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GMDSS Distress and Safety Communications

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This paper investigates the technological infrastructure and the standardized communication protocols employed by the GMDSS distress calls and optimize search and rescue procedures.

We will explore the diverse communication technologies employed by the GMDSS, including VHF, MF, HF, and satellite-based systems like Emergency Position-Indicating Radio Beacons (EPIRBs).

GMDSS Distress Alerting

Distress and safety communications in the GMDSS rely on the use of radio communications through terrestrial MF, HF and VHF links and through satellites.

The transmission of a distress alert in the GMDSS indicates that a ship, aircraft or other vehicle or a person, is in distress and requires immediate assistance. Distress alerts in the GMDSS must provide the identification and position of the station in distress.

The distress alert consists of a Digital Selective Call, using a distress call format, in the bands used for terrestrial communications or a distress message format transmitted through a satellite system. The distress alert may only be sent on the authority of the master or other person responsible for the ship, aircraft or other vehicle carrying the radio station.

Ship-to-shore distress alerts in the GMDSS are used to alert RCCs via coast stations or coast earth stations that a ship is in distress and may use:

  • Digital Selective Calling (DSC) techniques in the MF, HF and VHF bands;
  • Inmarsat-A, –C or –B transmission;
  • EPIRB signal.

Ship-to-ship distress alerts in the GMDSS are used to alert ships in the vicinity of the ship in distress and are based on the use of DSC techniques in the VHF and MF bands. If warranted by circumstances, the HF bands may also be used.

DSC Distress Alerting

The terrestrial elements of the GMDSS are based on the use of Digital Selective Calling (DSC) for distress and safety communications. The DSC distress alert contains both the distress call and the distress message and provides for self-identification, ship’s position (including time) and the nature of distress. The detailed procedures for DSC distress and safety communications are described in article “Digital selective calling-DSC“.

Satellite Distress Alerting

Distress alerts sent through satellite systems operating in the GMDSS must use either general communication channels (i. e., Inmarsat-A, –B and –C) with absolute priority or exclusive distress and safety frequencies (i. e., EPIRBs).

The satellite systems providing distress alerting and communication facilities in the GMDSS, together with the detailed procedures for satellite distress, urgency and safety communications, are described in articles “INMARSAT SATELLITES” and “Maritime safety information (MSI)”.

Ship-to-shore distress alerts sent via satellite are routed immediately to an RCC, which then initiates a shore-to-ship distress alert relay.

EPIRB Distress Alerting

Distress alerts sent through an EPIRB (see article “EPIRBs and SARTs“) are notified by the system operator to an appropriate RCC, which then initiates a shore-to-ship distress alert relay.

Acknowledgement of Distress Alerts

The receipt of a distress alert or distress alert relay should be acknowledged receiving station at the earliest opportunity. The form of the acknowledgement shall be consistent with the detailed procedures applicable to the frequencies and techniques used to signal the distress.

In the GMDSS, coast stations and RCCs bear the primary coordinating the response to a distress alert and for organizing any subsequent search and Emergency operations and First aid on boardrescue operations.

A coast station or appropriate coast earth station which receives a distress alert must ensure that the information is routed as soon as possible to the appropriate RCC. The distress alert then has to be acknowledged as soon as possible by the coast station, or by the RCC through coast station or an appropriate coast earth station.

The acknowledgement indicates to the ship in distress and other stations, as appropriate, that the distress alert has been received and that the competent search and rescue authorities have been informed.

Role of Coast Stations and RCCs in the GMDSS

The preferred sequence of events in the GMDSS is that the DSC acknowledgement to a DSC distress call is transmitted by an appropriate coast station. This is because acknowledging by DSC has the effect of halting further transmissions of the DSC distress call from the station in distress.

The normal expectation would be that the RCC has been informed and it is safe for the DSC distress call to be terminated.

It will be interesting: GMDSS carriage requirements and basic provisions

The receiving station or the RCC must also analyse the circumstances of the distress alert in case there is a need to initiate the transmission of a shore-to-ship distress alert relay addressed, as appropriate, to all ships, to a selected group of ships or to a specific ship, by satellite or terrestrial means or by both.

A distress alert relay should normally be transmitted only when the method or frequencies, or both, used to transmit the original distress alert were such that ships in the area of the distress incident would otherwise be unaware of the plight of the station in distress.

The distress alert relay must contain the identification of the station in distress, its position and all other information that might assist rescue operations.

Role of Ship Station in the GMDSS

In ideal circumstances, ship stations should operate according to the directions of the coast station or RCC which has acknowledged the alert or transmitted a distress alert relay.

The immediate course of action to be take on board a ship which has received a distress alert or distress alert relay is to:

  • inform the master or other person responsible for the ship of the contents of the distress alert;
  • monitor the appropriate frequency for the follow up communications;
  • and prepare to acknowledge the distress alert by the appropriate means.

Ships which receive a DSC distress call will normally acknowledge by R/T (or NBDP, if indicated in the call) on the distress and safety traffic frequency in the same band in which the distress, call transmitted.

Acknowledgements by DSC should normally be sent only by appropriate coast stations. Only when it appears that a DSC distress alert has not been acknowledged by a coast station should a ship assume the responsibility to acknowledge by DSC or to make a distress alert relay.

Remember that the acknowledgment by DSC stops any further transmission of the DSC distress call from the station in distress. It is therefore essential that a ship station in receipt of a DSC distress call allows sufficient time for a coast station to send a DSC acknowledgement to the distress call before assuming the responsibility of acknowledging by DSC itself.

The general format for making the acknowledgement by R/T is:

the distress signal MAYDAY
 
the CALL SIGN or other IDENTIFICATION of the station sending the distress message (repeated 3 times)
 
THIS IS (or DE, spoken as DELTA ECHO in case of language difficulties)
 
the CALL SIGN or other IDENTIFICATION of the station acknowledging receipt (repeated 3 times)
 
RECEIVED (or RRR, spoken as ROMEO ROMEO ROMEO in case of language difficulties)
 
the distress signal MAYDAY

In those cases where NBDP/telex operation is to be used for subsequent communications during the distress incident, the general format for making the acknowledgement is:

MAYDAY
 
the CALL SIGN or other IDENTIFICATION of the station sending the distress message (repeated 3 times)
 
DE
 
the CALL SIGN or other IDENTIFICATION of the station acknowledging receipt (repeated 3 times)
 
RRR
 
MAYDAY

In the special case of receiving a DSC distress call only on the HF bands the ship station must not make any immediate acknowledgement but is required, in addition to maintaining a watch for a DSC acknowledgement from a coast station, to set watch on the most suitable R/T (or NBDP) HF distress and safety traffic frequency. The frequency guarded would be chosen from the bands on which the DSC distress call was received.

An alternative HF distress and safety traffic frequency should be selected if no distress traffic is received within 1 to 2 minutes. However, if no distress alert acknowledgement or other distress communication from a coast station is received within 3 minutes, then the ship station must relay the distress alert and inform an RCC by any appropriate means.

GMDSS Ships Receiving a 2 182 kHz/Ch. 16 R/T Distress Alert

In areas where are reliable communications with one or more coast stations, ship stations should defer acknowledgement of an R/T distress alert for a short interval in order to give time for the coast station to acknowledge the distress alert and to broadcast further instructions. This would usually be the case in sea areas A1 and A2.

However, in areas where reliable communications to a coast station are not practicable, a ship station which receives a distress alert from a ship definitely in its vicinity is obliged to acknowledge receipt as soon as possible and to relay the distress alert to an RCC through an appropriate coast station or coast earth station.

Urgency and Safety Communications

The GMDSS makes special provision for urgency and safety communications. Urgency messages concern the safety of a ship, aircraft, vehicle or person. In particular, communications related to obtaining medical advice may be accorded urgent status. Safety messages concern important meteorological or navigational information. The general procedures for urgency and safety communications, including medical transports and obtaining medical advice, are described further in articles “Digital selective calling-DSC” and “Terrestrial Urgency and Safety Communications”.

Search and Rescue Communications

The search and rescue communications and on-scene communications which take place while the rescue operation is in progress also count as distress traffic and may use GMDSS distress and safety frequencies. However, it is essential that good communications discipline is maintained throughout the duration of the distress incident.

Read also: Basic Concepts of the GMDSS

At different times during a distress incident, communications will be controlled by the RCC, the on-scene commander (i. e., a mobile unit co-ordinating search and rescue operations) or the coast station involved. The procedures to be used for general search and rescue and co-ordinating communications in the GMDSS are described in article “NON-DSC Terrestrial Distress Communications”.

Author
Author photo - Olga Nesvetailova
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Literature
  1. General operator’s Certificate for The Global Maritime Distress and Safety System, Course + Compendium, Model Course IMO 1.25, Printed by PMS UK Ltd London, 2004.
  2. European Radiocommunications Committee ERC Decision of 10 March 1999 on the harmonised examination syllabi for General Operator’s Certificate (GOC) and Restricted Operator’s Certificate (ROC)(ERC 99 01).
  3. IMO GMDSS-Handbook, London, U. K., 2004.
  4. Norcontrol Capella GMDSS Simulator, Technical documentations, Kongsberg Maritime Ship Systems, Norway, 2005.
  5. INMARSAT MARITIME COMMUNICATIONS HANDBOOK – INMARSAT – London, U. K, 2005.
  6. Seafarers’ Training, Certification and Watchkeeping CODE 1995 (STCW Code 95, published by IMO, London, 1996), – Part A Mandatory standards regarding provisions of the annex to the Convention Chapter IV Standards regarding radio personnel.
  7. Seafarers’ Training, Certification and Watchkeeping CODE 1995 (STCW Code 95, published by IMO, London, 1996), – Part B Mandatory guidance regarding provisions of the STCW and its annex; Chapter IV Guidance regarding radiocommunication and radio personnel.
  8. V. Pipirigeanu, M. Udrea, Introducere in GMDSS – Sistemul Mondial de Primejdie si Siguranta Maritima, Ed. Europolis, Constanta, 2002.
  9. Graham D. Lees, William G. Williamson, Handbook for Marine Radio Comunication, e d. LLOYD S OF LONDON PRESSLTD., 2004.
  10. ITU Manual for Use by The Maritime Mobile and Maritime Mobile Satellite Services, 2006.
  11. IAMSAR Manual – International Aeronautical and Maritime Search and Rescue Manual, 2001.
  12. C/S G.003 – Introduction to Cospas-Sarsat System, (G3OCT28.99D Issue 5 – Rev 1 October 1999), C/S Documents published by Cospas-Sarsat in Handbook of Regulations on 406 MHz and 121,5 MHz Beacons, (1999);
  13. Tor R. Kristensen – An Introduction to GMDSS, revised GOC Edition, – 7th edition, Leknes, Norway, 2007.
  14. C/S T.001 – Specification for Cospas-Sarsat 406 MHz Distress Beacon, (T1OCT30.99D – Issue 3-Rev. 2 October 1999), Documents published by Cospas-Sarsat in Handbook of Regulations on 406 MHz and 121,5 MHz Beacons (1999).
  15. IMO SOLAS (SAVE OF LIVE AT SEA), Consolidated Edition, London, 2001.

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