Short answer: The internationally recognised distress signals are listed in Annex IV of the International Regulations for Preventing Collisions at Sea (COLREG). There are 15 of them. They include MAYDAY by radio, SOS in Morse code, red parachute and hand flares, orange smoke, the NC flags, a square flag with a ball, a continuous fog-horn sound, a gun fired about once a minute, flames on the vessel and slowly raising and lowering outstretched arms. The list also covers DSC and satellite distress alerts, EPIRB signals and other approved radio signals such as a SART. Using any of them except in distress is prohibited.
What Is a Distress Signal?
A distress signal tells others that a vessel or person is in grave and imminent danger and needs immediate help. It is the highest priority call at sea and starts a search and rescue response.
Radio calls use three levels of priority, which are often confused:
| Call | Meaning | Example |
|---|---|---|
| MAYDAY | Distress: grave and imminent danger, immediate help needed | Fire out of control, sinking, a person overboard who cannot be recovered |
| PAN-PAN | Urgency: an urgent message about the safety of a vessel or person, without grave and imminent danger | Engine failure needing urgent assistance in open water, a medical problem needing advice |
| SÉCURITÉ | Safety: navigation or weather safety information | A floating hazard, a gale warning |
If a situation could become grave and imminent, such as an engine failure while drifting towards rocks, do not delay a MAYDAY.
The 15 International Distress Signals (COLREG Annex IV)
COLREG Annex IV lists the following signals, which may be used together or separately to show distress and need of assistance:
| # | Signal | Type |
|---|---|---|
| (a) | A gun or other explosive signal fired at intervals of about a minute | Sound |
| (b) | A continuous sounding with any fog-signalling apparatus | Sound |
| (c) | Rockets or shells throwing red stars, fired one at a time at short intervals | Visual |
| (d) | SOS (···−−−···) in Morse code by any signalling method | Visual, sound or radio |
| (e) | The spoken word “MAYDAY” by radiotelephony | Radio |
| (f) | The International Code signal of distress, the flags N and C | Visual |
| (g) | A square flag with a ball, or anything resembling a ball, above or below it | Visual |
| (h) | Flames on the vessel, as from a burning tar barrel or oil barrel | Visual |
| (i) | A rocket parachute flare or a hand flare showing a red light | Visual |
| (j) | A smoke signal giving off orange-coloured smoke | Visual |
| (k) | Slowly and repeatedly raising and lowering arms outstretched to each side | Visual |
| (l) | A digital selective calling (DSC) distress alert on VHF channel 70, or on MF/HF 2187.5, 4207.5, 6312, 8414.5, 12577 or 16804.5 kHz | Radio |
| (m) | A ship-to-shore distress alert sent by the ship’s Inmarsat or other mobile satellite service ship earth station | Satellite |
| (n) | Signals transmitted by an emergency position-indicating radio beacon (EPIRB) | Satellite |
| (o) | Approved signals transmitted by radiocommunication systems, including survival craft radar transponders (SART) | Radio |
Annex IV also draws attention to two aids that help rescuers find a vessel, especially from the air: a piece of orange canvas with a black square and circle or another appropriate symbol, and a dye marker. Using any distress signal, or any signal that could be confused with one, except to indicate distress is prohibited.
Illustration: a red parachute flare, a red hand flare and orange smoke are all Annex IV distress signals.
How Many Distress Signals Are There?
COLREG Annex IV lists 15 distress signals, (a) to (o). Lists of 16 or 17 usually add the orange canvas and the dye marker from paragraph 3. Older lists may also include radio alarm signals that were removed by amendments adopted in 2007 (Resolution A.1004(25)), which entered into force on 1 December 2009.
There is no official list of “5 distress signals”. Short lists like that are a selection of the most common ones, for example MAYDAY by radio, a DSC or EPIRB alert, red flares, orange smoke and a continuous fog horn.
Which of These Is Not a Distress Signal?
White flares and the single flag V are not Annex IV distress signals. Other signals often mistaken for distress signals are:
- The single flag V means “I require assistance”. It asks for help but is not a distress signal under Annex IV. The flag distress signal is N and C together.
- White flares are used to show your presence and avoid a collision. They are not distress signals.
- Short or prolonged horn blasts in a pattern are manoeuvring and warning signals. Only a continuous sound on a fog-signalling device is a distress signal.
- A high-intensity white light flashing regularly 50 to 70 times a minute is an additional distress signal recognised only under the US Inland Navigation Rules; it is not in the international list.
How to Send a Mayday
A maritime distress call is fastest when a DSC alert is followed by a voice MAYDAY:
- Send the DSC alert. On a DSC VHF radio programmed with the vessel’s MMSI, lift the cover and press and hold the distress button for the time the manufacturer specifies (often about five seconds) until the radio confirms the alert. Check that the radio has the yacht’s current position.
- Make the voice call on VHF channel 16:
- “MAYDAY, MAYDAY, MAYDAY”
- “This is [vessel name] ×3, call sign and MMSI”
- “MAYDAY [vessel name], call sign and MMSI”
- Position
- Nature of distress
- Assistance required
- Number of people on board
- Any other useful information (for example, “abandoning to liferaft”)
- “OVER”
- Stay on channel 16 and repeat the call if there is no answer.
The nature of distress is a one-line statement of what is wrong, such as fire, flooding, sinking, collision, grounding or person overboard, so that rescuers know what help to send.
VHF DSC works within VHF radio range. Beyond that, a 406 MHz beacon or satellite communication is needed to raise the alarm.
If you send a VHF DSC distress alert by mistake, cancel it at once: follow the radio’s cancellation procedure, then call “All stations, all stations, all stations” on channel 16 with the vessel’s name, call sign, MMSI and position, and say “Cancel my distress alert of [date, time UTC]”.
EPIRB and PLB: What They Are and How They Work
An EPIRB (emergency position-indicating radio beacon) is a distress beacon for a vessel. A PLB (personal locator beacon) is a smaller beacon carried by a person. Both transmit a distress alert on 406 MHz to the Cospas-Sarsat satellite system, which passes it to a rescue coordination centre. Both usually also transmit a 121.5 MHz homing signal that rescuers use to find the beacon at close range, and some models also broadcast an AIS signal.
| EPIRB | PLB | |
|---|---|---|
| Carried by | The vessel | A person |
| Registration | Vessel details | Personal user details |
| Activation | Category I: float-free with automatic or manual activation; Category II: manual | Manual |
| Use | Abandoning ship, sinking, any distress at sea | Person overboard, liferaft, a lone crew member |
Register every beacon in the register of the country whose code it is programmed with. Registration links the alert to the vessel or person and to emergency contacts, which helps rescuers respond. See the glossary entries for EPIRB, PLB and GMDSS.
Illustration: electronic alerting and visual signals work together.
Visual Distress Signals: Flares and Smoke
Visual distress signals help rescuers find you once the alarm has been raised. Each type has a different job:
- Red parachute rockets climb high and attract attention at a distance, especially at night or offshore.
- Red hand flares pinpoint your position when rescuers are close.
- Orange smoke marks your position by day, especially for aircraft, and shows the wind direction.
How far a flare can be seen depends on the product, the weather, visibility and the height of the observer, so treat published distances as a guide only.
Use pyrotechnics safely. Read each device’s instructions before an emergency and follow them. Keep flares away from sails and rigging, hold hand flares at arm’s length over the side, and never launch a parachute rocket when a helicopter is nearby. Keep gloves and eye protection with the flare kit. Check expiry dates: in the United States, for example, approved pyrotechnic signals are marked with an end of service life no more than 42 months from manufacture. Dispose of expired flares only through approved channels, never in household waste.
What Distress Equipment Should a Yacht Carry?
Carriage requirements depend on the yacht’s flag, size, use and operating area. Commercial yachts follow their flag’s yacht code and life-saving appliance rules, which draw on the IMO LSA Code. Private yachts are often less regulated. In the UK, for example, pleasure vessels under 13.7 m are not legally required to carry life-saving appliances such as flares. Carrying suitable distress alerting and locating equipment is still strongly recommended.
A practical approach for any yacht is to combine:
- Distress alerting: a DSC VHF radio for alerts within VHF range, and a 406 MHz EPIRB or satellite communication for alerts beyond it
- Locating aids for the final approach: flares, orange smoke, a handheld VHF, and a SART or AIS-SART where carried
- Personal beacons: PLBs for crew working on deck or in exposed conditions
Distress Signals and the GMDSS
The Global Maritime Distress and Safety System (GMDSS) is the international system that links ships, satellites and shore stations so that distress alerts reach rescue coordination centres. GMDSS carriage requirements depend on the applicable SOLAS and flag-state rules and on the sea area the vessel operates in. Typical GMDSS equipment includes VHF DSC, MF/HF radio, satellite terminals, EPIRBs, SARTs and NAVTEX. Electronic alerting raises the alarm; visual and sound signals help rescuers find you at close range.
Distress Equipment in a Refit
A refit that changes the bridge, antennas, cabling or safety equipment can affect how the distress alerting chain works. The owner’s team and the surveyor should confirm that the system still works as a whole: antenna positions, GPS feeds to DSC radios, the EPIRB bracket and hydrostatic release location, and updated beacon registration. See fire and safety and electrical and electronic systems.
Frequently Asked Questions
What are the international distress signals?
They are the 15 signals listed in COLREG Annex IV. They include MAYDAY by radio, SOS, red flares and rockets, orange smoke, the NC flags, a square flag with a ball, a continuous fog horn, a gun fired about once a minute, flames on the vessel, raising and lowering outstretched arms, DSC and satellite distress alerts, EPIRB signals and other approved radio signals such as SART.
How many distress signals are there?
COLREG Annex IV lists 15. Lists of 16 or 17 usually add the orange canvas and the dye marker, or older radio alarm signals that are no longer in the list.
Which of the following is a recognised distress signal?
Any signal in COLREG Annex IV, such as a red hand flare, orange smoke, MAYDAY or a continuous fog horn. White flares, the single V flag and horn blasts in a pattern are not distress signals.
What is a maritime distress call?
It is the voice call MAYDAY, made on VHF channel 16 or the MF distress frequency 2182 kHz and usually preceded by a DSC distress alert, when a vessel or person is in grave and imminent danger.
What is the Mayday flag?
There is no single “Mayday flag”. The International Code flag signal for distress is N over C. A square flag with a ball, or something resembling a ball, above or below it is also a recognised distress signal.
What is the difference between Mayday and Pan-Pan?
MAYDAY is a distress call for grave and imminent danger needing immediate help. PAN-PAN is an urgency call about the safety of a vessel or person when the danger is not grave and imminent.
What does EPIRB mean?
EPIRB stands for emergency position-indicating radio beacon. It sends a 406 MHz distress alert with the vessel’s identity, and usually its position, to rescue authorities through the Cospas-Sarsat satellite system.
What is the difference between an EPIRB and a PLB?
An EPIRB is carried by and registered to a vessel and can be float-free and automatic. A PLB is smaller, carried by a person, registered to that person and activated manually. Both transmit on 406 MHz.
Can I use a PLB instead of an EPIRB on my yacht?
Not where an EPIRB is required. A PLB is registered to a person, is not float-free and activates only manually, so it does not meet a vessel EPIRB carriage requirement. Many yachts carry both.
Are flares still needed if I have an EPIRB and DSC?
Often, yes. Electronic alerts raise the alarm, but flares and smoke help rescuers find you at the end, especially at night or in poor visibility. Check your flag and local rules.
What happens after I activate an EPIRB?
Satellites detect the 406 MHz signal and pass it to a mission control centre, which sends it to the responsible rescue coordination centre. The centre assesses the alert, checks the registration and coordinates an appropriate response, using the beacon’s position and homing signal. Keep the beacon on and upright with a clear view of the sky.
What should I check on my yacht’s distress equipment before a passage?
Check four things:
- Beacons are registered and within their battery and service dates, and the EPIRB’s hydrostatic release is in date.
- DSC radios have the MMSI programmed and receive a position.
- Flares are in date and easy to reach.
- Everyone on board knows how to send a MAYDAY and activate the beacons.
How do I dispose of expired flares?
Never put them in household waste. Use your coast guard, local authority or an approved disposal point, and plan disposal when you replace your flares.
Sources
- USCG Navigation Center: Annex IV, international distress signals
- IMO Resolution A.1004(25): amendments to COLREG Annex IV
- IMO: Preventing collisions at sea (COLREG)
- International Code of Signals (Pub. 102, 2020 edition)
- USCG Navigation Center: GMDSS frequently asked questions
- USCG Navigation Center: Cancelling a false distress alert
- IMO: Radiocommunications and GMDSS
- NOAA SARSAT: 406 MHz emergency beacons
- MCA MGN 599 (Amendment 1): pleasure vessels regulations and exemptions
- 46 CFR (2023): pyrotechnic distress signal approval requirements
