The Situation Report Message is used to send the equivalent information to AIS Message 1 but removes less essential data to compress message size.
Note: Only aircraft engaged in SAR (using SAR transponder) may transmit AIS.
This is an RTCM compliant update of the FID 0 Message 25 listed in the Oct 2014 EAIS IDD. It also replaces the DAC 366, FI 56 Position Report from the same document.
Encrypted Situation Report (Message 26, Broadcast)
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Parameter |
# of Bits |
Description |
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Standard Message Header |
Message ID |
6 |
Identifier for Message 26; always 26. |
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Repeat Indicator |
2 |
Indicates how many times a message has been repeated. 0 – 3; 0 = default; 3 = do not repeat any more. Set to zero (default). |
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Source MMSI |
30 |
MMSI number of source station. Varies according to the transmitter ID. |
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Destination Indicator |
1 |
0 = broadcast (no Destination ID field) 1 = Addressed (30 bit Destination ID field). Set to 1 (addressed). |
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Binary Data Flag |
1 |
0 = unstructured binary data (no Application Identifier bits used) 1 = binary data coded as defined by the 16-bit AI. Set to 1 (structured). |
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Destination ID |
0 |
MMSI number of destination station. Not Used. |
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Spare |
0 |
Not used. |
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Binary Data |
Designated Area Code |
10 |
Designated area code (DAC). Set to 366. |
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Function Identifier |
6 |
Function identifier. Set to (decimal) 38. |
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Encrypted Payload |
Version |
3 |
Sequential number used to indicate the message version in steps of 1. 0 = test message = default; 1 – 7 = message version. Set to zero. |
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Time of Position - UTC Min |
6 |
UTC Minute of the position. 0 – 59; 60 = UTC minute not available = default; 61 - 63 (reserved for future use). |
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Time of Position - UTC Sec |
3 |
UTC Seconds of the position; 10-second resolution. 0 = 0 sec; 1 =10 sec; 2 = 20 sec; 3 = 30 sec; 4 = 40 sec; 5 = 50 sec; 6 = unknown = default; 7 = (reserved for future use). |
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Craft Flag |
1 |
Indicates whether report is from a vessel or aircraft. 0 = vessel = default; 1 = aircraft. |
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Longitude |
28 |
Longitude in 1/10,000 min (±180 degrees, East = positive, West = negative. 181 degrees = not available = default). Negative in 2’s complement. |
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Latitude |
27 |
Latitude in 1/10,000 min (±90 degrees, North = positive, South = negative, 91 degrees = not available = default). Negative in 2’s complement. |
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Altitude |
12 |
Altitude above sea level in 1m increments. Set to 0 for vessels. 0-4,000 m; 4001 = 4,001 m or higher; 4,002 = unknown = default. |
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COG |
12 |
Course over ground in 1/10° increments. 0-359.9 degrees; 3,600 = not available = default; 3,601 – 4095 = reserved. |
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SOG |
10 |
Speed over ground. Scale dependent on value of craft flag. Aircraft: 0 – 1000 kts (1 kt increments); 1001 = 1001 kts or higher; 1002 = not available = default; 1003 – 1023 = reserved. |
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Operational Status |
4 |
Operational status of the craft reporting. 0 = unknown = default 1 = ops normal 2 = on scene as directed 3 = returning to port/land 4 = awaiting instructions 5 = Bravo at home port 6 = Bravo at port other than home 7 = Charlie, homeport 8 = Charlie, in repair 9-15 reserved. |
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Encryption Bit Padding |
22 |
Sufficient spare bits to ensure that the binary data is a multiple of 128 bits for block encryption. Set to 0. |
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Checksum |
16 |
16-bit CRC calculated as per EAIS Specification |
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Footer |
Spare |
4 |
Four extra bits to ensure the message ends on a byte boundary. Set to zero. |
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Communications State Selector |
1 |
0 = SOTDMA communication state follows 1 = ITDMA communication state follows |
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Communications State |
19 |
SOTDMA communication state (see ITU 1371-5 § 3.3.7.2.1, Annex 2), if communication state selector flag is set to 0, or ITDMA communication state (§ 3.3.7.3.2, Annex 2), if communication state selector flag is set to 1. |
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Total bits |
224 |
2 Slot Binary Message |
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