AIS message type
AIS message type 9: Standard SAR aircraft position report
Position, altitude, speed and course of a search-and-rescue aircraft. What type 9 carries, who sends it, how often, and how to read it.
What type 9 is
Type 9 is the aircraft equivalent of a position report. It adds a 12-bit altitude field in metres above the GNSS ellipsoid and reports speed in whole knots, because aircraft speeds do not fit the 0.1-knot resolution of a ship report.
How to read it
The sender's MMSI begins 111. Seeing a ship-looking dot at several thousand feet is not a bug: it is a helicopter or fixed-wing aircraft on a rescue task.
Field layout
Bit offsets are counted from zero at the first bit of the decoded payload.
| Bits | Field | Notes |
|---|---|---|
| 0–5 | Message type | |
| 6–7 | Repeat indicator | 0 = original, 1 to 3 = repeated by a repeater; 3 means do not repeat |
| 8–37 | MMSI | |
| 38–49 | Altitude | metres; 4095 = not available |
| 50–59 | Speed over ground | whole knots; 1023 = not available |
| 60 | Position accuracy | |
| 61–88 | Longitude | |
| 89–115 | Latitude | |
| 116–127 | Course over ground | |
| 128–133 | UTC second |
Paste a real sentence into the AIS message decoder to see these fields filled in.
All message types
| Type | Name |
|---|---|
| 1 | Position report, scheduled (Class A) |
| 2 | Position report, assigned schedule (Class A) |
| 3 | Position report, response to interrogation (Class A) |
| 4 | Base station report |
| 5 | Static and voyage related data (Class A) |
| 6 | Binary addressed message |
| 7 | Binary acknowledge |
| 8 | Binary broadcast message |
| 9 | Standard SAR aircraft position report |
| 10 | UTC and date inquiry |
| 11 | UTC and date response |
| 12 | Addressed safety related message |
| 13 | Safety related acknowledgement |
| 14 | Safety related broadcast message |
| 15 | Interrogation |
| 16 | Assignment mode command |
| 17 | DGNSS broadcast binary message |
| 18 | Standard Class B equipment position report |
| 19 | Extended Class B equipment position report |
| 20 | Data link management message |
| 21 | Aid-to-navigation report |
| 22 | Channel management |
| 23 | Group assignment command |
| 24 | Static data report (Class B) |
| 25 | Single slot binary message |
| 26 | Multiple slot binary message with communications state |
| 27 | Long-range AIS broadcast message |