AIS Search and Rescue Transmitter (SART)
AIS search and rescue transmitters (SART) use the format 917203X4X5Y6Y7Y8Y9, where the digits 4 and 5 are assigned by the International Association for Marine Electronics Companies (CIRM) and refer to the SART manufacturer, and digits 6, 7, 8 and 9 are sequential digits assigned by the manufacturer identifying the SART.
Maritime Survivor Locating Devices (MSLDs) using DSC and AIS
The MSLD device that transmits DSC and/or AIS should use an identity 917223X4X5Y6Y7Y8Y9, (where xx = manufacturer ID 01 to 99 assigned by CIRM; yyyy = the sequence number 0000 to 9999. When reaching 9999 the manufacturer should restart the sequence numbering at 0000. The manufacturer ID xx = 00 is reserved for test purposes). Combination DSC - AIS devices will transmit one common user ID.
MSLD devices are described by standards RTCM 11901 and IEC 62329.
406 MHz EPIRB with AIS locating beacons
The EPIRB-AIS should use an identity 917243X4X5Y6Y7Y8Y9, (where xx = manufacturer ID 01 to 99; yyyy = the sequence number 0000 to 9999. When reaching 9999 the manufacturer should restart the sequence numbering at 0000.).
The user identity of the EPIRB-AIS indicates the identity of the homing device of the EPIRB-AIS, and not the MMSI of the ship.
406 MHz Personal Locator Beacons (PLBs) equipped with AIS locating beacons also use this identity.
Autonomous Maritime Radio Devices (AMRDs)
When implemented, AMRD Group B will describe AIS devices that transmit on 160.9 MHz, VHF channel 2006, and use the MMSI identity 917293Y4Y5Y6Y7Y8Y9. This MMSI is not transmitted on Channels AIS1 or AIS2. Y4Y5Y6Y7Y8Y9 is a pseudorandom number, to be determined by the manufacturer. AMRD Group B devices do not enhance the safety of navigation and they deliver signals or information which are not relevant for the navigator of general shipping. They are defined in more detail in Recommendation ITU-R M.2135.
AMRD Group A devices are used for safety purposes, transmitting on Channels AIS 1 and AIS 2, or Channel 70 DSC. They include the SART, MSLD, EPIRB described above, as well as the Mobile Aid to Navigation (see MMSIs for AIS Private Aids to Navigation).
Recognizing the differences in the 3-digit prefix for these three devices might be crucial in a Distress/SAR situation.
Note that MMSIs used by these devices are unregistered.