AIS dynamic data becomes unreliable when sensors fail or transmit incorrect values, requiring officers to maintain systematic visual and radar observation. A missing sensor may cause AIS to transmit a not-available value, while an inaccurate connected sensor may supply plausible but incorrect data that the built-in integrity test does not validate. Receiving a message does not prove that its values are accurate.
AIS dynamic data includes position with accuracy indications, UTC timestamp, course over ground, speed over ground, heading, navigational status, and rate of turn where available. However, navigational status is manually maintained rather than automatic, and update intervals vary by class, speed, and reporting mode. The officer of the watch must periodically check own-ship position, speed over ground, and sensor information to validate transmitted data accuracy.
AIS information should be corroborated through systematic visual and radar observation and must not replace lookout, radar plotting, or use of all available means. When dynamic data is missing or wrong, reliance on these traditional methods remains essential for safe navigation.
