Navigation Center
United States Coast Guard
U.S. Department of Homeland Security

Long-range Automatic Identifcation System Broadcast Message (Message 27)

This message is primarily intended for long-range detection of AIS Class A and Class B “SO” equipped vessels (typically by satellite). This message has similar content to Messages 1, 2, and 3, but the total number of bits has been compressed to allow for increased propagation delays associated with long-range detection. Note there is no time stamp in this message. The receiving system is expected to provide the time stamp when this message is received.




Message ID 6 Identifier for this message; always 27
Repeat indicator 2 Always 3
User ID 30 MMSI number
Position accuracy 1 As defined for Message 1
RAIM flag 1 As defined for Message 1
Navigational status 4 As defined for Message 1
Longitude 18 Longitude in 1/10 min (±180°, East = positive (as per 2’s complement), West = negative (as per 2’s complement)

181° (1A838h) = position older than 6 hours or not available = default)

Latitude 17

Latitude in 1/10 min (±90°, North = positive (as per 2’s complement), South = negative (as per 2’s complement)

91° (D548h) = position older than 6 hours or not available = default)

Knots (0-62); 63 = not available = default


Degrees (0-359); 511 = not available = default

Position Latency 1

0 = Reported position latency is less than 5 seconds; 1 = Reported position latency is greater than 5 seconds = default

Spare 1

Set to zero, to preserve byte boundaries

Total Number of bits 96