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CGMthrowaway 3 hours ago

The headline is missing an important bit.

Boeing knew of the flaw, and sent a letter to airlines about it. In 2011.

rabidonrails 3 hours ago | parent | next [-]

Well yes but Boeing also said it "would not result in a safety of flight condition."

There's a lot of gray going on here.

autoexec 3 hours ago | parent | next [-]

A former air accident investigator who works as an aviation safety consultant said "It's extraordinary that Boeing concluded that a failure of this part would not have safety consequences," and said the report was "disturbing"

Doesn't seem like gray to me. It seems a company who has a history of cutting corners and ignoring or downplaying safety problems did exactly that in this case too which resulted in the deaths of many people. UPS made an error here as well in trusting Boeing when they said it wasn't a safety issue and they should have installed the revised bearing assembly out of an abundance of caution, but I don't know much they would have known back in 2011 about the changes at Boeing that prioritized profit over safety following the merger with McDonnell Douglas

somat 2 hours ago | parent | prev | next [-]

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 holding the engine on.

The best I can come up with is that a split bearing causes increased wear on the mounting bracket and nobody noticed for a long time.

Anyhow, here is the ntsb update in question https://www.ntsb.gov/investigations/Documents/DCA26MA024%20I...

jacquesm 2 hours ago | parent | next [-]

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.

ethbr1 18 minutes ago | parent [-]

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.

themafia 2 hours ago | parent | prev [-]

Juan Browne (blancolirio) breaks this down:

https://www.youtube.com/watch?v=q5OQzpilyag

ethbr1 24 minutes ago | parent [-]

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)

dralley 3 hours ago | parent | prev | next [-]

The FAA has not determined that this flaw did lead to a safety of flight condition. Investigation is still ongoing.

bombcar 2 hours ago | parent | prev | next [-]

Apparently they expected it to blow up on the ground, so technically the plane wasn't flying yet ...

hahahahhaah 3 hours ago | parent | prev [-]

Yeah saved boeing losing face and sales by requiring all the planes be grounded and fixed. Just eye it up every 5 years, if you want to.

WillPostForFood 2 hours ago | parent | prev [-]

FWIW, the MD-11 was designed by McDonnell Douglas, and manufactured by McDonnell Douglas in 1991, before the Boeing merger. A McDonnell Douglas DC-10 failed in a similar way in Chicago in 1979, so it the issue may go way back.

topspin 2 hours ago | parent [-]

AA Flight 191 in 1979, 273 dead. American Airlines invented their own engine removal procedure using a forklift and damaged a pylon and mounting bracket. The engine ripped off the wing on takeoff.

jsr0 an hour ago | parent [-]

Interestingly, the reason American Airlines was removing the engines (and pylons) in the first place was to replace that same aft bearing. McDonnell-Douglas had found that the aft bearing could wear out sooner than expected and issued a service bulletin requiring replacement. There is mention of it in the AA191 NTSB report[1] and also at Admiral Cloudberg's article on the accident[2].

[1] https://www.ntsb.gov/investigations/AccidentReports/Reports/... [2] https://admiralcloudberg.medium.com/rain-of-fire-falling-the...