Recommendation 541-8 a1

Recommendation 541-8

(1978-1982-1986-1990-1992-1994-1995-1996-1997)

OPERATIONAL PROCEDURES FOR THE USE OF DIGITAL SELECTIVE-CALLING EQUIPMENT IN THE MARITIME MOBILE SERVICE

(Question ITU-R 9/8)

ANNEX 1
Provisions and procedures for distress and safety calls

1 Introduction
The terrestrial elements of the GMDSS adopted by the 1988 Amendments to the International Convention for SOLAS, 1974, are based on the use of DSC for distress and safety communications.
1.1 Method of calling
The provisions of Chapter NIX (SVII) are applicable to the use of DSC in cases of distress, urgency or safety.
2 DSC distress call and message
The DSC "distress call" provides for alerting, self-identification, ship's position including time, nature of distress and contains both the distress call (RR No.3091 and 3092 (Appendix S13, Part AS. з 4)) and the distress message (RR No. 3093 and 3094 (Appendix S13, Part A3, з 5)) as defined in the RR.
3 Procedures for DSC distress calls
3.1 Transmission by a mobile unit in distress
3.1.1 The DSC equipment should be capable of being preset to transmit the distress call on at least one distress alerting frequency. 3.1.2 The distress call shall be composed in accordance with Recommendation ITU-R M.493; the ship's position information, the time at which it was taken and the nature of distress should be entered as appropriate. If the position of the ship cannot be entered, then the position information signals shall be transmitted automatically as the digit 9 repeated ten times. If the time cannot be included, then the time information signals shall be transmitted automatically as the digit 8 repeated four times.
3.1.3 Distress call attempt at MF and HF a distress call attempt may be transmitted as a single frequency or a multi-frequency call attempt. At VHF only single frequency call attempts are used.
3.1.3.1 Single frequency call attempt A distress call attempt should be transmitted as 5 consecutive calls on one frequency. To avoid call collision and the loss of acknowledgements, this call attempt may be transmitted on the same frequency again after a random delay of between 3_1/2 and 4_1/2 min from the beginning of the initial call. This allows acknowledgements arriving randomly to be received without being blocked by retransmission. The random delay should be generated automatically for each repeated transmission, however it should be possible to override the automatic repeat manually.
At MF and HF, single frequency call attempts may be repeated on different frequencies after a random delay of between 3? and 4? min from the beginning of the initial call. However, if a station is capable of receiving acknowledgement continuously on all distress frequencies except for the transmit frequency in use, then single frequency call attempts may be repeated on different frequencies without this delay.
3.1.3.2 Multi-frequency call attempt A distress call attempt may he transmitted as up to 6 consecutive (see Note 1) calls dispersed over a maximum of 6 distress frequencies (1 at MF and 5 at HF). Stations transmitting multi-frequency distress call attempts should be able to receive acknowledgements continuously on all frequencies except for the transmit frequency in use, or be able to complete the call attempt within 1 min. Multi-frequency call attempts may be repeated after a random delay of between 3_1/2 and 4_1/2 min from the beginning of the previous call attempt.
NOTE 1 - A VHF call may be transmitted simultaneously with an MF/HF call.
3.1.4 Distress In the case of distress the operator should:
3.1.4.1 enter the desired mode of the subsequent communication and if time permits, enter the ship's position and time (see Note 1) it was taken and the nature of distress (see Note 1);
NOTE 1 If these are not provided automatically.
3.1.4.2 select the distress frequency(ies) to be used (see Note 1 of з3.1.4.1);
3.1.4.3 activate the "distress call" attempt by a dedicated distress button.
3.1.5 Cancellation of an inadvertent distress call
A station transmitting an inadvertent distress call shall immediately cancel the alert over each channel on which the distress call was transmitted. For this purpose, a "distress cancellation" call in the format indicated in Recommendation ITU-R M.493, Fig. 4c) may be transmitted with own ship's maritime mobile service identity (MMSI) inserted as identification of ship in distress.
This distress cancellation should be followed immediately by the voice cancellation procedure as described in Annex 3(з1.7).
3.2 Reception
The DSC equipment should be capable of maintaining a reliable watch on a 24-hour basis on appropriate DSC distress alerting frequencies.
3.3 Acknowledgement of distress calls
Acknowledgements of distress calls should be initiated manually. Acknowledgements should be transmitted on the same frequency as the distress call was received.
3.3.1 Distress calls should normally be acknowledged by DSC only by appropriate coast stations. Coast stations should, in addition, set watch on radiotelephony and, if the "mode of subsequent communication" signal in the received distress call indicates teleprinter, also on narrow-band direct-printing (NBDP) (see Recommendation ITU-R M.493). In both cases, the radiotelephone and NBDP frequencies should be those associated with the frequency on which the distress call was received.
3.3.2 Acknowledgements by coast stations of DSC distress calls transmitted on MF or HF should be initiated with a minimum delay of 1 min after receipt of a distress call, and normally within a maximum delay of 2_3/4 min. This allows all calls within a single frequency or multi-frequency call attempt to he completed and should allow sufficient time for coast stations to respond to the distress call. Acknowledgements by coast stations on VHF should be transmitted as soon as practicable.
3.3.3 The acknowledgement of a distress call consists of a single DSC acknowledgement call which should be addressed to "all ships" and include the identification (see Recommendation ITU-R M.493) of the ship whose distress call is being acknowledged.
3.3.4 Ship stations should, on receipt of a distress call, set watch on an associated radiotelephone distress and safety traffic frequency and acknowledge the call by radiotelephony. If a ship station continues to receive a DSC distress call on an MF or VHF channel, a DSC acknowledgement should be transmitted to terminate the call and should inform a coast station or coast earth station by any practicable means.
3.3.5 The automatic repetition of a distress call attempt should be terminated automatically on receipt of a DSC distress acknowledgement.
3.3.6 When distress and safety traffic cannot be successfully conducted using radiotelephony, an affected station may indicate its intention (using an "all ships" DSC call, with the category distress, and normally indicating the frequency of the associated NBDP channel) to conduct subsequent communications on the associated frequency for NBDP telegraphy.
3.4 Distress relays
Distress relay calls should be initiated manually.
3.4.1 A distress relay call should use the telecommand signal "distress relay" in accordance with Recommendation ITU-R M.493 and the calling attempt should follow the procedures described in з3.1.3 to 3.1.3.2 for distress calls.
3.4.2 Any ship, receiving a distress call on an HF channel which is not acknowledged by a coast station within 5 min, should transmit a distress relay call to the appropriate coast station.
3.4.3 Distress relay calls transmitted by coast stations, or by ship stations addressed to "all ships", should be acknowledged by ship stations using radiotelephony. Distress relay calls transmitted by ships should be acknowledged by a coast station transmitting a "distress relay acknowledgement" call in accordance with the procedures for distress acknowledgements given in з 3.3 to 3.3.3.
4 Procedures for DSC urgency and safety calls (see Note 1)
4.1 DSC, on the distress and safety calling frequencies, should be used by coast stations to advise shipping, and by ships to advise coast stations and/or ship stations, of the impending transmission of urgency, vital navigational and safety messages, except where the transmissions take place at routine times. The call should indicate the working frequency which will be used for the subsequent transmission of an urgent, vital navigational or safety message.
4.2 The announcement and identification of medical transports should be carried out by DSC techniques, using appropriate distress and safety calling frequencies. Such calls should use the category "urgency", and telecommand "medical transport" and be addressed to "all ships".
4.3 The operational procedures for urgency and safety calls should be in accordance with the relevant parts of Annex 2, з 2.1 or 2.2.
NOTE 1 - Use of the DSC distress and safety calling frequencies for urgency and safety calls is acceptable, technically, provided that the total channel loading is maintained below 0.1 E.
5 Testing the equipment used for distress and safety calls
Testing on the exclusive DSC distress and safety calling frequencies should be avoided as far as possible by using other methods. There should be no test transmissions on the DSC calling channel on VHF. However, when testing on the exclusive DSC distress and safety calling frequencies on MF and HF is unavoidable, it should be indicated that these are test transmissions (see RR No. N 3068 (S31.3)). The test call should be composed in accordance with Recommendation ITU-R M.493 (see Table 6) and the call should be acknowledged by the called coast station. Normally there would be no further communication between the two stations involved.

Radio Officer й 2002 Edition