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...

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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 20 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.

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themafia 2 hours ago | parent | prev [-]

Juan Browne (blancolirio) breaks this down:

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

	▲	ethbr1 26 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)