GNSS Denied - The Position That Moved
Training scenario (fictional)
General cargo vessel · Approaches to a port (fictional) · Not applicable (training scenario)
Source: MGN 719
The Situation
FICTIONAL TRAINING SCENARIO, not a real incident. You are the officer of the watch at night, approaching restricted waters, when your position suddenly changes.
The Lesson
Verify GNSS against independent means, escalate early, and be ready to take the autopilot off track control.
Human Element
Interference shows up first as a disagreement between sensors. The decision that matters is whether the officer trusts one display or reconciles it with the others, and whether the response is sized to the waters.
Try the First Decision
Training scenario, not a real incident. You are the OOW on the 0000-0400 watch, approaching restricted waters, about 25 miles from the pilot station. In the space of a minute the ECDIS position jumps three miles and the SOG reading changes sharply. The radar picture, the log speed and the heading have not changed. AIS targets around you have scattered across the chart. What do you do first?
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