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All questions
CPA

A relative plot forecasts a CPA of 1.0 M. What does CPA mean here?

Short answer

The shortest predicted separation if the observed relative motion continues

CPA is the perpendicular distance from own ship to the extended relative-motion line, conditional on the observed motion continuing. Revisit CPA and TCPA Worked Plot.

Quick check

A relative plot forecasts a CPA of 1.0 M. What does CPA mean here?