AIS signal loss means expected reports have stopped, requiring retained lookout and radar without treating absence as diagnosis.
When a graphical display no longer receives reports from a target within a preset distance, it may show a lost-target symbol at the latest known position. This visual cue indicates a break in data flow rather than a confirmed status of the vessel itself. The system might also detect its own malfunction through an integrity test alarm, causing the unit to stop transmitting or display a not-available value if a connected sensor fails.
Because not every vessel carries AIS and fitted equipment may be switched off in limited circumstances, the system does not present a complete traffic picture. The absence of an AIS target does not establish the absence of a vessel; lookout, radar and all other safety-relevant information remain necessary to maintain situational awareness.
