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Boeing knew of flaw in part linked to UPS plane crash, NTSB report says

bbc.com

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Re: Boeing knew of flaw in part linked to UPS plane crash, NTSB report says

#41

Post by mrtksn »

benced wrote: post #39
mrtksn wrote: post #37

Earlier quoted context omitted.

I'm sure that a flaw in the plane can be handled more gracefully by the more skilled set of pilots however that's not the point really. Their point was that the flaw in the plane wasn't a big deal and the loss of life and equipment wasn't Boeing's fault, which wasn't true.

The reason we focus on the OEM more than the pilots is that Boeing getting its act together (or being regulated to do so) is more scalable than every pilot in the world becoming more skilled. Individually blaming pilots isn't effective , regardless of whether you're morally for or against it.

[flagged]

Re: Boeing knew of flaw in part linked to UPS plane crash, NTSB report says

#43

Post by ethbr1 »

themafia wrote: post #32
somat wrote: post #21

Earlier quoted context omitted.

I am wondering what the exact fail mode here is. Because my naive conclusion after looking at the part in question is exactly the same "would not result in a safety of flight condition." if the bearing cracked at the point in question it is going nowhere, the bearing is still captive in its housing. hell it looks like it could have been designed as two pieces and it would work the same. the large bolt is what is hold…

Juan Browne (blancolirio) breaks this down: https://www.youtube.com/watch?v=q5OQzpilyag

Deep link to the most relevant portion: https://www.youtube.com/watch?v=q5OQzpilyag&t=5m36s (spherical bearing cut-away diagram, actual bearing again, and failure mode explained)

Re: Boeing knew of flaw in part linked to UPS plane crash, NTSB report says

#44

Post by ethbr1 »

jacquesm wrote: post #22
somat wrote: post #21

Earlier quoted context omitted.

I am wondering what the exact fail mode here is. Because my naive conclusion after looking at the part in question is exactly the same "would not result in a safety of flight condition." if the bearing cracked at the point in question it is going nowhere, the bearing is still captive in its housing. hell it looks like it could have been designed as two pieces and it would work the same. the large bolt is what is hold…

That's indeed a very naive conclusion. Once that bearing is gone the stress that it would normally allow to escape on account of rotation would be directly transferred to the metal around it and to the bolts holding the whole thing in place. Guess what broke first? So if that bearing went that's not quite a smoking gun yet but it would definitely be a step closer to a root cause.

After watching the below video, it's the excess bearing play and thus no-longer-constrained force directions that would seem to be the issue.

With a proper tolerance bearing in place, the force is constrained so that other parts are only stressed in directions they're well suited to handle (because the bearing takes the load).

Once the bearing develops excess tolerance, you've got a bucking engine that (to your point) is directly loading other parts in unexpected ways/directions, eventually causing failure.

The fact that Boeing supposedly modeled this and came up with non-safety critical in the event of bearing breakage... curious how that will turn out.

Re: Boeing knew of flaw in part linked to UPS plane crash, NTSB report says

#45

Post by Dylan16807 »

mrtksn wrote: post #33
jacquesm wrote: post #5

I recall a lot of fingerpointing minutes after the crash by people blaming the presumably foreign maintenance crew. Even now there is a lot of uncertainty around this crash, maintenance - or lack thereof - or even wrong maintenance could still be a factor. But given the location of the part asking for a 'visual inspection' is a pretty strange move, the part is all but inaccessible when it is in its normal position an…

> blaming the presumably foreign maintenance crew The same happened with MCAS, the pro-Boeing argument was that if those were American pilots it would have been fine.

It's not really the same. Pilots need extensive training for how to handle emergency situations and maintenance crew don't. It's not super harsh to say that pilots in different regions are at different levels for those weird situations. It is super harsh to say that maintenance crews in some regions can't do their baseline job.

Re: Boeing knew of flaw in part linked to UPS plane crash, NTSB report says

#46

Post by mrtksn »

Dylan16807 wrote: post #45
mrtksn wrote: post #33

Earlier quoted context omitted.

> blaming the presumably foreign maintenance crew The same happened with MCAS, the pro-Boeing argument was that if those were American pilots it would have been fine.

It's not really the same. Pilots need extensive training for how to handle emergency situations and maintenance crew don't. It's not super harsh to say that pilots in different regions are at different levels for those weird situations. It is super harsh to say that maintenance crews in some regions can't do their baseline job.

That's entirely false, the maintenance crew are highly trained people they don't figure out things on the go and when they have to figure out solution to an issue, it's based on what they know about the aircrafts from their training.

Re: Boeing knew of flaw in part linked to UPS plane crash, NTSB report says

#47

Post by Dylan16807 »

mrtksn wrote: post #46
Dylan16807 wrote: post #45

Earlier quoted context omitted.

It's not really the same. Pilots need extensive training for how to handle emergency situations and maintenance crew don't. It's not super harsh to say that pilots in different regions are at different levels for those weird situations. It is super harsh to say that maintenance crews in some regions can't do their baseline job.

That's entirely false, the maintenance crew are highly trained people they don't figure out things on the go and when they have to figure out solution to an issue, it's based on what they know about the aircrafts from their training.

Maintenance crew are highly trained people that in strange situations can pause their work to figure out a fix and ask experts what to do.

Very different from how a pilot has to handle strange situations. Being ready for anything in an airborne plane without a pause button is so much harder, impossibly hard, and not every air authority tries as hard to reach the impossible.

Re: Boeing knew of flaw in part linked to UPS plane crash, NTSB report says

#48

Post by robocat »

jacquesm wrote: post #22
somat wrote: post #21

Earlier quoted context omitted.

I am wondering what the exact fail mode here is. Because my naive conclusion after looking at the part in question is exactly the same "would not result in a safety of flight condition." if the bearing cracked at the point in question it is going nowhere, the bearing is still captive in its housing. hell it looks like it could have been designed as two pieces and it would work the same. the large bolt is what is hold…

That's indeed a very naive conclusion. Once that bearing is gone the stress that it would normally allow to escape on account of rotation would be directly transferred to the metal around it and to the bolts holding the whole thing in place. Guess what broke first? So if that bearing went that's not quite a smoking gun yet but it would definitely be a step closer to a root cause.

> Once that bearing is gone the stress that it would normally allow to escape on account of rotation would be directly transferred to the metal around it

The bearing would have to sieze up and the bearing axle be locked to the race. There is some limit to rotational torque even with a siezed bearings.

Metaphor: arthritic joints are not smooth, but they will rotate if given enough torque.

From the images, it looks like the bearing had siezed. So presumably rotational vibration was transmitted to airframe and the vibration caused structural failure?

I'm assuming it is not an issue of extreme rotational torque causing the issue (and given it is a bearing the design is for very little torque there!)

IANAME (not a mech eng)

Re: Boeing knew of flaw in part linked to UPS plane crash, NTSB report says

#49

Post by anal_reactor »

mmooss wrote: post #19

Some are forgetting how risk in technology works: No technology is designed or operated without flaws; that's an absurd approach and impossible to implement. To reduce negative outcomes, we use risk management: assessing the likely lifetime cost of the flaw, and taking cost-effective measures to reduce the risk to an acceptable level. As a familiar example, redundant mass storage drives are much more cost-effective t…

Sure, but the problem is, Boeing is a company that has a proven record of lying about the flaws of their products. There's a huge difference between "shit, nobody thought this part would crack in this way" and "we knew someone would eventually die, but we realized that paying the damages in case this happens is cheaper than preventing the disaster in the first place".

Re: Boeing knew of flaw in part linked to UPS plane crash, NTSB report says

#50

Post by rwmj »

mrtksn wrote: post #41
benced wrote: post #39

Earlier quoted context omitted.

The reason we focus on the OEM more than the pilots is that Boeing getting its act together (or being regulated to do so) is more scalable than every pilot in the world becoming more skilled. Individually blaming pilots isn't effective , regardless of whether you're morally for or against it.

[flagged]

Pilots who don't know about systems that are not documented in the manual are dummies?
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