alt Hacker NewsI owned a machine shop, and I'm the founder of a mid sized CNC gear factory. I think I know my way around bearings, lubrication, press fits and other such bits & pieces.
As for the rest of your comment:
What a load of tripe.
I'm doing the exact opposite of what you claim. I am just taking the bits of evidence already available and rejecting root causes that would require those bits of evidence to not exist, which is entirely valid, this still leaves a massive amount of uncertainty which I have underlined on more than one occasion.
Your suggestion:
> "A bearing that fails for whatever reason, welds it self, and then gets spun around in the bore by its shaft is nowhere near unheard of"
is not compatible with what reputable operators of airliners would expect from their gear and if it happens as a rule people die and the NTSB gets involved, see TFA. This is not just any bearing and this is not your average bench top, industrial or vehicular application, this is an aircraft and a major load bearing component in that aircraft.
> Unless you personally designed the mount of have insider knowledge of comparable ones you are speaking with degrees of certainty that are indicative of ignorance so massive it is functionally malice.
I think that's worth a flag, especially coming from an anonymous potato.
> The BS about how aircraft don't fly with worn bearings is just that, bullshit. Everything has service limits that allow degrees of wear. Now on some parts it might be zero or specific preload, but all that stuff is well defined.
Yes, there is 'acceptable wear over the lifespan of a part' and then there is 'worn out'. Bearings in aircraft are replaced well before they are 'worn out'. Don't conflate design life wear with excessive wear to the point that a part can no longer function.
>I owned a machine shop, and I'm the founder of a mid sized CNC gear factory. I think I know my way around bearings, lubrication, press fits and other such bits & pieces.
Then you have no excuse for having such a nuance free opinion for you must know things are often not obvious at "first glance of pictures someone else took" which is what we're all doing here.
>I'm doing the exact opposite of what you claim. I am just taking the bits of evidence already available and rejecting root causes that would require those bits of evidence to not exist, which is entirely valid, this still leaves a massive amount of uncertainty which I have underlined on more than one occasion.
I disagree. You are acting like this is a cut and dry situation wherein the Boeing advice that this was not safety critical is just wrong on it's face. That assessment was made 15yr ago (perhaps by "old good boeing" engineers) and on a part already under a lot of scrutiny from the other MD11 that lost an engine. Sure they could be wrong, but I wouldn't bet on it so confidently.
This bearing moves a few degrees. It's not like the engine is doing loops around the pylon. It's possible that for whatever reason the bearing stopped doing bearing things as well as it should. Now, this is a plane, everything is light, aluminum and made to flex to varying degrees. It's hard to say where exactly the movement was taking place in lieu of the bearing. Without specific knowledge it's hard to say how the failure happened. Maybe things got loose and failed from stress concentration. Maybe the movement happened in the wing assembly and the force+vibration of making that happen caused the engine mount to fail. You don't know. I don't know. Nobody in these comments know with a sufficiently low chance of being wrong to point the finger in any one direction.
To act like "well of course when the bearing wore/failed/whatever it ripped its mount right in two because now the force was concentrated and the part it was concentrated on was sus to begin with" is to confidently oversimplify the situation.
Engine pylons, landing gear, control surfaces, these are key systems, not the "built to within an inch of their life because they gotta be light" like a lot of other things on an airliner (though I admit the MD11 is a particularly questionable application of this heuristic)
Big planes generally don't fall out of the sky because one party misleadingly labeled something in the service literature. I would be very surprised if there weren't also maintenance failing of some sort here.