Definition
The portion of a twin-engine airliner's flight route that lies beyond 60 minutes' flying time (at single-engine cruise speed in still air) from the nearest suitable diversion airport. Operating in this segment requires the aircraft, the operator, and the route to be specifically approved under ETOPS rules.
Plain English
It is the part of a flight where a two-engine airliner is far enough from any landing airport that special rules apply in case one engine fails. Both the airline and the airplane have to be specially approved to fly that part of the route.
Context Anchor
Seen in airline flight planning, dispatch releases, long overwater routes, remote-area routes, and ETOPS alternate-airport planning.
Derivation
ETOPS originally stood for Extended-range Twin-engine Operational Performance Standards. The word 'segment' here just means a defined portion of the route — the part where these extended-range rules apply.
Why Pilots Care
It determines required fuel loads, engine maintenance standards, and crew training so the aircraft can reach a diversion airport safely if an engine fails.
Intuition Check
Do not treat an ETOPS segment as just any section of a route. It is specifically the section between the ETOPS entry and exit points where ETOPS rules are active.
Example Sentence 1
Before crossing the Atlantic, the crew briefed the diversion airports for each ETOPS segment of the flight.
Example Sentence 2
Once inside the ETOPS segment the crew confirmed both engines were operating normally and all diversion airports remained available.