NON-DSC Terrestrial Distress Communications

Effective communication is paramount during emergencies at sea. R/T (Radio Telephone) Distress procedures provide a standardized protocol for mariners to signal distress, relay alerts, and coordinate rescue efforts.

This article explores the various elements involved in R/T Distress Communications, ensuring you have the knowledge to act decisively in a critical situation.

DSC alerting in the GMDSS has been explained in article Digital Selective Calling (DSC): A Comprehensive Guide“Digital Selective Calling-DSC”. Non DSC terrestrial distress communications on MF, HF and VHF are described in this article.

R/T Distress Communications

The designated frequencies for distress, urgency and safety communications in the MF/HF and VHF bands are:

• 2182 kHz;
• 4125 kHz;
• 6215 kHz;
• 8291 kHz;
• 12290 kHz;
• 16420 kHz;
• 156.8 MHz – channel 16.

2182 kHz and VHF channel 16 are the two most likely to be used.

The radiotelephone distress procedure consists of:

• the alarm signal (whenever possible) followed by;
• the distress call;
• the distress message.

Two-Tone R/T Alarm Signal

The alarm signal is sent on 2182 kHz and comprises alternate tones of 1300 and 2200 Hz, each sent for 250 ms over a period of between 30 and 60 seconds.

The purpose of the signal is to:

1. Attract the attention of the person on watch.
2. Activate automatic alarm devices.
3. Activate a silenced or muted loudspeaker.

The alarm signal may only be used to announce:

1. That a distress call or message is about to follow.
2. The loss of persons overboard when the use of the urgency signal alone does not obtain assistance. The message should be preceded by the urgency signal.
3. By a coast station, to announce an urgent cyclone warning, the message being preceded by the safety signal.

The two-tone alarm should be used whenever possible before the distress call and message on 2182 kHz. It should be remembered that most ship stations use a muted loudspeaker 2182 kHz watch receiver, and nothing will be heard unless the mute is lifted. Some 2182 kHz watchkeeping receivers automatically lift the mute during silence periods.

R/T Distress Call

The distress call sent by radiotelephony consists of:

• The distress signal MAYDAY (×3);
• THIS IS (or DE, spoken as DELTA ECHO in case of language difficulties);
• CALL SIGN, NAME or other identification of the station in distress (×3).

The distress signal MAYDAY indicates that a ship, aircraft or other vehicle is threatened by grave and imminent danger and requires immediate assistance.

Distress Message

The message which follows the two-tone alarm (on 2182 kHz) and the call, must take the following form:

The same call and message formats would be used on any R/T distress frequency.

An example of a complete sequence of a distress transmission from vessel “WANDERER“, call sign “MMVR“:

(Two-Tone Alarm signal)

or

Further Information

“Any Other useful information” (some of which may be sent later if conditions permit) is:

1. Master’s intentions.
2. Type of cargo (if dangerous).
3. Weather and sea condition.
4. Time of abandonment.
5. Number and type of survival craft.
6. Number of persons abandoning/staying on board.
7. Details of location aids in survival craft or sea.

Distress Acknowledgement

A ship, upon receiving an R/T distress call and message from another ship which is, without doubt, in its vicinity should acknowledge receipt immediately unless it is in sea areas A1 or A2, when time should be given-for the coast station to acknowledge.

Where the station in distress is without doubt a long distance away, then acknowledge, and relay to the nearest coast station, only if no other acknowledgement has been heard.

In the case of an R/T distress call received on an HF distress frequency, remember that HF transmissions may be received at some locations but not at others (being in the skip zone, for example – see article Radio Wave Propagation – How it Works in the Shipping Industry“Exploring Radio Paths, Spectrum, and Propagation Mechanisms”). Therefore it should not be assumed either that a particular coast station has also received the distress alert or that the lack of an acknowledgement implies that none was sent.

The acknowledgement takes the following form:

Subsequent Communications

Every ship which acknowledges receipt of a distress message shall comply with Regulation 10 of SOLAS chapter V, as amplified by the MERSAR Manual. The master of a ship proceeding to the scene of a distress incident shall transmit, as soon as possible, the following information:

Note: Before transmission, the operator must ensure that no interference can be caused to stations which are in a better position to render assistance to the station in distress.

Mayday Relays

Stations NOT THEMSELVES in distress which learn that a ship, aircraft or other vehicle is in distress may transmit a distress relay message, but ONLY in the following circumstances:

a when the station in distress is not itself in a position to transmit the distress message;

b when the master or other person responsible for the station not in distress considers that further help is necessary;

c when, although not in a position to render assistance, the station has received a distress message which is believed not to have been acknowledged.

Such a distress relay, would normally be sent on 2182 kHz, channel 16 or any other R/T distress frequency, (see article Digital Selective Calling (DSC): A Comprehensive Guide“Digital Selective Calling-DSC” for the DSC distress relay procedure).

The distress relay call consists of:

This would then be followed by a repeat of the ORIGINAL DISTRESS MESSAGE.

Ships making a distress relay call should ensure that a suitable coast station is informed of the original distress communications.

If relaying specifically to a coast earth station, the Inmarsat terminal should be set to distress priority, i. e., level 3 (see article “Empowering Global Communication with INMARSAT Satellites in shippingINMARSAT SATELLITES“).

Note: NEVER substitute the name of the relaying station for that of the station in distress, even when identification is difficult. If the station in distress cannot he identified, it should he referred to as “Unidentified Trawler” or “Unidentified Helicopter“, for example.

Silence Periods

For 3 minutes, from each hour and each half-hour, all transmissions other than those for distress are forbidden in the band between 2173,5 and 2190,5 kHz. Operators must make a point of listening on 2182 kHz during these periods.

The NBDP and DSC distress frequencies 2174,5 kHz 2187,5 KHz are also inucled within this band.

The silence periods do not, however, apply to the DSC frequencies for intership/international shore-to-ship general calling, 2177 kHz, and international ship-to-shore general calling, 2189,5 kHz.

Time Signals

Time signals should be obtained daily to check the accuracy of the radio / bridge clock and the internal clocks within the various equipments. One reason for doing this is so that the silence periods are observed accurately. Standard time signal stations and their characteristics are listed in ITU List of Radiodetermination and Special Service Stations.

NBDP Distress Procedures

MF and HF frequencies are available for distress, urgency and safety traffic using NBDP, i. e.,

• 2174,5 kHz;
• 4177,5 kHz;
• 6268 kHz;
• 8376,5 kHz;
• 12520 kHz;
• 16695 kHz.

It is not intended that NBDP (radiotelex) be used as the primary method of distress alerting. It is more likely that it will be used to give “hard copy” during distress traffic following an alert or call on some other channel. The frequency 2174,5 kHz is most likely to be used for on-scene distress traffic.

All messages must be preceded by at least:

“carriage return” + “line feed” or “RETURN” (to advance paper) “letter shift” or “Caps lock”.

The distress signal MAYDAY

Forward error correction “FEC mode” should be used so that all stations can listen in, although “ARQ mode” may be used between two specific stations if necessary.

NBDP Acknowledgement

Acknowledgments to distress alerts and calls are normally made by ships using R/T in the same band as the original signal. NBDP techniques, however, could also be used, especially if no response was obtained on R/T.

The format will take the following form:

General search and rescue communications

Distress/SAR Traffic

Distress traffic consists of all messages relating to the immediate assistance required by a ship in distress, including search and on-scene communications. The control of traffic is initially the responsibility of the station in distress but is usually transferred, when, appropriate, to a properly equipped station such as a local coast station – normally the RCC (Rescue Co-ordination Centre) designated in the GMDSS Master Plan.

Radiotelephone Procedures During Distress Working

The distress signal MAYDAY should precede all distress traffic. The controlling station may impose silence on any interfering stations by using the term: SEELONCE MAYDAY.

Other stations may impose silence by using the term: SEELONCE DISTRESS

When complete silence is no longer necessary, the controlling station, may indicate that restricted working may be resumed by sending the following:

“PRUDONCE” means: Distress in force, but restricted working may be resumed.

When “normal working” may be resumed, the controlling station transmits a similar message but ends with:

“SEELONCE FEENEEY”

instead of:

“PRUDONCE”

NBDP Procedures During Distress Working

The controlling station may also impose silence on interfering stations by sending the radiotelex message:

SILENCE MAYDAY

Any other station may also impose silence, if it is necessary to do so, by using:

SILENCE DISTRESS

The NBDP message format used to indicate that “normal working” may be resumed is:

Supplementary Calling During Distress Working

In Regions 1 and 3, and in Greenland, the frequency 2191 kHz is used as a supplementary R/T calling frequency when 2182 kHz is being used for distress, with the coast station’s broadcast frequency being used for the reply. Both stations would then change to normal working channels.

In the United States, the frequency 4125 kHz is authorized for common use by coast stations and ship stations for R/T communications on a simplex basis provided that the power does not exceed 1 kW.

The frequencies 4123 kHz and 6215 kHz may also be used in simplex mode for general call and reply purposes by coast and ship stations provided that the power does not exceed 1 kW.

N. B. Since 4125 kHz and 621,3 kHz are both designated for use for distress and safety traffic, the use of these frequencies for other purposes is subject to the condition that no harmful interference shall be caused to distress, urgency and safety communications.

On Scene Co-ordination

In a distress or SAR situation it may be necessary for one of the participating stations to assume the role of On-scene Commander (OSC), and Co-ordinator Surface Search (CSS). If specialised SAR units (lifeboats, aircraft or war ships) are at the scene then one of those units should assume the role of OSC or CSS, or both. The duties of the OSC and CSS are many and varied; ship masters, mates and radio operators should therefore familiarize themselves with the IMO Merchant Ship Search and Rescue Manual (MERSAR).

On-Scene Communications

These are communications between the vessel in distress and other mobile units engaged in search and rescue. Control of on-scene communications is the responsibility of the OSC or the CSS, one duty being the nomination of the frequencies to be used. Simplex transmissions shall be used so that all information is shared. The preferred frequencies in radiotelephony for on-scene communications are channel 16 (156,8 MHz) and 2182 kHz.

Read also: GMDSS Distress and Safety Communications

The frequency 2174,5 kHz in the FEC mode may also be used for ship-to-ship on-scene communications using NSDP, especially in a hard copy printout is required.

Ship stations may communicate with aircraft stations for distress and safety purposes. In addition to channel 16 (156,8 MHz) and 9182 kHz, the following frequencies for on-scene communication between ships and aircraft may be used:

• 3023 kHz;
• 4125 kHz;
• 5680 kHz;
• channel 6.

The frequency 4125 kHz would normally be used in the first instance between SAR aircraft and ships. If contact on this frequency is not possible, aircraft will use 3023 kHz.

The aeronautical band frequencies 121,5 MHz and 123,1 MHz may also be used in mode of emission A3E; the former for the purposes of distress and urgency only, the latter for SAR operations.

Many organizations exist world-wide which are involved directly or indirectly in Search and Rescue (SAR) at sea.

As a backup to these organizations, all over the world a number of ship reporting systems are in use.

For example, in the English Channel a ship movement report system is in existence on VHF channel 16 (see ALRS Vol. 6 for details).

On a worldwide basis, the AMVER organization (Automated Mutual Assistance VEssel Rescue System), operated by the U. S. Coast Guard, provides aid to SAR efforts. AMVER started in 1958 as a computer-based search and rescue information system for the North Atlantic Ocean but has now grown into a world-wide safety network covering every ocean.

All vessels are encouraged to send details of their voyage and periodic position reports to the AMVER centre in New York via selected coast stations or via an Inmarsat CES. When a distress occurs, the AMVER computer can inform the relevant SAR authorities about which ships are in the area [see the ALRS Vol. 1 (i) for details].

The AMVER computer database relies on voluntary information provided by ships on their position and route. There are four types of report in the AMVER system, viz.

1. Sailing Plan, containing complete routeing information, which should be sent within a few hours of leaving port;
2. Position Report, sent within 24 hours of departure and updated at least every 48 hours until arrival in port;
3. Deviation Report, which should be sent whenever a material change to the planned route, affecting the accuracy of previously supplied information, occurs;
4. Arrival Report, which should be sent upon arrival in port.

The type of report is identified in the first line of the AMVER message, using the format:

AMVER/[report type]//

using the two-letter codes:

• SP (Sailing Plan),
• PR (Position Report),
• DR (Deviation Report),
• or FR (Arrival (Final) Report), e. g.,

AMVER/[report type]//

A standardised report format is used for the actual message, based on “report lines” in which letters of the alphabet are used to prefix and identify the type of information which follows. The “A” line, for example, identifies, by name and call sign, the ship sending the report, as in:

A/SEALAND MARINER/KGJF//

Discrete data elements, such as the vessel name and call sign above, are separated by a single slash (/) and the complete report line is terminated by a double slash (//).

There are fifteen types of report lines which may be used to construct AMVER messages. These are described in detail in the AMVER Ship Reporting System Manual.

It will interesting: TELEX (Narrow Band Direct Printing – NBDP) Procedures

The Japanese Ship Reporting System (CASREP) provides a parallel voluntary ship reporting service to AMVER around Japan. All vessels navigating in the JASREP service area are encouraged to participate.

Ships intending to participate in both JASREP and AMVER systems may send their reports to either one, since information may be exchanged between both systems upon request. The JASREP message follows very closely that of AMVER.

The Australian Ship Reporting System (AUSREP) is compulsory for Australian registered commercial vessels and for foreign vessels on voyages between Australian ports. For those ships participating in AUSREP, messages may be forwarded to AMVER upon request.

They are more report line possibilities in the AUSREP message structure, but otherwise the message format is very similar to that of AMVER.

Reports to AMVER, AUSREP and JASPEP are free of charge to the ship station concerned if sent via coast stations which have declared a no-charge arrangement.

However, the details of message structure, frequency of use and abatement of charges are subject to change.

Please refer to official sources for up-to-date information on operational details and charging rules.

Author

Olga Nesvetailova

Freelancer

Literature

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