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 and even with an endoscope it would be pretty hard to determine whether or not the part had weakened. That's just not going to show up visually until it is way too late unless the part has been especially prepared to announce the presence of hairline cracks.
You'd have to disassemble a good chunk of the wing to gain access to the part based on the pictures I've seen of how it all holds together when assembled.
The same happened with MCAS, the pro-Boeing argument was that if those were American pilots it would have been fine.
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...
I’m pretty sure no American airline had the same situation that the airlines with the crash had because they paid extra for the redundant AOA sensor.
The MCAS issue was a major issue, but the ultimate fundamental flaw was Boeing not including a redundant sensor (which is the one that was malfunctioning in the crashes) in the base package as they should have.
The inexplicably considered redundancy in this part an optional extra, and as far as I’m aware there were no US airlines that hadn’t taken the optional extra package.
There was no redundancy AOA sensor option for MCAS.
All the planes were built with two AOA sensors, with the original MCAS implementation only using data from 1 sensor.
Edit: I was misremembering. Both sensors were enabled on all planes and MCAS only used one at a time on all planes.
What was disabled, unless paid for, was software which displayed to the pilots that the 2 sensors were disagreeing, which would immediately have alerted them to what may have been wrong.
> According to Bjorn Fehrm, Aeronautical and Economic Analyst at Leeham News and Analysis, "A major contributor to the ultimate loss of JT610 is the missing AoA DISAGREE display on the pilots' displays."[109] > The software depended on the presence of the visual indicator software, a paid option that was not selected by most airlines.[110] For example, Air Canada, American Airlines and Westjet had purchased the disagree alert, while Air Canada and American Airlines also purchased, in addition, the AoA value indicator, and Lion Air had neither.[111][112] Boeing had determined that the defect was not critical to aircraft safety or operation, and an internal safety review board (SRB) corroborated Boeing's prior assessment and its initial plan to update the aircraft in 2020. Boeing did not disclose the defect to the FAA until November 2018, in the wake of the Lion Air crash.[113][114][115][116] Consequently, Southwest had informed pilots that its entire fleet of MAX 8 aircraft will receive the optional upgrades.[117][118] In March 2019, after the second accident of Ethiopian Airlines Flight 302, a Boeing representative told Inc. magazine, "Customers have been informed that AoA Disagree alert will become a standard feature on the 737 MAX. It can be retrofitted on previously delivered airplanes."[119]
https://en.wikipedia.org/wiki/Maneuvering_Characteristics_Au...
Boeing: Do you want a two line code which triggers a potentially life-saving warning when your flying sausage with wings has an important sensor malfunction?
Customer: Of course!
Boeing: That'll be $25K, thanks.
What a load of bullcrap. Full stop.
The crews of the two crashed 737Max were also well trained, skilled professionals.
That the US-based crews decided to re-engage the auto-pilot, and with that action, by sheer luck, managed to bypass the fatal MCAS issues, shows you exactly what it was: sheer luck.
These pilots reacted to a system malfunction of a system they hardly knew existed (thanks to Boeing's lies), that changed the aircraft subsystems behaviour in fundamental, undocumented ways compared to the previous generation of 737s, and that they were therefore not trained to handle. So skill differences did not enter the equation, luck did.
The choice was between doing the manual procedures they were trained to do to try to regain control, and the hail mary approach of re-engaging the autopilot wtith the hope the problem went away. With no time to do both. The crashed crews chose option 1, the US crews option 2.
there's a 1992 wrap up book on that: https://www.cambridge.org/core/journals/robotica/article/abs...
all a bit before Boston Dynamics.
This is like Tesla claiming that all crashes due to autopilot failures are driver faults because they are not properly trained... it is supposed to be a car driveable with a regular car license! If you need extra train to drive it properly, be explicit.
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.
Very different from how a pilot has to handle strange situations. Being ready for anything in an airborne plane without a pause button is so much harder, impossibly hard, and not every air authority tries as hard to reach the impossible.
This is not just filling out reports and looking at stuff, they're in no way comparable to your local garage mechanic (and not to dump on them either: they too have to deal with out of the ordinary situations).
The responsibility issues are the same as with the pilots as well, they fuck up people die.
Also what fraction of engine test cell use is for engine maintenance? Is it a big amount?
But if that kind of test goes wrong the main outcomes are "hit stop" and "oh no it's too late". An emergency like that is not where much of their expertise is needed, their expertise is in other parts of their job.
Its not always foreigners that are to blame; sometimes it is because a woman was driving or the woke mind virus and DEI quota blind, deaf, midgets were on shift that day.
The motivation for fingerpointing comes from the same place in all circumstances.
Boeing knew of the flaw, and sent a letter to airlines about it. In 2011.
There's a lot of gray going on here.
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
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...
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.
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.
They'd have to show at least one plane with a bearing gone that still flies as intended. I suggest we break one on purpose, put the full complement of Boeing execs on that plane to prove its safety given the alternative of retracting that statement.
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 like the bearing had siezed. So presumably rotational vibration was transmitted to airframe and the vibration caused structural failure?
I'm assuming it is not an issue of extreme rotational torque causing the issue (and given it is a bearing the design is for very little torque there!)
IANAME (not a mech eng)
As for your 'limit to rotational torque': seized bearings do not 'rotate if given enough torque' they will break right out of their casings and whatever those casings are surrounded by. The reason is that unlike your cartilage the bearings are orders of magnitude harder than the materials around them. For a bearing to seize indicates that the material has already deformed, you either catch it before the race goes or it will crack and after that all bets are quite literally off. I'm not aware of any design that would spec a bearing in a situation with such forces that would still happily work with that bearing replaced by a bushing welded to the shaft and the surrounding material even if it is statically in exactly the same position.
What you describe is a worn bearing with an excess of play, not a seized one, which tends to exhibit roughly the same characteristics as a welded joint with dissimilar materials.
Bearings are wear items, bearings that are worn or seized are something that should never ever happen in an aircraft, there is no way that this particular design would continue to function with sufficient margin if that bearing would fail. If not caught before it breaks the next flight is going to be a disaster. Take off in a fully loaded aircraft of this size puts extreme stress on the engine mounts. They are designed with all of their parts in working order, this is not a case of 'oh, we'll fix that the next time this craft is in for maintenance'. All parts of a plane that is certified as airworthy are supposed to be operating as originally specified.
The default assumption is that it all looked good during the last inspection and that the time between the failure occurring and the plane going down was short. If it was not that would be highly unexpected. But again, until the final report is in that's speculative, and if anything the people at the NTSB are scary good at getting to root causes.
>What you describe is a worn bearing with an excess of play, not a seized one, which tends to exhibit roughly the same characteristics as a welded joint with dissimilar materials.
>Bearings are wear items, bearings that are worn or seized are something that should never ever happen in an aircraft, there is no way that this particular design would continue to function with sufficient margin if that bearing would fail. If not caught before it breaks the next flight is going to be a disaster. Take off in a fully loaded aircraft of this size puts extreme stress on the engine mounts. They are designed with all of their parts in working order, this is not a case of 'oh, we'll fix that the next time this craft is in for maintenance'. All parts of a plane that is certified as airworthy are supposed to be operating as originally specified.
Have you ever dicked around with servicing stuff in an application that has a lot of bearing, plain or roller element? Because it sure doesn't sound like you have with the way you're talking. Words like "sized" and "deformed" are far less binary that your spherical cow assessment implies they are. 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. For bearings that are there to allow for misalignment/flex and only move a few degrees often times they simply flex the parent assembly if seized. I can't say what would be a reasonable failure mode for this assembly though because I didn't design it nor similar ones.
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. 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.
This is a highly nuanced technical topic. None of us have the full facts at our disposal. I think the degree to which you are up and down these comments peddling a very specific chain of causality and putting down anyone who even has the most narrow or nuanced suggestion that it might not be exactly as you suggest is indicative of a moral failing.
[1] https://www.ntsb.gov/investigations/AccidentReports/Reports/... [2] https://admiralcloudberg.medium.com/rain-of-fire-falling-the...
To reduce negative outcomes, we use risk management: assessing the likely lifetime cost of the flaw, and taking cost-effective measures to reduce the risk to an acceptable level. As a familiar example, redundant mass storage drives are much more cost-effective than high-reliability mass storage drives.
And the DC-10 was not decommissioned. It is, in fact, still in service.
https://www.flightglobal.com/safety/us-faa-broadens-md-11-gr...
Aviation rules are written by blood, you either follow them or you add a few more lines with your own blood.
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.
I am not an expert, however. Can metal fatigue be detected with such infrequent inspection?
[1]: https://en.wikipedia.org/wiki/Aircraft_maintenance_checks#AB...
On things like D check, the aircraft is essentially completely taken apart and inspected at that level typically taking 50,000 man hours and 6 month-1 year of time.
The article mentions the cost and that Boeing underestimates it. When you divide the cost by the number of hours, it seems very reasonable. Parts and materials being included. I’m surprised any job that extensive isn’t even more expensive.
It was also insanely expensive to operate: $300k/hour in 1990 dollars, and there aren’t reliable numbers on development costs with all of the black budgets.
I know satellites and drones have replaced the sr71 but it would be cool if someone would build a plane as capable again.
I also expect that they were much less complex than an aircraft that provides a comfortable, pressurized cabin; the high level of safety mentioned above; freight capacity; etc.
Also, despite Boeing's recent problems, I would guess that commerical passenger planes are far more safe than they were decades ago when the SR-71 was developed. Accidents were much more common despite many fewer flights, iirc.
Obviously they could have designed something that could expand and contract if they thought it was worth it.
Also, this was done because airframe skin temps exceeded 400F during flight due to the high speeds.