What do CPA and TCPA stand for, and how are they used?

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Multiple Choice

What do CPA and TCPA stand for, and how are they used?

The main idea being tested is how moving objects are analyzed for collision risk using their relative motion. CPA and TCPA come from comparing two vessels’ speeds and courses to predict what would happen if they continue on those paths. CPA stands for Closest Point of Approach—the closest distance two vessels would reach if they keep their current speeds and directions. TCPA stands for Time to Closest Point of Approach—the time at which that closest distance would occur. These metrics let you judge risk and timing: a small CPA means the vessels would pass very close, and a small TCPA means that moment is near, signaling a potential collision unless action is taken. Negative TCPA indicates the closest approach would have happened in the past if the current motions continue. In practice, you use CPA and TCPA on radar/ARPA displays or in calculations to decide whether to alter course or speed to increase the distance at closest approach or the time until that moment, based on safe thresholds for the specific vessels involved. Choices that are not about how two moving objects relate in space and time aren’t describing these terms. They aren’t current position or target course, they aren’t weather terms, and they aren’t measures of radar resolution.

The main idea being tested is how moving objects are analyzed for collision risk using their relative motion. CPA and TCPA come from comparing two vessels’ speeds and courses to predict what would happen if they continue on those paths.

CPA stands for Closest Point of Approach—the closest distance two vessels would reach if they keep their current speeds and directions. TCPA stands for Time to Closest Point of Approach—the time at which that closest distance would occur. These metrics let you judge risk and timing: a small CPA means the vessels would pass very close, and a small TCPA means that moment is near, signaling a potential collision unless action is taken. Negative TCPA indicates the closest approach would have happened in the past if the current motions continue. In practice, you use CPA and TCPA on radar/ARPA displays or in calculations to decide whether to alter course or speed to increase the distance at closest approach or the time until that moment, based on safe thresholds for the specific vessels involved.

Choices that are not about how two moving objects relate in space and time aren’t describing these terms. They aren’t current position or target course, they aren’t weather terms, and they aren’t measures of radar resolution.

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