Within what time frame should ARPA present an object's predicted motion?

• A. Within 1 minute
• B. Within 3 minutes
• C. Within 5 minutes
• D. Within 15 minutes

Answer: (B)

ARPA’s predicted motion is a short-range forecast of where a tracked object will be in the near future, based on its current course and speed. The idea is to give the navigator enough time to assess risk and decide on an action, while keeping the forecast reliable.

Three minutes is the practical horizon because it provides a useful planning window for collision avoidance without relying on more uncertain long-term behavior. Predictions beyond this interval become less reliable due to potential course changes, speed variations, or maneuvers by the target, so the ARPA forecast stays accurate enough to inform decisions within that time frame. Shorter horizons, like one minute, may not give sufficient time to react in fast-developing situations, while longer horizons (five or more minutes) tend to overestimate certainty and risk.