Comment by sitharus

Comment by sitharus 3 days ago

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.

dylan604 2 days ago

> 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.

Do they also decrease the opposite engine to help with this as well?

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dredmorbius 2 days ago

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...>
<https://en.wikipedia.org/wiki/Al_Haynes>

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