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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

#271

Post by mhh__ »

noir_lord wrote: post #207
mhh__ wrote: post #203

Earlier quoted context omitted.

Probably not cost effective as opposed to either making the software more resilient or just letting some monkeys/interns loose in the cockpit and pressing everything (With some focused searches obviously)

I don't know, I suspect software resiliency is one of those "gets exponentially more expensive as you approach perfect" situations and a robot could bash inputs at speeds a human couldn't in thousands of orders, it would certainly let you test those weird code paths that blow up when they are never exercised until they are.

It does get exponentially more expensive, which is why you have to pick a certain level of ~perfection~ and then stop.

Also, the robots would have to bash at the speed of a human: The point is to mimick human inputs not necessarily test every code path (Which you could do in software)

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#272

Post by mhh__ »

lallysingh wrote: post #270
mhh__ wrote: post #203

Earlier quoted context omitted.

Probably not cost effective as opposed to either making the software more resilient or just letting some monkeys/interns loose in the cockpit and pressing everything (With some focused searches obviously)

..or not requiring physical hardware to test?

How? Planes won't not have cockpits for decades surely.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#273

Post by salawat »

gugagore wrote: post #191
salawat wrote: post #184

Earlier quoted context omitted.

If the reverser could rip the engine off the wing, it wouldn't be safe to engage on the ground. Just thought that was worth pointing out. A reverser only redirects thrust, and only generates about 60% of max thrust pushing backwards. It's only on for a limited time on the ground because under a certain speed, you run the risk of blowing FOD into the intake path, putting the engine at risk. I'm not aware of any reason…

The cruising airspeed of an airplane is faster than its landing speed. I don't know if that alone is enough to rip the engine off the wing, but it's something that it sounds like you did not consider in making your point. [EDIT remove "roughly speaking an order of magnitude"]

The difference isn't that large in the grand scheme of things. The engine mount would have to be able to fail in it's operational envelope in order for the reverser kicking in to be realistic.

In fact, the reversed kicking in would decrease the loading on the aircraft by decreasing it's airspeed.

This isn't a case of acceleration being able to break the mount from the frame. If it ever could, one wouldn't want it on the plane in the first place.

Doesn't mean you couldn't ruin your day with it, but it isn't an instant catastrophic failure either.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#274

Post by weaksauce »

outworlder wrote: post #254
weaksauce wrote: post #222

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'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…

I think there are a few options for a failsafe here.

none where it would deploy the reverse thrusters and probably crash regardless of other inputs to the system(could be one or more of many inputs wheel speed, slats deployed, airspeed, elevation, throttle position, etc.)

turning off the engine (presumably you want this because you are on the ground but your ground sensor is failing so you want to cut engine and apply brakes which is less preferable than the reverse thrusters but manageable normally.)

ignoring the input altogether.

not a failsafe at all and an unexpected failure mode of the system (I think this is probably the case since they couldn't relight the engine on the ground)

the point i was making is that if you have the failsafe turn off the engines under normal operating procedures it should be able to relight when in flight and it's not good if a software glitch turns your heavy into a glider without possibility to relight. (i am not a pilot but it's my understanding that you still have the turbines spinning and all you need to do is give it some fuel and fire up both ignition plugs. might need to use the compressor to spin them up to full speed but i doubt it.)

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#275

Post by weaksauce »

astrodust wrote: post #258
weaksauce wrote: post #222

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.

Having altitude and being able to glide in is a hell of a lot better than one of your engines reversing and throwing your plane into an irrecoverable spin.

I agree and that's not what I meant I replied in another comment.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#276

Post by inferiorhuman »

dsfyu404ed wrote: post #206
blattimwind wrote: post #170

Earlier quoted context omitted.

Standard transmissions nowadays often include mechanical features as well that make it very difficult / impossible to engage reverse (and first gear) while going forwards at more than a few km/h.

Even a 1950s era transmission will still be very hard to force into a gear if the speed difference is too great. Likewise you'll have a very difficult time shifting into reverse or 1st at speed. That's just how syncros work. You might be able to overcome it by double clutching but it would require conscious effort. Even just shifting to reverse while rolling is difficult.

Still possible though. Years ago a friend and I pulled a manual transmission in a junk yard. He got it home, installed it, and then discovered reverse was completely stripped.

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#277

Post by CamperBob2 »

metalliqaz wrote: post #256
sbradford26 wrote: post #224

Earlier quoted context omitted.

Overspeed protection takes place once everything else has failed. The engine controls have already attempted to throttle down and such. If that doesn't work then overspeed kicks in.

Adding on to this... things inside an engine happen FAST. Too much energy can spin up the turbines to the point of failure in milliseconds.

Yep, as anyone who has ruined a fan by shooting a canned air duster at it can attest. :(

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#278

Post by stevehawk »

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?

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

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#279

Post by bigiain »

mhh__ wrote: post #203
noir_lord wrote: post #143

Earlier quoted context omitted.

Make me think about could we use a robot to fuzz physical inputs.

Probably not cost effective as opposed to either making the software more resilient or just letting some monkeys/interns loose in the cockpit and pressing everything (With some focused searches obviously)

I wonder if selling tickets to watch would offset that somewhat?

I'd pay quite a lot of money to camp out in the desert for a week watching fuzzing robots try to crash airliners...

Re: Boeing 787 Suffers Rare Dual Engine Failure on Landing

#280

Post by detaro »

DuskStar wrote: post #215
detaro wrote: post #97

Earlier quoted context omitted.

on flight before the crash . After which it was repaired, and sent on the fatal flight.

It was also repaired before the previous flight. It goes like this: several flights report problem maintenance "fixes" the problem next flight reports that another, worse problem has appeared - bad enough that regulators have now said that the plane was "not airworthy" during this flight maintenance "fixes" the problem final flight impacts ocean at high speed Your assertion is that since maintenance cleared the plane…

No, my claim merely was that the quote does not make the claim about the specific flight (although I didn't word it quite clearly). The findings about bad maintenance culture certainly suggest that the plane wasn't fixed properly.
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