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The headline is missing an important bit. Boeing knew of the flaw, and sent a letter to airlines about it. In 2011.
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.
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> 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.
As a matter of fact, the same issue did occur to US-based-airlines, and the pilots did catch it. That does not however answer the question of whether they just got lucky, or were more skilled, though there are some indications that it may have been skill.
There was an optional 'AOA disagree' system that an airline could buy that could help pilots know when the MCAS was going crazy. US airlines, perhaps having more money, may have bought those (helping pilots with situational awareness), but airlines in developing countries (with presumably less money) may not have gotten them.
See perhaps §6.4 about Boeing giving that functionality to everyone:
* https://www.faa.gov/sites/faa.gov/files/2022-08/737_RTS_Summ...
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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.
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> 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 lik…
The forces on that mount are pretty extreme. Once the bearing seized it was really a matter of time before something gave and given the strength of the casing as well as the strength of the material and mount points it was a toss-up between the bolts and the casing. The previous evidence showed a clear order to the bolts breaking suggesting one bolt was heavier loaded than the remaining ones. The new evidence points…
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Most likely just luck. These days US pilots can’t keep their planes separate from their helicopters so we're not exactly sending our best up there.
Mmmm…. Not saying us pilots are universally great, but I have definitely seen a significant regression from the mean in many foreign cohorts. I imagine it’s due to fundamental differences in the concept of training. It’s one of the things besides war that fear based societies seem to do better than shame based societies.
There is no way pilots form all over the world could "regress to the mean". They could not have been all, or most, "above the mean". The mean would be higher then.
I’m guessing that manufacturers know of lots of flaws in the parts they make.
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…
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I wonder on what basis Boeing thought that damage to a load-bearing part could be safely ignored? I hope it wasn't "nothing bad has happened for 50+ years, so it's unlikely to happen now"?
Usually this is because the design constraints are complex and in satisfying one you wind up having orders of magnitude more overkill than you need on others.
For example, in situations involving hollow shafts with through shafts or perhaps fluid passages often times you wind up with insanely huge for the load bearing supporting the outer most part because it simply needs to be that big in order to fit around the shaft and have space for reasonable sized roller elements for the speed and realistic race thicknesses, etc. Sure you could go custom, but $$, sure you could use needles or balls, but maybe the stuff on either side has reasons it shouldn't be hard like a race and that might add assembly/construction cost. Now say this overkill bearing is held up by a big web in a big honkin cast housing, because the housing needs to be like that for structural reasons (say it's a specialty pump or maybe this housing is load bearing in the overall assembly, like a tractor's gearbox). Now, say this bearing is in some more complex gearbox that has lubrication windage problems. A valid fix might be to go and cut out a chunk of the web that holds this bearing. Sure it's only supported by 300deg now instead of 360, but it was so overkill to begin with that doesn't matter.
Edit: better example: You can roach dozens of automotive cartridge style wheel bearings without hurting the knuckle it presses into because the knuckle has to be so strong to withstand suspension forces you basically can't apply enough force via the wheel failure to break it and the assembly becomes unserviceable faster than you can get to the point of damaging it by wearing through it.
Edit2: You also need to consider the cost of QA and testing. Sometimes it's cheaper to do a simple overkill waste of material design than something than to do speed holes and engineered webs, etc, etc, because all those features add testing cost as well as manufacturing cost and (especially in ye olden days of the slide rule) make it harder to predict stuff like resonance, exact failure mode, etc, etc and every feature has to be QA'd to some extent. And this all needs to be balanced against expected production volume.
Insane that we can have places like the skunk works create the sr71 and operate on shoe string budgets but the largest passenger plane company in the world can’t accurately assess risk on planes far under the former planes Mach 3 record
I don't see that as a valid comparison. SR-71s could operate with a much higher level of risk than commercial passenger planes. IIRC, SR-71s leaked fuel on the ground, and their wings dragged on the ground without special attachments. Pilots needed special pressure suits, etc. I also expect that they were much less complex than an aircraft that provides a comfortable, pressurized cabin; the high level of safety menti…
Earlier quoted context omitted.
The forces on that mount are pretty extreme. Once the bearing seized it was really a matter of time before something gave and given the strength of the casing as well as the strength of the material and mount points it was a toss-up between the bolts and the casing. The previous evidence showed a clear order to the bolts breaking suggesting one bolt was heavier loaded than the remaining ones. The new evidence points…
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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.