Which radar observation most strongly suggests an imminent risk of collision with a moving target?

Which radar observation most strongly suggests an imminent risk of collision with a moving target?

• A. The target's range increases while bearing changes rapidly
• B. The target's bearing remains nearly constant while the range decreases
• C. The target disappears from radar
• D. The target's speed increases but bearing changes

Answer: (C)

The key idea is that the most urgent radar signal is losing track of a target you were watching. If a target disappears from your radar display, you can no longer judge its position or motion, so you have no reliable information about whether it’s on a collision course. That sudden loss creates a real, immediate danger because the other vessel could be very close or crossing into your path and you wouldn’t know where it is or where it’s going unless you quickly regain contact or switch to other means of detection. Action to regain/verify contact and, if needed, alter course or slow down should follow immediately. In comparison, a target that is closing with a nearly constant bearing does indicate a potential collision risk, but you still have a track to monitor and can coordinate avoidance. A target whose range is increasing while bearing changes rapidly is moving away or crossing out of your path, which is less alarming. A target that speeds up while bearing changes adds confusion but doesn’t by itself imply an imminent head-on threat as strongly as a loss of radar contact does.

The key idea is that the most urgent radar signal is losing track of a target you were watching. If a target disappears from your radar display, you can no longer judge its position or motion, so you have no reliable information about whether it’s on a collision course. That sudden loss creates a real, immediate danger because the other vessel could be very close or crossing into your path and you wouldn’t know where it is or where it’s going unless you quickly regain contact or switch to other means of detection. Action to regain/verify contact and, if needed, alter course or slow down should follow immediately.

In comparison, a target that is closing with a nearly constant bearing does indicate a potential collision risk, but you still have a track to monitor and can coordinate avoidance. A target whose range is increasing while bearing changes rapidly is moving away or crossing out of your path, which is less alarming. A target that speeds up while bearing changes adds confusion but doesn’t by itself imply an imminent head-on threat as strongly as a loss of radar contact does.