alt Hacker News>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.
> 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.
Well, those good old Boeing engineers and their management have misled the world more than once and no longer deserve the benefit of the doubt. That advisory is black-and-white, there is no arguing with what it says or does not say, you can read it for yourself. If your conclusion is the same as Boeing's then that's fine, you can have a different opinion. My conclusion is that if a load bearing component has these kind of potential issues that you need to act with an abundance of caution because of the price in case you get it wrong.
Yes, that bearing only moves a few degrees. But this is not about how much it moves, this is about what happens when it can not move and given the forces involved the outcome of that is fairly predictable, in spite of your previous statements. There is absolutely no way in which if that bearing is seized or otherwise constrained that this is safe.
> I would be very surprised if there weren't also maintenance failing of some sort here.
I explicitly left the door open for that. But regardless, this bearing should have never failed.
There are a couple of HN members whose pension depends on Boeing stock so I can see how this might ruffle some feathers but this is not a company that has behaved in a morally responsible way when it came to issues such as these om the past and you are effectively already blaming the maintenance people with your 'I would be very surprised if there weren't also maintenance failing of some sort here.'.
That is jumping to conclusions.
I would not be surprised if it were the case, but I also would not be surprised if it wasn't the case. That's the degree to which Boeing has squandered its erstwhile stellar reputation.
But, since you feel comfortable attacking my reputation from behind your shield of anonymity I suggest you flesh out your profile and Bio and tell us a bit about yourself and why you feel so emotionally involved in this.