Luckily flight plans are always required to be within a certain number of minutes of a place to land, and are certified to operate on one engine for that period.
Indeed. The scary part here isn’t the loss of (function in) one engine, it’s structural issues, fire and so on. A violent engine failure can give a whole range of problems beyond just the loss of the engine. It would likely have been ok even half way to Hawaii, but it would have been scary.
ETOPS helps but it assumes that the engine is just shut down. Here you have compromised aerodynamics and potentially the wing, tail or other systems damaged by the parts of engine
Of course. But simply an engine not working shouldn't be a concern. Obviously land as soon as possible, but it's not really that dangerous (assuming the other engine doesn't fail for the same reason)
Turbine blades failing and piecing a hydraulic line on the other hand...
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.
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)
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).
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...
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.
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 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.
