87. DSC Alert Formats 87.1 The international DSC system provides for the following types of alerts: - distress alert - these calls are implicitly addressed to all stations. The alert contains the vessel’s MMSI, position information and its validity, and possibly an indication of the nature of the distress; - distress alert acknowledgement - normally only sent by Maritime Communication Stations and Limited Coast Stations in response to a distress alert. May be used by ship stations only under certain circumstances; - distress alert relay - normally only sent by Maritime Communication Stations and Limited Coast Stations. May be used by ship stations only under certain circumstances; - all stations (all ships) - used to alert all stations that an urgency or safety broadcast will follow and; - selective (single station) - used to alert a particular station to an urgency or safety message to follow. Some small vessel equipment may not permit the inclusion of the urgency or safety priority. This call is also used to alert another station to a routine call. The MMSI of the desired station must always be known and manually entered into the transceiver. The format of the MMSI indicates the type of station being called. 87.2 It is essential that operators of DSC-capable equipment are familiar with the particular alert options provided on the transceiver in use. It should be noted that the ‘all station’ format includes Maritime Communication Stations and Limited Coast Stations. Similarly the ‘selective’ format is used to address a particular Maritime Communication Station, Limited Coast Station or a ship station. 87.3 Some small vessel DSC-capable transceivers may not provide a distress alert relay format.
88. DSC Distress Alert Procedures 88.1 A distress alert from a vessel may be transmitted only on the authority of the master, skipper, or the person responsible for the safety of that vessel. It has absolute priority over all other transmissions and indicates that the vessel or person using it is threatened by grave and imminent danger and requests immediate assistance. All stations which receive a distress alert must immediately cease all transmissions capable of interfering with distress communications. 88.2 The distress alert should include the vessel’s last known position and an indication of when it was last updated. 88.3 Distress position information will normally be included automatically from an interface with satellite positioning equipment such as GPS. Some DSCs may permit position information to be inserted manually. Some DSCs may also offer the option of selecting from a menu and transmitting the nature of distress, for example, ‘on fire’, ‘collision’. 88.4 Once selected and initiated, a DSC distress alert will continue to be automatically repeated until terminated by the operator, or when a DSC distress alert acknowledgement generated by another station is received and decoded by the distressed vessel. 88.5 The DSC distress alert from a vessel is transmitted as follows: - select the appropriate MF/HF or VHF DSC controller; - select the appropriate distress option; - i.e. hold down the distress button or; - if time permits, edit the distress alert by keying in: - position information (not necessary with a GPS interface); - nature of distress (from the standard menu if provided); - mode for subsequent communications; either radiotelephony or telex. Choose radiotelephony; - select whether the alert will be transmitted on a single distress frequency or all the distress frequencies. The VHF DSC distress alert is transmitted on channel 70 only; - press the distress button to transmit the alert; - at the MF/HF or VHF transceiver, ensure the appropriate radiotelephony, distress frequency or VHF channel 16 is selected; - if time permits, the two tone radiotelephony alarm signal should be transmitted on the appropriate MF/HF radiotelephony distress frequency; - transmit the distress call and message as described in paragraphs 125 - 126 of this handbook. 88.6 Whilst these procedures may appear time-consuming, it is possible that all the vital information for the distress alert can be transmitted by a single button push. In a worst-case scenario where any further radio transmissions are not possible, the distressed vessel can be reasonably sure of having broadcast a distress alert containing its identity and its position.
AUSTRALIAN MARITIME COLLEGE
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