Define CPA in ARPA terms and how it is used.

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Multiple Choice

Define CPA in ARPA terms and how it is used.

In ARPA terms, CPA is the closest point of approach: the minimum distance two vessels would have between them along their projected paths if both keep their current speed and course. This distance comes from extending each vessel’s track forward and finding where those tracks bring them closest together. CPA is used with TCPA (Time to Closest Point of Approach) to judge risk—if the CPA is small and the TCPA falls within a practical window, there’s a potential collision and action is needed. Remember, CPA is a distance predicted from current motion, not the current bearing, and it’s not the time to collision (that’s TCPA).

In ARPA terms, CPA is the closest point of approach: the minimum distance two vessels would have between them along their projected paths if both keep their current speed and course. This distance comes from extending each vessel’s track forward and finding where those tracks bring them closest together. CPA is used with TCPA (Time to Closest Point of Approach) to judge risk—if the CPA is small and the TCPA falls within a practical window, there’s a potential collision and action is needed. Remember, CPA is a distance predicted from current motion, not the current bearing, and it’s not the time to collision (that’s TCPA).

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