Which condition triggers an alarm related to position sources?

• A. A mismatch between primary position and the compass
• B. The AIS target moves outside a permitted area
• C. The vessel's speed exceeds a threshold
• D. Your primary and secondary position source exceeds a set distance

Answer: (D)

The important idea is monitoring position source integrity by comparing multiple position estimates and raising an alarm when they disagree beyond a set limit. In integrated navigation, you typically rely on a primary position source (like GNSS) and a secondary source (such as an inertial/navigation aid or another independent sensor). The system continuously checks how far apart these two estimated positions are. If the divergence exceeds the predefined distance, an alarm is triggered to alert you to a possible sensor fault, spoofing, or degraded navigation accuracy. This criterion directly matches the scenario where the primary and secondary position sources exceed a set distance, which is why it’s the correct condition.

The other situations correspond to different alarms: a mismatch between position and compass signals a cross-check issue between position and heading; an AIS target moving outside a permitted area is about target tracking or security alerts; and a speed breach triggers a velocity-related alert.