FAA Airline Transport Pilot (ATM)Navigation, Air Traffic Control and ProceduresHard
A twin-engine airliner is dispatched on an ETOPS 180-minute route over water. The approved one-engine-inoperative diversion cruise speed is 320 knots. What is the maximum distance the flight's route may take it from an adequate enroute alternate airport?
- A480 NM
- B960 NM
- C640 NM
- D1,200 NM
Show answer & explanationAnswer & explanation
Correct answer: B. 960 NM
ETOPS 180 authorizes a diversion time of 180 minutes (3 hours) at the one-engine-inoperative cruise speed. Distance = speed × time = 320 kt × 3 hr = 960 NM. This is the maximum distance the route can be from a qualifying alternate.
Why the other options are wrong
- A. This would correspond to only a 90-minute diversion, not 180.
- C. This corresponds to a 120-minute diversion time, not the ETOPS-180 authorization.
- D. This exceeds the 180-minute authorization; it corresponds to roughly 225 minutes.
ETOPS Diversion Distance
ETOPS (Extended Operations) authorizations specify a maximum diversion time from an adequate alternate; multiplying that time by the one-engine-inoperative cruise speed gives the maximum allowable route distance from an alternate.
- Common ETOPS ratings: 120, 138, 180, and beyond
- Distance = OEI cruise speed × diversion time
- Route planning must keep the aircraft within this distance of a suitable airport
- Higher ETOPS ratings require additional reliability and maintenance approval
Memory trick: 'ETOPS math: Speed times Time equals how far you can fly from safety'