Originally Posted by
jahason
A despatcher once told me flight routes are also designed so that they are never more than an hour's flying time from an airport, as much as possible. So flights across South Atlantic fly close enough to the Azores. Not sure if I remember details absolutely correctly.
That's true for most two engined aircraft which are not rated for extended operations (ETOPS). You need to be within 1 hour diversion flying time on one engine to an airport. Obviously for flights across Europe is isn't an issue. However, I would imagine most aircraft used regularly for trans ocean flights would have a more relaxed requirement. A number of aircraft can be approved for ETOPS ratings where the flying time can be a lot more than 1 hours. Typically I think ETOPS 180 is common - so you can route such that you are within 180 minutes one engine flying time of a diversion airport at all times. Higher ETOPS ratings are possible to I believe.
ETOPS 180 aircraft can be wide bodies such as 777/A330, and narrow body aircraft can also be rated higher. AA uses specific ETOPS rated A321 aircraft from LAX/PHX to Hawaii for example, and BA's babybus would be ETOPS rated.
Probably better explained here
https://en.wikipedia.org/wiki/ETOPS the diagram makes it a bit easier to understand.