Radar Observer · Plotting — TCPA
A target's range is 6.0 NM and it is closing at a steady 12 knots on a constant bearing. The time to the closest point of approach (TCPA) is:
- A12 minutes
- B60 minutes
- C30 minutes✓ Correct
- D72 minutes
Explanation
On a constant (steady) bearing the CPA is zero — a collision course — so the TCPA is simply range ÷ closing rate = 6.0 NM ÷ 12 kt = 0.5 h = 30 minutes. A constant bearing with decreasing range is the classic radar collision indicator.
Authority: Bowditch (Pub. No. 9), Radar Plotting
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