It is broadcast on one or a few MF/HF DSC frequencies by a person or vehicle in grave and imminent danger, and requiring immediate assistance.
A Distress alert transmits the following information:
  • The vessel’s MMSI
  • The vessel’s position (either from an interfaced GPS or manually entered by the operator)
  • The UTC time indicating the time when the latest position was updated
  • The nature of Distress (it remains undesignated in case of Undesignated Distress Alert)
  • Transmission frequency
  • Subsequent communication i.e. radiotelephone RT or radiotelex (NBDP/SITOR)
The vessel's position and UTC time (indicating the time when the latest position was updated) that are transmitted within a Distress Alert, is very important information for the rescue operation. So, if the MF/HF radio is not interfaced with GPS or automatic GPS, the entered position is invalid, and position and time should then be updated manually. The recommended minimum time period between updates is no more than 4 hours.

It is broadcast to ALL STATIONS and received by all within the MF or HF range of the station transmitting the alert.
It is expected that only a CRS will acknowledge the DSC Distress Alert by DSC and will act as the co-ordinator for the rescue, which would probably include other vessels in the vicinity. By answering a DSC distress call with DSC you are expected to act as the co-ordinator for the rescue. For that reason it will be a CRS that almost always acknowledges the Distress DSC.
Following on from the DSC Distress Alert, the station in distress will broadcast by voice or by telex on an associated frequency, a Distress Message. Always remember to write down what is said when the distress is broadcast by voice if you need to check some of the information later. Another thing to remember is that you are able to pick up Distress DSC messages from remote locations. So you should check the position of the station in distress against your position and determine if you are close enough and able to assist if needed.

MAYDAY, MAYDAY, MAYDAY
THIS IS (Name of the vessel in distress spoken 3 times)
(Call sign of the vessel in distress), (MMSI of the vessel in distress)
MAYDAY
(Name of the vessel in distress), (Call sign of the vessel in distress), (MMSI of the vessel in distress)
POSITION (Vessel's position) AT (Time of vessel's position in UTC)
(Type of accident)
IMMEDIATE ASSISTANCE REQUIRED
(Number of people onboard - Other information that could help SAR services such as weather conditions, activated EPIRB etc.)
OVER
Pattern of a Distress Call and Message

MAYDAY, MAYDAY, MAYDAY

THIS IS Sailboat Spinaker, Spinaker, Spinaker,
call sign Sierra 5 Lima 1 2, 278054321
MAYDAY
278054321, Spinaker, call sign Sierra 5 Lima 1 2
POSITION 450 36' North 0130 32' East AT 0545 UTC
The mast has broken and the engine is not strong enough to prevent us from grounding on a rocky shore
IMMEDIATE ASSISTANCE REQUIRED
5 persons on board and due to strong winds we can only remain on board for approximately two zero minutes
OVER
An example of a Distress Call and Message

A Distress Message must not begin with MAYDAY, MAYDAY, MAYDAY, if a Distress Call and Message has already been sent. A Distress message has to begin from MAYDAY in this situation.
There are three types of Distress Alert.

Undesignated Distress Alert

This is enabled either by pressing a single push button or a pair of push buttons, normally covered by a protective flap, for a short period of time, usually 5 seconds.
It is to be used only when there is no time to compose an alert because:
  • the position and time to be transmitted has not been checked and corrected so as to be up-to-date,
  • the alert will not include information relating to the nature of the distress (string "Undesignated" is sent).

Practise on the MF/HF radio simulator

  1. If necessary, switch on the DSC equipment by pressing the ON/OFF button.
  2. Lift up the lid covering the orange key and press down for 3 seconds.
  3. The distress will be accompanied by a sound.
  4. A Distress Message is sent using the continuous tone.
  5. Wait for distress acknowledgement and start mayday procedure. Unless stopped manually, by pressing the CANCEL soft key or switching the unit off, the distress call is automatically repeated every 3½-4½ minutes until distress acknowledgement is received.



Designated Distress Alert

This is enabled by programming the DSC Controller to include further information relating to the nature of distress and to update the time and position manually if necessary. The Designated Distress Alert is then broadcast by either pressing a single push button or a pair of push buttons for 5 seconds after programming.
The following are internationally recognized Natures of Distress:
  • Fire/Explosion
  • Flooding
  • Collision
  • Grounding
  • Listing/Capsizing
  • Sinking
  • Disabled & Adrift
  • Abandoning
  • Man overboard
  • Undesignated (same as an unprepared Undesignated Distress Alert)

Practise on the MF/HF radio simulator

  1. If necessary, switch on by pressing the ON/OFF button.
  2. Press the Menu button.
  3. Choose DSC CALL from SELECT MENU by using up and down softkeys.
  4. Press the OK softkey when the selected bar DSC CALL is lit.
  5. On the window named 'SELECT TYPE OF CALL' choose DISTRESS.
  6. On the next windows choose ALERT.
  7. On the window named SELECT NATURE OF DISTRESS choose the appropriate nature by using the up and down softkeys.
  8. On the window POS. AND TIME OF POSITION you can edit distress position and time by the CHANGE softkey and numerical soft keys. Set UNKNOWN when the distress position is unknown.
  9. Approve the settings by pressing the OK softkey.
  10. Lift up the lid covering the red DISTRESS button and press for 3 seconds.
  11. After that, DISTRESS CALL IS IN PROGRESS.
  12. After sending a DSC MF/HF distress call, the DSC receiver is AWAITING DSC ACKNOWLEDGEMENT.
  13. Retransmission of the DSC alert will be repeated every 3 ½ to 4 ½ minutes up until acknowledgement is received .



Mayday Relay (MF)

This is only broadcast when a station learns that:
  • Another person/vehicle is in Distress and is unable to transmit the Distress Alert itself, for example red flares sighted at night or
  • Distress Alert was not acknowledge by CRS, there is no subsequent communication on associated RT or telex frequencies and the DSC distress call is not continuing.
MAYDAY RELAY, MAYDAY RELAY, MAYDAY RELAY
THIS IS (Name of the vessel spoken 3 times), (Call sign of the vessel), (MMSI of the vessel),
RECEIVED THE FOLLOWING MAYDAY FROM (Name of the vessel in distress), (Call sign of the vessel in distress), (MMSI of the vessel in distress)
MESSAGE BEGINS
(message received from vessel in distress or details of the distress)
MESSAGE ENDS
OVER
Pattern of a Distress Relay Call and Message

MAYDAY RELAY, MAYDAY RELAY, MAYDAY RELAY

THIS IS Ferryboat Cathrine, Cathrine, Cathrine,
Sierra November Golf Charlie, 261431000
RECEIVED THE FOLLOWING MAYDAY FROM 278054321:
MAYDAY
Spinaker, call sign Sierra 5 Lima 1 2, 278054321,
POSITION 450 36' North 0130 32' East AT 0545 UTC
The mast has broken and the engine is not strong enough to prevent us from grounding on a rocky shore
IMMEDIATE ASSISTANCE REQUIRED
5 persons on board and due to strong winds we can only remain on board for approximately two zero minutes
OVER
An example of a Mayday Relay Call and Message

When a DSC Distress Alert is received by a CRS, there should be an immediate DSC acknowledgement from them. If the DSC Distress Alert goes unacknowledged, the DSC Controller will automatically repeat the broadcast at approximately 4 ½ minute intervals. A repeat broadcast can also be made manually by first cancelling the Distress Alert and re-programming the DSC Controller before once again pressing the Distress button(s) for 5 seconds. When a DSC Distress Alert acknowledgement is broadcast, this automatically stops the repeat of the Alert. The information contained in the acknowledgement includes:
  • MMSI of the acknowledging CRS,
  • Full Distress Call received from the station in Distress.
Any subsequent RT Distress Message broadcast on 2182 kHz will be acknowledged by voice by both the CRS and those vessels in the vicinity under the control of the CRS.

Distress Relay (HF)

This is only broadcast when a station learns that:
  • Another person/vehicle is in Distress and is unable to transmit the Distress Alert itself, for example red flares sighted at night or
  • Distress Alert was not acknowledge by CRS and there is no subsequent communication on associated RT or telex frequencies.
Note: Distress Relay Call must be addressed to CRS or RCC.

Practise on the MF/HF radio simulator



Reception of a Distress Alert (MF)

After receiving a Distress Alert on 2187.5 kHz, you must listen out for a Distress Message on an associated RT or telex frequency. Then wait for a CRS to acknowledge the call and for subsequent voice communication on an associated RT or telex frequency. If your own vessel is able to assist, acknowledge the call by using RT on 2182 kHz.
If a Distress Alert is not followed by an RT broadcast on 2182 kHz or acknowledged by any other station, acknowledge the call by RT on 2182 kHz and proceed with voice communication on 2182 kHz and try to notify the shore authorities by any means.

MAYDAY
(MMSI of the vessel in distress), (Name of the vessel in distress spoken 3 times), (Call sign of the vessel in distress)
THIS IS (MMSI of the vessel), (Name of the vessel spoken 3 times), (Call sign of the vessel)
RECEIVED MAYDAY
Pattern of acknowledgment of a Distress Call on RT

Practise on the MF/HF radio simulator



Reception of a Distress Alert (HF)

After receiving a Distress Alert on DSC, you must listen out for a Distress Message on an associated RT or telex frequency. Then wait for a CRS to acknowledge the call and for any subsequent voice communication on an associated RT or telex frequency. If your own vessel is able to assist, contact the RCC via the most efficient medium.
If a Distress Alert is not acknowledged by CRS and not followed up by RT or telex, transmit an addressed Distress Relay Call on DSC to CRS.

Practise on the MF/HF radio simulator


Control of communication on RT

During distress, silence on associated RT frequencies is automatically imposed. So, radio communication needs to be controlled. This control is achieved by all stations making a voice broadcast using some procedure words.
SEELONCE MAYDAY means that the frequency may only be used by the vessel in distress and the responding authority (and any other vessels which ask for assistance in handling the emergency). It is used by the responding authority when another vessel is interfering with distress communication.
SEELONCE DISTRESS means that the frequency may only be used by the vessel in distress and the responding authority (and any other vessels which ask for assistance in handling the emergency). It is used by any vessel when another vessel is interfering with distress communication.
PRUDONCE means that the frequency may also be used for restricted radio working. It is used by the responding authority when initial distress problems have been dealt with and it is expected that the distress won't be over soon.
SEELONCE FEENEE means that the distress is over and normal radio working can be resumed. In most cases it is used by a CRS.
All messages that control radio communication have the same pattern. Only different procedure words are used in different situations.

MAYDAY
ALL STATIONS, ALL STATIONS, ALL STATIONS
THIS IS (Name of the vessel or the responding authority spoken 3 times)
(Date and time in UTC)
(Name of the vessel in distress), (Call sign of the vessel in distress), (MMSI of the vessel in distress)
(procedure word)
OUT
Pattern of a Call and Message to control radio communication

MAYDAY

ALL STATIONS, ALL STATIONS, ALL STATIONS
THIS IS RCC KOPER, RCC KOPER, RCC KOPER
21 November at 0615 UTC
Spinaker, call sign Sierra 5 Lima 1 2, 278054321

SEELONCE FEENEE

OUT
An example of a Call and Message to announce that the distress is over

Cancelling a False Alert

If a DSC Distress Alert is broadcast in error, the Alert must be stopped from being repeated by either pressing a Cancel or Stop push button or by switching off the MF/HF DSC radio (though it should be switched back again on after a few seconds). An all-stations voice broadcast should then be made on an associated RT frequency, cancelling the alert and indicating that it was transmitted in error.

ALL STATIONS, ALL STATIONS, ALL STATIONS

THIS IS (Name of the vessel spoken 3 times), (Call sign of the vessel), (MMSI of the vessel),
POSITION (Vessel's position) AT (Time of vessel's position in UTC)

CANCEL MY DISTRESS ALERT OF (Original date and time of distress alert in UTC)

OVER
Pattern of a Call and Message to cancel a false Distress Alert

ALL STATIONS, ALL STATIONS, ALL STATIONS

THIS IS Spinaker, Spinaker, Spinaker, call sign Sierra 5 Lima 1 2, 278054321
POSITION 450 36' North 0130 32' East AT 0550 UTC

CANCEL MY DISTRESS ALERT OF 21 November at 0545 UTC

OVER
An example of a Call and Message to cancel a false Distress Alert