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[LC0112G]

Only way a birdstrike makes sense is if the engine swallowed a big bird (or birds) and suffered enough damage for the resulting vibrations to shake the engine off the wing. Not impossible, but not very likely either.

The engine pylon fixings are frangible - they are supposed to break if there is enough engine vibration to endanger the structural integtiry of the wing/airframe. AIUI the MD-11 has two main engine fixings on each pylon under the wing. There was a previous crash where the rear fixing broke, but that caused the engine to pivot forwards and upwards, and it departed over the top of the wing. That doesn't appear to have happened here. My money is on the front fixing breaking, which I think would result in a forwards and downwards departure if it happened at or after rotate when the wing is pulling upwards.

If that's correct, then we're looking at either poor maintainace, or counterfeit parts. It's also possible there was a fire in the wing first, which then damaged the fixings. Either way, nothing the crew could do, and once the second tail engine starts to lose thrust the outcome is sealed. No way a heavy MD-11 is going anywhere but down on one engine.

RIP the crew, and those caught on the ground.

[Viral_Jim]

This has happened before on a DC10

Do you mean This one?

If so you'd hope that the lesson of not fuŁking about with the manufacturer's maintenance procedures had been well learned! 

[Doctor Gollum]

It would take quite a bird strike to rip an engine off its pylon and dump it by the runway, but it's not impossible that one started the whole chain of events, I suppose.

By the time it's bounced over the airfield, the external gubbins would have been smashed to bits, the core is the heaviest part so no surprise that it's on its own.

The pylons have always been a week link on those. DC10/MD11s. The AD that came from the Chicago crash in the late seventies focused on maintenance practices rather than the aircraft. The engines themselves aren't actually held on by much.

Whilst the casing should be able to contain a fan blade failure, regardless if cause, the rotational force at take off power could have been enough to twist the pylon off.

Engine #2 probably ingested the fragments of #1 as it disintegrated., something more likely due to the relative tail position as the nose came up. By contrast, the engine in the Chicago incident simply became detached and missed the tail. In this case the engine coming away was a secondary event. As was the engine fire. Once the engine came away, the subsequent roll to the left was guaranteed.
#2 failing was actually a blessing as the aircraft never gained altitude.

FOD or mechanical failure.

[Doctor Gollum]

This has happened before on a DC10

Do you mean This one?

If so you'd hope that the lesson of not fuŁking about with the manufacturer's maintenance procedures had been well learned! 

The only similarities are aerodynamic consequence. Erase that engine and it's thrust and the resultant roll is swift and catastrophic and will happen every single time.

Incidentally, not many operators own any and fleet utilisation is pretty low...

https://en.wikipedia.org/wiki/List_of_McDonnell_Douglas_MD-11_operators

[Kevin Wood]

This has happened before on a DC10

Do you mean This one?

If so you'd hope that the lesson of not fuŁking about with the manufacturer's maintenance procedures had been well learned! 

The only similarities are aerodynamic consequence. Erase that engine and it's thrust and the resultant roll is swift and catastrophic and will happen every single time.

Incidentally, not many operators own any and fleet utilisation is pretty low...

https://en.wikipedia.org/wiki/List_of_McDonnell_Douglas_MD-11_operators

The main issue with AA191's loss of control was retraction of the slats on the port wing and the consequent asymmetric stall due to hydraulic damage, an issue that was countered by an AD in response to the crash investigation.

There's no roll I can see on the videos of this crash, at least not until the port wing contacts something solid on the ground and the airframe cartwheels.

Aerodynamically, it's an engine failure, so possible to counter with control inputs assuming you still have a working system by which to make them.

Add a load of fire and a second engine failure and there is, of course, no hope.

[Doctor Gollum]

AA191 had alot more altitude so was almost inverted when it hit.

The two things they needed they didn't have... Airspeed and altitude. The wings will always provide lift as long as there is air flowing over it. Removing thrust on one side causes a loss of airspeed over that wing. Less airspeed equals less lift. Likewise the yaw induced by the loss of balanced thrust further slows the unpowered wing causing more loss of lift. As the wing drops the aircraft will always roll to that side. Once the left wing touched the lift from the working wing finished the roll.

Not dissimilar to the Endeavour crash in Toronto earlier this year.

The position of the tail engine relative to the dynamic axis is less than ideal compared to the Tristar or other three engined aircraft. Where the centre line of the engine is almost aligned with the centre line of the aircraft.

[Kevin Wood]

The two things they needed they didn't have... Airspeed and altitude. The wings will always provide lift as long as there is air flowing over it. Removing thrust on one side causes a loss of airspeed over that wing. Less airspeed equals less lift. Likewise the yaw induced by the loss of balanced thrust further slows the unpowered wing causing more loss of lift. As the wing drops the aircraft will always roll to that side. Once the left wing touched the lift from the working wing finished the roll.

Yes, but all of these effects of asymmetric thrust are possible to counter with control inputs until the wing stalls, which didn't happen in this incident, judging by the footage I've seen, but did, almost instantly, for AA191 due to slat retraction below the clean stalling speed. I'd say the crew in this case did a great job of keeping the aircraft flying to the crash site. Sadly, it didn't help them or the souls on the ground.

[LC0112G]

It is not true that "wings will always provide lift as long as there is air flowing over it". Once a wing stalls, all it provides is drag.

AA191 crashed in the way it did because the crew reduced speed to V2 when they realised something was wrong. That's what the checklist says to do on a DC10 in the event of engine failure during take-off/climb out. However, the crew did not realise they had also lost hydraulic pressure in the left wing, and that loss caused the leading edge slats to retract. With no leading edge slats, V2 is not fast enough for a wing to produce lift and the left wing stalled. The right wing did still have flaps an slats, so was still producing lift. The result of lift on the right wing and a stall on the left wing are what caused AA191 to roll left and crash in the way it did. If the crew had maintained their original speed, the left wing would not have stalled, it would not have rolled left, and simulator test showed the plane could have remained airborne - although given it was on fire and had compromised hydraulics no way of knowing how long it could have remained airborne.

In this case, the plane appears to have been level until it hit the ground. Dashcams show no evidence of roll.

[Doctor Gollum]

I may have worded that better: in a normal attitude with sufficient air moving at a high enough speed would have been clearer.

All slats and spoilers do is change the shape of the wing as required to maximise lift/reduce drag at any given airspeed. Note that drag is not the opposite of lift.

It's a pretty moot point though... 150ft isn't enough altitude to do anything with.