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Boeing 787 Suffers Rare Dual Engine Failure on Landing

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Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#331

Post by tlb »

vpribish wrote: post #284
tlb wrote: post #248

Earlier quoted context omitted.

Feynman says yes, except at very low speeds. https://en.wikipedia.org/wiki/Feynman_sprinkler

that's very interesting! but it's about angular momentum and I'm not confident that I can take the lesson over to linear momentum. Here's my caveman f=ma thought experiment: 1. make it 2-d. 2. replace the fan with a person sitting on a chair on a frictionless surface. 3. instead of air it's an endless field cinder blocks ahead of him. the person reaches out, and pulls in a cinder block. f=ma says they each move towar…

You have to look for the equal and opposite reaction. A normal jet creates a stream of fast air behind it. There's no such thing for a reverse jet that sucks air in.

With your concrete block example, as I start pulling the block towards me I experience an impulse forward. But when it approaches my body I slow it down to zero speed, creating an opposite impulse. So although I might have moved forward a few inches during the motion, my momentum is zero at the end. When you scale this up to large numbers of air molecules, the result is the same.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#332

Post by grkvlt »

sandworm101 wrote: post #310
esemor wrote: post #189

I think the auto shutdown of engines in flight, in case it senses reverse thrust, is a great design. The 787 is a replacement for my 767 (currently a pilot on the aircraft) and in 1991 a Lauda Air 767 suffered a failure in one of its thrust reverser and it became activated during cruise. The aircraft was destroyed in flight. The thrust reversers should not activate during flight (a air/ground sensors prevents that) b…

Fyi, military pilot here, there are a handful of mil aircraft that can reverse thrust in flight. A great too for dropping down fast to avoid low/slow flight over hostile areas. There might be a relationship between that ability and this problem.

Also, as I recall, Concorde could do this too...

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#333

Post by ars »

isostatic wrote: post #234
frogpelt wrote: post #219

Earlier quoted context omitted.

A better comparison might be putting the car in reverse at 60 MPH.

You never missed a gear, thinking you were driving a 6 speed rather than a 5 speed?

The sleeve of my coat caught on the gear shift while making a left turn and threw it in reverse while on the freeway.

It made a grinding noise and I yanked it back into drive.

Other than the noise nothing bad happened.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#334

Post by exabrial »

phkahler wrote: post #135
exabrial wrote: post #12

Sort of off topic, but reverse thrust sort of boggles my mind. If you're sucking air in from the front of the aircraft and ejecting it out the front, don't those forces counterbalance each other?

If the suck force and the blow force were equal, you wouldn't need to burn fuel inside the engine during normal operation. Combustion produces a lot higher volume of gasses at higher energy than the air that goes in the front.

I initially thought this as well, but it turns out that the reverse thrust is actually made of bypass air in most engines

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#335

Post by repiret »

soheil wrote: post #328
tjohns wrote: post #309

Earlier quoted context omitted.

My advice is to look at the statistics. Commercial flying is much, much safer than any other mode of transport. Do you get scared when you drive to work? Or take a train? Both are more risky. (Driving significantly so.) More specifically... The pilots have extensive training, modern airliners have fail safes everywhere, and the amount of research and engineering spent on aviation safety is mind boggling. See: http://…

An accident during flight is pretty much a binary event when it comes down to whether you live or not, but with cars there is a whole slew of different types of accidents and vast majority of them don't cause instant death preceded by 45 seconds of absolute terror. Before you downvote what I said in no way discounts the statistics. It is much safer to fly of course than to drive, but when we think of accidents which…

I agree with what you say, but I think it has more to do with (perceptions of) control than the failure modes.

When you’re in an automobile, you could choose to drive faster or slower, safer or more aggressively. You can tell yourself that you are more alert or a better driver to the people who die in fatal car accidents. You can tell yourself that you have a superior ability to avoid that drunk driver who might suddenly veer into your lane from oncoming traffic. And once your car comes to a stop, if you’re not seriously injured, you can just get up and walk away.

In an airplane there’s none of that. You can make vanishingly few choices to affect the safety of your flight. And you’re stuck in that tin can until it’s on the ground and you’re either alive or dead.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#336

Post by jstanley »

camtarn wrote: post #295
stevehawk wrote: post #278

Earlier quoted context omitted.

No, but for as long as I've been driving manual cars they've had gates to prevent that very action. (1995)

Not mine (Honda Jazz). But you physically can't do it, as the reverse gear has no synchro and won't mesh unless stationary.

It can be done, but it's neither easy nor a good idea: https://youtube.com/watch?v=ARJENV0qGdY

You'd certainly struggle to do it by accident.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#337

Post by fulafel »

heyjudy wrote: post #302
outworlder wrote: post #254

Earlier quoted context omitted.

> it's a great fail safe but not if you lose your engines in flight and can't relight them like in the article. It is still better to lose all engines than to have thruster reversers deploy in unsafe situations. You may stall without an engine at low altitude in a landing configuration, but you should still be able to glide for some time. Deploy reversers (or even a single reverser) and you fall like a brick very qui…

This existing system wouldn't likely cause loss of all engines unless the PIC commanded all engines TR in-flight. Also, it doesn't make sense that such a system would go out untested because such a system should try command engines to idle before cutting fuel to what it thinks are runaway engines. Finally, it's still unknown if it's a Boeing software issue or a RR T1K issue... the OP article is purely speculative and…

A single engine on reverse is enough to mess up the the flight violently enough that it'll break apart before hitting the ground (see the Lauda Air case).

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#338

Post by esemor »

zepearl wrote: post #304
esemor wrote: post #189

I think the auto shutdown of engines in flight, in case it senses reverse thrust, is a great design. The 787 is a replacement for my 767 (currently a pilot on the aircraft) and in 1991 a Lauda Air 767 suffered a failure in one of its thrust reverser and it became activated during cruise. The aircraft was destroyed in flight. The thrust reversers should not activate during flight (a air/ground sensors prevents that) b…

Summarized, I understand that you mean that a malfunction in the "reverse-thrust-detector" (which switches off automatically the involved engine(s) when the reverse-thrust is not operating within its envelope => referenced as "feature" below) is more desirable than not to have it? (because if, when having a mulfunction of the detector's "feature" in mid-air the engines switch off you still have some time to fix/overr…

Yes, no engines is bad but thrust reverser in flight is a instant killer.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#339

Post by esemor »

sandworm101 wrote: post #310
esemor wrote: post #189

I think the auto shutdown of engines in flight, in case it senses reverse thrust, is a great design. The 787 is a replacement for my 767 (currently a pilot on the aircraft) and in 1991 a Lauda Air 767 suffered a failure in one of its thrust reverser and it became activated during cruise. The aircraft was destroyed in flight. The thrust reversers should not activate during flight (a air/ground sensors prevents that) b…

Fyi, military pilot here, there are a handful of mil aircraft that can reverse thrust in flight. A great too for dropping down fast to avoid low/slow flight over hostile areas. There might be a relationship between that ability and this problem.

Lucky bastards, get all the fun features...

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#340

Post by kondro »

Rooster61 wrote: post #140

The second high-profile potentially deadly software caused failure related to automated safety features in as many years (if that ends up being the cause, of course). Very glad the touchdown went nominally. Had they pushed the point of touchdown just a bit further down the tarmac, they'd have skittered right off the pavement.

Skittered right into the arrestor bed:

https://en.wikipedia.org/wiki/Engineered_materials_arrestor_...

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