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

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

#501

Post by bb88 »

9659 wrote: post #457
vegetablepotpie wrote: post #405

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…

About 2000, Software QA (and almost all traditional QA activities) were changed. The focus was on process over inspection. "Design in quality, do not inspect it into the product" Suppliers (to include software) were expected to manage the quality of the product they provided; the purchaser would focus on how they managed the process, not in the compliance of every part. This had a chance until software process was to…

Here's a stupid question: How do you know your process is good unless you inspect it?

"Hey Bob I know you're a competent engineer, but don't worry about specifying a certain type of bolt or loctite, the untrained assembly personnel will figure it out. I'm sure they won't let 200 people die in a plane crash."

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

#502

Post by ethbr1 »

Robotbeat wrote: post #474
ethbr1 wrote: post #371

Earlier quoted context omitted.

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.

I agree. I’m regularly critical of Boeing Defense (particularly space contracts where I’m a huge Boeing skeptic), but I think people are pretty off base if they think Boeing is just completely incompetent. Airliner safety is insanely good. Just vast seas of competence, but when there’s a super rare failure, the incorrect impression people get is that Boeing (or Airbus) is just full of incompetency. Almost nothing tha…

> Airliner safety is insanely good.

Because I dug it up for another comment, commercial carriers operating under Part 121 (roughly: scheduled passenger and cargo operation) had 4 fatal incidents in the last 10 years. [0]

Totalling 6 deaths.

In 10 years of US commercial carrier aviation.

One of those was literally 'the engine exploded and threw part of the turbine into the cabin (and also shredded some of the wing)'!!

Which resulted in 1 person dying and a successful landing.

[0] https://news.ycombinator.com/item?id=38921664

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

#503

Post by loeg »

deelowe wrote: post #467
heads wrote: 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…

A properly designed service manual will specific if the fastener should be lubed. If it doesn't say lube/thread locker should be used, then the fastener should be torqued dry.

In bicycle applications it is common to elide explicit instruction to use grease. Nevertheless it should be used.

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

#504

Post by bb88 »

vegetablepotpie wrote: post #456
ethbr1 wrote: post #420

Earlier quoted context omitted.

> Good software teams build quality into projects by introducing continuous integration, unit testing, creating feedback, and tightening these feedback loops. Agreed, for good software teams. I would content that most software teams at most companies are not good. Which is to ask, with an average to bad software team is it better to have integrated or separate QA?

Does it make sense to degrade the performance of good software teams because bad software teams exist? Ideally we’d always have good software teams, but in the real world sometimes you have to build software with bad teams. Leaders have options, they can do things like reduce scope, increase budget, increase schedule, or full on abandon or cancel the project. These are all options available to leaders, but they requi…

> Ideally we’d always have good software teams, but in the real world sometimes you have to build software with bad teams.

Here's a real, perhaps unexpected counterpoint. Say you have a good software team. How do they build good software with bad management?

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

#505

Post by jojobas »

sp332 wrote: post #433
nyokodo wrote: post #395

Earlier quoted context omitted.

> Evidently not though Bolts can be loosened by the physical and thermal stresses of use if there is a design flaw. So it’s not evidently an assembly QA problem.

The plane that lost a plug mid-flight was only two months old though. A design problem probably would have shown up in an older one.

Surely you've heard of reliability bath-tub curve.

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

#506

Post by FabHK »

rectang wrote: post #425
ethbr1 wrote: post #371

Earlier quoted context omitted.

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.

Is it plausible that Boeing has "learned" from software/startup/venture-capital culture with regards to tolerating higher risk to minimize costs? I suspect it's rather a case of parallel evolution between McDonnell Douglas brass and software startup culture, since cost-cutting culture goes back many decades (remember "Chainsaw" Al Dunlap[1] ?) — but I wonder if there's a more direct influence. [1] https://en.wikipedi…

Here's a Netflix documentary (in the wake of the MCAS crashes) that alleges that after the merger with McDonnell Douglas, the culture of the firm changed. Previously dominated by engineers, it was now dominated by MBAs with a focus on profit and shareholder value.

"With impressive clarity, Downfall: The Case Against Boeing reveals corporate corruption that's enraging in its callousness and frightening in its scope."

https://en.wikipedia.org/wiki/Downfall:_The_Case_Against_Boe... https://www.netflix.com/hk-en/title/81272421

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

#507

Post by johnwalkr »

jacquesm wrote: post #489
johnwalkr wrote: post #486

Earlier quoted context omitted.

It's a complex topic. Depending on the design, lubrication may be required or forbidden. And if it's required, it should normally be on the threads only, under the head is usually forbidden. And it's very important to understand that in most mechanical design with fasteners, the fasteners provide tension, and friction between 2 faces actually carries the load. Too little tension then fasteners can be sheared off. Too…

Lots of good stuff in this comment but I'm confused about the +/- 30% accuracy quote, in my experience it is relatively easy to reach sub 10% accuracy based on comparing different (good quality) torque wrenches against each other and against a calibrated one. Is there something I am missing here?

It's easy to calibrate torque wrenches to +/-5% of each other for _torque_. Calibrating a torque value to _tension_ of a fastener depends not only on the accuracy of the tool, but on materials, lubrication, temperature, process, etc. +/- 30% actually depends on having a good process. This only accounts for variations in tolerance, surface finish, etc. If you add lubricant under the fastener head when you are not supposed to, you can easily reach +50 or +100% tension.

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

#508

Post by shermantanktop »

vegetablepotpie wrote: post #405
ethbr1 wrote: post #371

Earlier quoted context omitted.

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.

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…

I’m going to be using “moral crumple zone” in every conversation I possibly can from now on.

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

#509

Post by Eisenstein »

Robotbeat wrote: post #474
ethbr1 wrote: post #371

Earlier quoted context omitted.

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.

I agree. I’m regularly critical of Boeing Defense (particularly space contracts where I’m a huge Boeing skeptic), but I think people are pretty off base if they think Boeing is just completely incompetent. Airliner safety is insanely good. Just vast seas of competence, but when there’s a super rare failure, the incorrect impression people get is that Boeing (or Airbus) is just full of incompetency. Almost nothing tha…

> It kind of annoys me when comment sections are filled with people talking about how incompetent Boeing is. It feels like out of shape slobs on their La-Z-boy chairs talking about how incompetent or slow some professional sports players are.

People do this with everything though, and air travel induces a large amount of fear in the populace. Not only are we not generally comfortable flying in the air for obvious reasons, but when it happens almost everyone has to concede control to a few people in the cockpit and on the ground. Driving, even if exponentially more dangerous, affords the illusion of control of one's outcome, given driving or having someone you know driving, and control over the vehicle maintenance, etc, as well as familiarity with the control and mechanism of the vehicle. These things don't exist with airplanes for the vast majority of people.

So, you can see why there is a need to find a human component to air travel problems, because that is something one can fix (fire the incompetent people, fine them, whatever), as opposed to all of the other things which must be accepted or rejected entirely.

It is entirely in line with human nature to do this, regardless of its accuracy or effectiveness.

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

#510

Post by unethical_ban »

mikewarot wrote: post #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 a…

I'll be charitable and assume you suggest "assets sold off" includes divisions to support existing planes and infrastructure.
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