Comment by bangaladore 3 days ago
Incase anyone is wondering about ETOPS-N
For example, if an aircraft is rated for ETOPS-180, it means that it is able to fly with full load and just one engine for three hours. [1]
Obviously in this case it 5hours 30 minutes on one engine at full load.
-- Slight edit: Unclear if with a 4 engine its rated with 2 functional or still 1 functional engine.
Flying multi-engine aircraft with an engine shut down is a routine training and test maneuver, so these aircraft have all been flown a lot of hours with an engine out. The tricky thing about ETOPS is ensuring very high engine reliability (so that the probability of coincidentally having two engines fail on a flight is low) and avoiding failure modes that would affect both engines at once (one of the reasons for a lot of redundancy in electrical systems).
And while technically different rules, ETOPS in practice gets attached to other requirements for transoceanic flights, so ETOPS aircraft often have additional life rafts and other equipment.
There’s a bunch of regulations, but from looking through them quickly I think they start with a bunch of testing and analysis initially to show a predicted rate under the requirement, and afterwards they look at the real-world rate with a 12-month rolling average.
Apparently the acronym can now be read as the blander "ExTended OPerationS", or according to the ICAO all such flights can be referred to as EDTO (Extended Diversion Time Operations", which is less fun to say out loud and loses the joke definition "Engines Turn Or People Swim")
I'm not sure. In the case of 4 engines, it may be 2 is how they certify it. Specifically I think the case where both engines on the same wing fail (as the worst case other that losing 3)
Yes they’ll use more fuel than running on all engines. They always load the extra fuel that would be required for the maximum flight time with an engine out.
The extra fuel burn is due to the drag from pushing a non-working engine through the air, and from the rudder deflection to counteract the unequal thrust. It’s less of an issue on a four engine aircraft with a single engine out as they can increase thrust on the remaining engine on the side with the engine out.
Extra fuel burn is also required because a twin engine aircraft with an engine out can’t maintain the normal cruising altitude, and the higher you are the more efficient the engines are.
Thrust can’t be reduced much to save fuel because the speed margins at altitude are quite narrow - if they reduce thrust and therefore airspeed they’ll descend.
That's an option.
Aircraft with disabled flight controls have occasionally steered / maneuvered utilising variable engine thrust alone. A notable instance is UA 232 (1989), Denver Stapleton to Chicago O'Hare, which crashed on landing at Sioux City, Iowa. Despite a nearly completely disabled aircraft and a violent landing, there were 184 survivors of 296 souls, including the pilot Alfred Clair Haynes (he died in 2019, aged 87).
The aircraft, a DC-10, suffered an uncontained fan failure which severed all three hydraulic control systems, disabling virtually all flight control surfaces (elevators, ailerons, rudder), and the pilots (with assistance from a dead-heading pilot/instructor passenger) controlled both horizontal and vertical orientation using engine thrust alone.
I've heard and read numerous times that in simulations of the incident afterwards few or no pilots managed to land the plane. Haynes was an absolute master pilot.
<https://en.wikipedia.org/wiki/United_Airlines_Flight_232#Att...>
I believe it's not just that it is able to fly with 1 engine. It's that the probability of a secondary engine failure in that time is below a certain threshold. Most twin engine planes can fly perfectly fine for basically any distance with an engine out, ETOPs provides confidence that the other one won't fail too.