TCPA (Time to Closest Point of Approach)

Time to Closest Point of Approach is the time to CPA if both vessels maintain course + speed. Combined with CPA, TCPA tells the OOW when the collision-risk window is — a target with CPA 0.3 NM + TCPA 20 min needs early action; CPA 0.3 NM + TCPA 3 min is imminent. ARPA + ECDIS displays; alarms typically set at TCPA 12 min in open water.