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Comment by londons_explore | Hacker News Reader

I was under the impression that a plane could deal with an engine failure at any point in flight - including during takeoff.

Dropping an engine entirely is a similar situation to a failure - with the benefit that you now have a substantially lighter if imbalanced aircraft.

Should this plane have been able to fly by design even with an engine fallen off?

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El Al 1862 was another flight [1] that had an engine fall off, taking another engine out with it. The pilots managed to fly around for a few minutes and attempt a landing, but there was too much structural damage.

It doesn't seem aircraft are designed to survive these types of catastrophic failures.

[1] - https://en.wikipedia.org/wiki/El_Al_Flight_1862

They seem to have lost the tail engine too. Yes, it is a significant problem that engine failures aren't independent, so trijets are kind of a bad design.

Not only did it happen at the worst possible moment, it took out a second engine on it's way out and over the plane. Two engines should've been enough to get off the ground and potentially land the plane, but one engine on a trijet isn't enough.

Yes, but when the engine came off, it also disrupted the third engine in the tail. Can't take off in this model with 2 out of 3 engines gone.

Even if they had the thrust (doubtful) there wouldn't be enough lift with a gaping hole in the leading edge of one wing.

Yeah, if they had had more altitude, I would guess that this would have looked even more like the AA 191 crash from 1979, with the left wing stalling and causing a roll and pitch down.

That in turn reminds me of the DHL flight out of Baghdad in 2003 that was hit by a missile [0]. Absolutely amazing that they managed to keep it together and land with damage like that.

[0] https://en.wikipedia.org/wiki/2003_Baghdad_DHL_attempted_sho...

An important factor in AA 191 is that the engine leaving did significant damage to the hydraulic lines in that wing - including those for the leading-edge slats. At the time the plane was not equipped with any mechanism to keep the slats extended, so after hydraulic pressure was lost airflow over the wings caused them to retract, which significantly lowered that wing's stall speed.

After AA 191 the DC-10 was equipped with a locking system: loss of pressure now results in the slats getting stuck in their current position. The MD-11 will undoubtedly also have this system, so a direct repeat of AA 191 is unlikely.

> significantly raised the stall speed

(yeah, it's one of those weird metrics where "bigger is worse", so you're absolved)

The video of the aircraft crossing the road wings level (well after #1 separated) and maintaining relatively controlled flight until too much energy bled off suggests to me the aircraft was likely to be controllable to a landing if sufficient thrust was available.

..for a moment. If there was sufficient hydraulics damage it might've stopped being controllable.

And even if they worked the fire might've damaged the plane enough.

For example https://www.faa.gov/lessons_learned/transport_airplane/accid...

when they lost tail engine, all of the hydraulics went down

To be clear, we don't yet know if the UPS flight lost hydraulics or not. There are several somewhat redundant hydraulic systems.

(Also, as a result of the Sioux City crash you linked, there were several ADs issued requiring changes to hydraulics in these airframes.)

I thought the leading edge of the wing was intact in this case? I may be misremembering.

Yeah, pilots I know saw puffs of flame coming out of the engine, and said that that's a tell-tale sign of a compressor stall. Which could have been caused by debris from the separating left engine striking the turbine.

Debris, or even just smoke from the wing fire.

It was specifically the distinct, rhythmic puffing. I'm not sure you could expect the same pattern from debris or a wing fire.

I think they were saying that smoke/particulates could be sufficient to upset the rear engine-- things short of what we ordinarily call "debris".

I'm just saying that smoke alone can cause a compressor stall -- it doesn't necessarily require larger debris.

Ah, gotcha. My bad.

It didn’t fall off, it flew up and then landed back on the plane.

https://www.reddit.com/r/aviation/comments/1p276xx/ntsb_issu...

And also ripped open a giant hole in the fuel tank which allowed all of the fuel to be released and ignited.

It nuked the tail engine so actually TWO engines failed.

From the wing down I assumed it may have depended if the engine coming out unintentionally means redundant hydraulic lines and mounts are also getting disconnected causing a complete loss of control not that it would have helped much at that point beyond minimizing ground damages.

This engine didn’t just fail, it failed catastrophically and took out another engine with it.

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