4 ms·

Not exactly a single point of failure. It's obviously not good if one fails and the engine falls off the plane, but, a 777X should still be able to fly with a

Not exactly a single point of failure. It's obviously not good if one fails and the engine falls off the plane, but, a 777X should still be able to fly with a single engine. Of course, that capability is more geared to "we saw a high temperature on the engine so let's proactively shut it down and land as soon as we can" and not "the engine fell off the plane and landed on someone".

SoftTalker 2y ago
And if one falls off due to a structural weakness, the other might well soon follow.
giosalinas 2y ago
obviously not good if one falls off the plane????!! you are talking about major structural damage to the airplane, the center of mass will be completely off and the airplane will fall as hard as a rock.
- wkat4242 2y ago
  If one falls off the way it was planned it will be a very bad but not necessarily terrible situation. Someone else already linked to the excellent admiral cloudberg article that describes how it should have happened (which there it didn't), as designed the engine would flip over the wing and not hit anything. Though of course the damage to the wing and pylon might rip hydraulics or wiring out or something. It's never a good thing. Also, the engines are pretty close to the centre of mass so it's not a huge deal. Asymmetric thrust will be a problem but the drag situation will be better than with 1 engine disabled! After all there is no inactive engine face catching a whole load of air. And an engine failure situation is already a known situation.
  - giosalinas 2y ago
    Well, El Al 1862 crashed anyways, isn't it? You can't compare losing 1/4 engines to 1/2 of the massive GE9X engines and center of mass will be off by a lot. There are several crashes related to weight imbalance (usually cargo bay) and there is a reason why there are several precautions regarding how to load a plane. We also have the 737-Max, that needs a counterbalance mechanism to make it work.
    - wkat4242 2y ago
      Yes but it crashed because the pylons failed in the wrong way. It was a design flaw. Also, if it had failed as designed it would have only lost one. The other one was only lost because the first engine hit it on the way out. As well as the leading edge of the wing and the slats. The plane was doomed but not because of imbalance. It just could not fly under 270 knots.
- jojobas 2y ago
  Structural damage aside, modern planes have ridiculous safety margins on center of mass, drag and lift. A cleanly separating engine wouldn't be that much of a problem, mostly sorted by pumping fuel and rudder trim.
epc 2y ago
You wouldn't think a single engine could be a single point of failure but the crash of AA 191 in 1979 was due to a cracked engine mount.
pixl97 2y ago
There was a 747 crash in (poland or the netherlands) where the bolts broke off the engine and the failed engine managed to hit the other engine on the wing. The plane fell straight out of the sky and cut an apartment building in two killing at least 40 on the ground. Engines falling off a plane are very very bad and cause a lot of secondary damage.
- alvah 2y ago
  https://en.wikipedia.org/wiki/El_Al_Flight_1862 https://en.wikipedia.org/wiki/El_Al_Flight_1862
FabHK 2y ago
A DC-10 can't fly when one engine comes off unplanned (and it has two engines left in that case...): as the aircraft was beginning its takeoff rotation, engine number one (the left engine) separated from the left wing, flipping over the top of the wing and landing on the runway. As the engine separated from the aircraft, it severed hydraulic lines that lock the wing's leading-edge slats in place and damaged a 3-foot (1 m) section of the left wing's leading edge. Aerodynamic forces acting on the wing resulted in an uncommanded retraction of the outboard slats. As the aircraft began to climb, the damaged left wing produced far less lift than the right wing, which had its slats still deployed and its engine providing full takeoff thrust. The disrupted and unbalanced aerodynamics of the aircraft caused it to roll abruptly to the left until it was partially inverted, reaching a bank angle of 112°, before crashing in an open field by a trailer park near the end of the runway. The engine separation was attributed to damage to the pylon structure holding the engine to the wing, caused by improper maintenance procedures at American Airlines. https://en.wikipedia.org/wiki/American_Airlines_Flight_191 https://en.wikipedia.org/wiki/American_Airlines_Flight_191
fransje26 2y ago
> Not exactly a single point of failure. It is a safe-life part, so yes, it is a single point of failure part for that engine. And, if something fails unexpectedly, it could significantly damage the wing too, as has happened in the past with deadly consequences. The problem being encountered on two other test planes, makes it a lot more problematic, as the probability of the second engine shearing off then becomes a lot, lot higher.

SoftTalker 2y ago

And if one falls off due to a structural weakness, the other might well soon follow.

giosalinas 2y ago

obviously not good if one falls off the plane????!! you are talking about major structural damage to the airplane, the center of mass will be completely off and the airplane will fall as hard as a rock.

wkat4242 2y ago
If one falls off the way it was planned it will be a very bad but not necessarily terrible situation. Someone else already linked to the excellent admiral cloudberg article that describes how it should have happened (which there it didn't), as designed the engine would flip over the wing and not hit anything. Though of course the damage to the wing and pylon might rip hydraulics or wiring out or something. It's never a good thing. Also, the engines are pretty close to the centre of mass so it's not a huge deal. Asymmetric thrust will be a problem but the drag situation will be better than with 1 engine disabled! After all there is no inactive engine face catching a whole load of air. And an engine failure situation is already a known situation.
- giosalinas 2y ago
  Well, El Al 1862 crashed anyways, isn't it? You can't compare losing 1/4 engines to 1/2 of the massive GE9X engines and center of mass will be off by a lot. There are several crashes related to weight imbalance (usually cargo bay) and there is a reason why there are several precautions regarding how to load a plane. We also have the 737-Max, that needs a counterbalance mechanism to make it work.
  - wkat4242 2y ago
    Yes but it crashed because the pylons failed in the wrong way. It was a design flaw. Also, if it had failed as designed it would have only lost one. The other one was only lost because the first engine hit it on the way out. As well as the leading edge of the wing and the slats. The plane was doomed but not because of imbalance. It just could not fly under 270 knots.
jojobas 2y ago
Structural damage aside, modern planes have ridiculous safety margins on center of mass, drag and lift. A cleanly separating engine wouldn't be that much of a problem, mostly sorted by pumping fuel and rudder trim.

epc 2y ago

You wouldn't think a single engine could be a single point of failure but the crash of AA 191 in 1979 was due to a cracked engine mount.

pixl97 2y ago

There was a 747 crash in (poland or the netherlands) where the bolts broke off the engine and the failed engine managed to hit the other engine on the wing. The plane fell straight out of the sky and cut an apartment building in two killing at least 40 on the ground. Engines falling off a plane are very very bad and cause a lot of secondary damage.

alvah 2y ago
https://en.wikipedia.org/wiki/El_Al_Flight_1862 https://en.wikipedia.org/wiki/El_Al_Flight_1862

FabHK 2y ago

A DC-10 can't fly when one engine comes off unplanned (and it has two engines left in that case...): as the aircraft was beginning its takeoff rotation, engine number one (the left engine) separated from the left wing, flipping over the top of the wing and landing on the runway. As the engine separated from the aircraft, it severed hydraulic lines that lock the wing's leading-edge slats in place and damaged a 3-foot (1 m) section of the left wing's leading edge. Aerodynamic forces acting on the wing resulted in an uncommanded retraction of the outboard slats. As the aircraft began to climb, the damaged left wing produced far less lift than the right wing, which had its slats still deployed and its engine providing full takeoff thrust. The disrupted and unbalanced aerodynamics of the aircraft caused it to roll abruptly to the left until it was partially inverted, reaching a bank angle of 112°, before crashing in an open field by a trailer park near the end of the runway. The engine separation was attributed to damage to the pylon structure holding the engine to the wing, caused by improper maintenance procedures at American Airlines. https://en.wikipedia.org/wiki/American_Airlines_Flight_191 https://en.wikipedia.org/wiki/American_Airlines_Flight_191

fransje26 2y ago

> Not exactly a single point of failure. It is a safe-life part, so yes, it is a single point of failure part for that engine. And, if something fails unexpectedly, it could significantly damage the wing too, as has happened in the past with deadly consequences. The problem being encountered on two other test planes, makes it a lot more problematic, as the probability of the second engine shearing off then becomes a lot, lot higher.