented precision sends the search to the wrong place.
In German sea areas, the coastal rescue radio station's call name is “Bremen Rescue”. The UK procedure likewise follows the digital alert with the spoken Mayday message on Channel 16. The distress signal remains internationally recognisable, while station names, radio networks and the physical reach of coastal stations vary locally. A radio indication that an alert has been sent initially describes the set's own transmission. An acknowledgement from another station is a separate return message.
What changes in aviation radio
In US aviation radio, an emergency is normally reported first to the air traffic facility on the frequency already in use. Mayday is followed by the station addressed, aircraft identity and type, and the actual emergency. Intentions and the assistance requested, position and heading, altitude, fuel remaining in minutes and the number of people provide information needed for further handling. If the current position is unknown, report the last known location, its time and the heading flown since then.
An unnecessary frequency change interrupts an established contact. If a change is necessary, tell the station the new frequency and the new station beforehand. If two-way contact cannot be established there, return to the last working connection. Marine channels and maritime DSC procedures do not form part of this aviation sequence.
An open distress call under hostile threat
An unencrypted voice call is intelligible to other compatible receivers. Speaking a position, injury and intended movement also discloses that information to potential hostile listeners; the transmission may also be used for radio direction finding. This relationship still applies to a military survival radio. In the US CSEL system, protected long-range data exchange is a separate function from unencrypted local voice communication.
For isolated personnel, this means using the communication path actually prepared and the radio instructions available, organising the necessary message beforehand and avoiding unnecessary repetition. An open Mayday call becomes especially relevant when immediate danger requires an attempt to alert a wider audience. Existing protected or specifically prepared links must be operated under their own procedures.
A name or call sign identifies the origin of a message. A replying voice alone does not establish that the station belongs to friendly forces. Contact with recovery forces still requires the prepared authentication procedure. Transmit the situation information needed for the actual contact; passwords and other protected identity information belong within the prescribed procedure.
After transmitting
After a reply, listen, ask for clarification of unclear instructions and correct information that has been misunderstood. Report changes in position, condition or intended action so the station works from the current situation. An acknowledgement means a station has received the message. The assistance it can actually arrange and when that assistance can reach the location must be established during further contact.
If a maritime call receives no answer, listen between brief repetitions. Check power, antenna, selected channel and mode against the instructions for the set. During military isolation, further transmissions and alternative links follow the radio instructions actually available. Calling indiscriminately on more channels consumes battery power and increases radio exposure while the location of any listening station remains unknown.