By staying as close to land as required to ensure safety. until fairly recently, flights to Hawaii were largely served by 3- or 4-engine jets. It's only in the last several decades that ETOPS regulations have shifted enough to allow regular twin-engine service to Honolulu.

See the 3rd response... https://www.airliners.net/forum/viewtopic.php?t=119921

The regulations have been shifted but only time will tell if it should be shifted. I guess we'll find out in 20 years.

Thanks for the recommendation on that 3rd response, it was an excellent reply

The "certain number of minutes" includes being over oceans. If you're too many minutes, you can't fly there. ("Minutes" are fairly large. I believe at least one Airbus aircraft is now at 4 hours.)

Transoceanic aircraft need lots of ETOPS time. For example the boeing 777 (twin-engine, transoceanic) has an ETOPS of 330 minutes, so it always needs to be 330 min away from an airport (which is 11 hours of flight from airport A to airport B, not taking wind into account)

By having airports on islands, or by pushing up the number of minutes that the engines/operator are certified for.

Note that ETOPS goes beyond just engine ratings, it also requires the operator meet all sorts of additional requirements (what if you DO have to divert - can you have the passengers retrieved within 24 hours, do you have food and shelter if you have to divert to a non-commercial airport along the flight path, are your technicians doing proper maintenance, etc).

Good point. Edited my comment to add that :)

For transatlantic flights, two important "backups" are in Iceland and in the Azores. I wonder how often airplanes actually have to detour to these airports...

Happens fairly regularly but for passenger issues rather than technical- medical emergencies and disruptive passengers usually.

Airlines have contracts with companies who provide a sat phone link to doctors who have the flight information and medical facilities at possible diversion airfields. Eg MedAire.

It happens: I was on an London - USA flight that detoured to Iceland some years ago. (Fortunately nothing was seriously broken, burning, etc., but there was a warning indication of some kind that the pilot wanted to have checked.)

The view coming in to Keflavik, with whales swimming in the ocean below, was pretty cool.

Years ago I was on a 747 from SFO to LHR that landed in Iceland - oil pressure problem in an engine. A guy drove out with a pickup truck, climbed into the engine using a ladder in the back of the truck, and started hammering away. After a few hours in the terminal we got back on the plane and flew the rest of the way to LHR. I kept wondering just how qualified he was...

Last I know of is https://en.wikipedia.org/wiki/Air_Transat_Flight_236 running out of fuel.

You stay close to land as much as possible. For example, LA to Tokyo, you basically fly up the west coast, give Canada's west coast a high five, and then come around below Alaska. It's less direct than it could be, but it's much safer in the event of an emergency.

It is more.direct than it sounds though because the earth is round and so the shortest distance between two points curves.

ETOPS accounts for oceans. Please read the link.

Very few in service aircraft in commercial passenger fleets have more than two engines, and even the ones with more than two engines have modified ETOPS rules to comply with.

The two that come to mind are the 747 and a380

Generally transatlantic jetliners have more than 2 engines, although I suppose that’s beginning to change.

The vast majority of transatlantic airliners today are two engine aircraft. For four engines, you’re basically looking at 747s and maybe the odd a340 that has somehow escaped retirement. The last large four engine airliner will go out of production next year.

That really hasn't been true since 747s started to be retired so it started to change years ago and 2-engine is now essentially the norm.

This has not been true for a decade