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United finds loose bolts on plug doors during 737 Max 9 inspections

theaircurrent.com

441–450 of 773 posts

Re: United finds loose bolts on plug doors during 737 Max 9 inspections

#441

Why are there bolts and machine screws in use in the first place? The seating configurations for United and Alaska, the 2 major customers for this aircraft, don't require this plug-door feature. Structurally, for these large carriers, the plug door serves only as a fuselage weakness and failure point. Why don't they just rivet it permanently to the fuselage and make it non-functional? Per the diagrams shown, it's a c…

Saves Boeing money by manufacturing 1 frame

Yes, certainly. But the carriers could configure it to make it non-functional, since it serves no purpose for them. Or they could spec it as a rivet-it-shut option from Boeing. Just seems crazy to have this big failure point in the fuselage, adding to their maintenance costs, for a thing they don't even use.

Re: United finds loose bolts on plug doors during 737 Max 9 inspections

#442

Earlier quoted context omitted.

> these false door panels are not. It's not a control surface, but it is a "moving part." That's what's baffling to me, that they spent a lot of effort building this hinge and pin roller system, and designed the door to hinge open up to 15 degrees. It makes me wonder if there's maintenance procedures that at some point would require the operation of that door to successfully complete. Otherwise, the mechanism itself…

It's built to be an actual emergency exit. It needs to be usable depending on how many passengers the interior is configured for. So it has all of the door bits there. Maybe some parts like the emergency escape slide are not installed. e: I should be clear that it's not usable as an emergency exit, as configured by Alaska. However the operator could choose to activate it later and install a usable exit.

This is not correct. To the passengers, this just looks like another seat next to a window with a plug installed. It's not a door.

If there was a reconfiguration to a seating standard that required the extra exit, the plug would be removed and a proper door would be installed, with the associated interior pieces.

Re: United finds loose bolts on plug doors during 737 Max 9 inspections

#443

At what point do consumers en-masse refuse to fly on these aircraft, if ever? When there's a few more fatal crashes?

People are very bad at managing risk. Even with all this, a 737-NG is infinitely safer than getting in a car, and yet people drive every day. Getting into your sedan is several orders of magnitude riskier than a 737. You're far more likely to die en route to the airport.

Obviously that doesn't excuse Boeing, I'm just saying, by the numbers.

[edit] The US has 1.5 deaths per 100M passenger-miles driven. [1]

The 737 NG has hit 10,000,000 flight hours 5 year into operating. That should be around 500,000,000 miles flown. About 180 seats per plane makes that ~90B seat-miles. That's 0.0038 deaths per 100M seat-miles flown.

So the 737-NG models are about 400X safer per mile than a car.

The median American lives 17mi from an airport, so the safety break-even point is 13,600mi flown on a 737-NG, assuming your destination is also a median 17mi away from the airport. If you're flying less than 13,600mi on a given 737 one-way trip, you're more likely to die getting to and from the airport.

Unless my math is off. This is just napkin math.

[1] https://injuryfacts.nsc.org/motor-vehicle/historical-fatalit...

Re: United finds loose bolts on plug doors during 737 Max 9 inspections

#444
post #307

Bolts and machine screws are very interesting. One mistake I, an amateur bike mechanic, made for years was not greasing bolts properly before assembly. It sounds counterintuitive but without grease a bolt (or machine screw) will bind early with a high torque well before it is correctly tensioned lengthways. The torque is just a proxy for the tension and it is this tension which is needed to fasten your components tog…

I keep a toothbrush covered in grease for just this purpose. It’s also a magnetic one so I can stick it to stuff and it stays put.

> I keep a toothbrush covered in grease for just this purpose.

Speaking from personal experience, this is also useful for brushing a robot's teeth.

Re: United finds loose bolts on plug doors during 737 Max 9 inspections

#445
post #356

Earlier quoted context omitted.

Imagine the quality of the manufacturing and QA / final inspection to have that kind of issue.

Nope. It is most probably caused by operational stress - rudder assembly is moving, fuselage is also working (compression and decompression cycles on take off and landing, thermal expansion and compression). I bet they don't just put red Loctite on it to keep it from getting loose. My bet is design flaws, not manufacturing or QA. EDIT: I saw the pictures of bolts with pins and bolts without pins. The ones with pins c…

I don't know about you, but in my industry, "QA" also means extensive testing to ensure that part/assembly/etc doesn't break with expected operations. So, yeah, from where I'm standing, this was a QA problem. Something did not get checked or tested as it probably should have.

Re: United finds loose bolts on plug doors during 737 Max 9 inspections

#446

Earlier quoted context omitted.

I work in the defense industry, it’s very much like the aerospace industry in that we deal with human life as a consequence of our work. We have software QA departments that operate very much like manufacturing or aerospace QA. Software QA provides nothing of value to software development; having it as a dedicated function works against the overtly stated goals of the function and counterintuitively acts to degrade q…

It sounds like they are calling something QA but using it as a liability shield. It makes sense that you are upset about that, but naming something QA and having it do something else doesn't mean that QA as an effort is bad. It means that the people doing that are being deceptive.

Fair point, you are correct in your inference that there are some bad actors in my workplace. However, I’ll argue that the fundamental dynamics of bifurcating the responsibility of quality from software leads to a steady state where all QA departments end up as a liability shield given enough time.

This is driven by Pournelle's iron law of bureaucracy [1], which says that people who promote the bureaucracy rather than the mission of the bureaucracy will get promoted within the organization and come to dominate its decision making.

For example, in schools, administrators make more money than teachers. This is despite both groups having similar levels of education and intelligence. The reason for this is that administrators know the laws and regulations of the environment they’re working in and ensure the continuity of the organization. Despite not directly contributing to the organization’s stated mission of education, they are in charge of the organization and take more benefits from it.

Software QA has similar dynamics. A QA department may start out making good faith contributions to the organization. Eventually there are product failures, eventually leadership needs a scapegoat to show they’re doing something, and eventually QA takes the blame. People get moved, demoted, or fired. QA realizes its risk, and takes steps to mitigate it. They create a highly systematized workflow and process, adopt or introduce standards. Then assert that following process equates to good outcomes. When bad outcomes occur, they point to their strict adherence to following process as evidence of innocence.

If the process does not support the work or mission, that is a cost they are happy to impose on other functions to deal with. This is the final state until a system disruption happens.

[1] https://en.m.wikipedia.org/wiki/Jerry_Pournelle

Re: United finds loose bolts on plug doors during 737 Max 9 inspections

#447
At this point, I believe Boeing needs to suffer the corporate death penalty, because it no longer operates as a net benefit to the public. It needs to be dissolved, and its assets sold off. Criminal charges should be pursued to the maximum support of the law against all of the corporate officers.

Those in the FAA and other oversight agencies who failed to properly oversee them should also be prosecuted.

Failing the above, perhaps it's time to revive an apocryphal custom of the Romans. The engineer of a bridge was required to have his home below it, as a means of enticing them to make sure it was well constructed. We should require that Boeing board members, and their immediate family, only fly in Boeing planes of same variety sold to carry paying passengers.

Re: United finds loose bolts on plug doors during 737 Max 9 inspections

#448
post #371
post #356

Earlier quoted context omitted.

Imagine the quality of the manufacturing and QA / final inspection to have that kind of issue.

I expect even at its worst, software development could learn a lot from aircraft QA. Especially since most shops have pretty much tossed professional career QA out the window.

Would you pay at least 2x for your software to have couple more nines of reliability? I’m gonna guess that “no”. At places where it costs $$$ to have bugs shipped to the end customer (e.g phones) or where there’re regulatory requirements they still have dedicated qa.

Re: United finds loose bolts on plug doors during 737 Max 9 inspections

#449

Earlier quoted context omitted.

More rampant speculation! Some quotes from this article: https://www.reuters.com/business/aerospace-defense/spirit-ae... > As part of the production process, Spirit builds fuselages for 737s and sends them by train with the special door assembly “semi-rigged,” one of the people said. > “They are fitted but not completed," the person said. > At its Renton, Washington, plant, Boeing typically removes the pop-out, or no…

I’m no MBA or aerospace engineer, but why sub-contract the fuselage? I get subbing engines, since engine designs can be used on/adapted to other (possibly non-Boeing) airframes, hence opening up economies of scale, etc. But the fuselage is most of the plane by mass and integral to the design of everything else. If you don’t like making fuselages, maybe you should get out of the aircraft business. Was this just a unio…

>Was this just a union-busting thing?

Yes, and to lower compensation because Boeing’s benefits are probably better than Spirits, and so if Boeing wants to pay the people that make the fuselage less, then having them be employed by someone else helps them pass non discrimination testing for pre tax benefits offered to Boeing’s higher compensated employees.

Also, lower unemployment insurance premiums if they want to reduce the amount of labor they buy, since Spirit would be the one laying people off.

Re: United finds loose bolts on plug doors during 737 Max 9 inspections

#450
post #20

Earlier quoted context omitted.

No, it's as insane as it reads. It means people were careless and sloppy during assembly. Think of it like seeing "one cockroach in your kitchen." It's not one cockroach. You just haven't opened up the rest of the walls.

Or it means the torque specs were a little too low, or too high and stripped, or the bolt threading was defective/spec’d wrong. Or bad metallurgy. Or the spec didn’t specify which order to tighten the bolts, so which direction you go causes different outcomes. Lots of stuff is assembled consistently and carefully “wrong”, but as specified.

It could also mean their torque wrenches are not being properly calibrated and traced, and have become out of spec. Out of college I worked as a mechanical engineer at a torque testing firm. We made devices with high quality torque sensors which are calibrated against NIST certified weights every 3-6 months, and those sensors are supposed to be used to check every single torque wrench both before and after each work shift to ensure they are accurate. Someone could choose to ignore that process, if they were sloppily cutting costs.
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