An unavailable AIS position report leaves no current location data, while a wrong one stems from faulty sensors because the system does not validate truth. USCG identifies Messages 1, 2 and 3 as Class A reports and Message 18 as the standard Class B report. An AIS position report carries dynamic data such as position, course, speed and navigational status, with the timestamp originating from the connected position sensor. Poorly configured or faulty sensors can transmit incorrect position information, and the built-in integrity test does not validate the truth of the sensor data. A target's AIS position is derived from its electronic position-fixing receiver and may not coincide exactly with the target detected by radar.
