What is ARPA and what is its primary function?

• A. Automatic Radar Plotting Aid; automatically tracks targets, computes CPA/TCPA, and displays predicted tracks and alerts.
• B. Manual radar plotting tool.
• C. A device for measuring wind speed.
• D. A satellite navigation system.

Answer: (A)

ARPA stands for Automatic Radar Plotting Aid. Its primary function is to automatically track detected targets, calculate collision avoidance metrics such as the closest point of approach (CPA) and the time to CPA (TCPA), and display predicted tracks with alerts when a potential collision exists. This automation helps the crew maintain situational awareness and make timely decisions, especially in busy traffic or poor visibility. The other options describe tools that do not perform automatic target tracking and CPA/TCPA calculations: a manual radar plotting tool requires manual plotting; a device for measuring wind speed is unrelated; and a satellite navigation system provides positioning rather than automated radar-based tracking and alerts.