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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

#561

Post by mint2 »

Scoundreller wrote: post #34
Syonyk wrote: 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.

A recent example of your points: Toyota recently had wheels literally falling off cars due to mistakes like those.

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

#562

Post by talldatethrow »

johnwalkr wrote: post #486
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…

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…

Ive been working on cars and motorcycles and everything else other than airplanes for almost 25 years now, from motor swaps to transmission rebuild and custom suspension. The only time I ever use is a torque wrench is on engine internals, or smaller fancy areas into aluminum. Everything else, over the years, you learn by feel.

You pay attention to the size of the bolt, the material it's going into, and it's overall job. Yes you'll mess it up a few times a long the way. Hopefully you're a lot more careful when you see that the cost of making a mistake is a difficult extraction or alteration of some sort. Personally, I think you'll run into bolt/thread failure 10x more from improper insertion, dirty threads, corrosion, and overall entropy than you will from over torquing once you learn a few early lessons.

I've done countless brake jobs, tire rotations, oil changes, spark plugs, valve cover gaskets, shock and bushing changes, without a torque wrench. I've yet to ever had a problem from it after going a little too hard when I was 16 yrs old and learning what bolts and materials can hold what.

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

#563

Post by onlyrealcuzzo »

nolok wrote: post #356
jasode wrote: post #41

I found it interesting that Boeing did proactively tell airlines to inspect 737 MAXs for a possible loose bolt in a different part of the plane (rudder section) at least 8 days before the January 5th event. Example story: https://www.reuters.com/business/aerospace-defense/boeing-ur... Unfortunately, Boeing did not know they had other issues with the plug door bolts.

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

It's a QA process better than almost every other industry in the world...

Sure, it failed, and it isn't perfect.

But planes have had a long track record of being absurdly safe.

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

#564

Post by shiroiuma »

fzingle wrote: post #552
vegetablepotpie wrote: post #456

Earlier quoted context omitted.

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…

> Does it make sense to degrade the performance of good software teams because bad software teams exist? Consider the classic statistic "most drivers think they are above average". I posit that the same is true of software teams, almost every team will self-assess as above average, i.e. good. Those teams will then imagine that, being good, they build quality into the process and very little verification QA is done. I…

I'm curious: in your many years of being a consultant to these bad teams, where the manager really thought they were top 20%, did you get a chance to talk to the rank-and-file team members, and did they paint a very different picture of the team health and software quality than their manager?

Also, did you run across any orgs where they basically refused to use a process like Agile, and instead just did ad-hoc coding, insisting that this was the best way since it worked just fine for them back when they were a 5-person startup?

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

#565

Post by _gabe_ »

cogwheel wrote: post #560
stickfigure wrote: post #546

Earlier quoted context omitted.

The only complete and precise specification of software is the code itself. If some other form of specification was complete, we would be able to auto-generate the code.

This is beside the point. The code specifies what the product _is_, not what it "should" be. If you ask for a word processor and I deliver a perfectly bug-free and feature-complete calculator would you really believe it lived up to spec?

This is also beside the point. I think both of you are trying to warn against the dangers that lie on both sides of this coin: people can invest too heavily in a specification and waste an enormous amount of time, and people can immediately jump into coding and code something that does not do what it was intended to do. Like with all things in life, there’s a balance between these two extremes that’s correct.

You need some level of specification so you know what you’re building, but you have to keep in mind that the final code defines what the behavior truly is. Sometimes, that behavior unintentionally becomes part of the specification because users begin to rely on it.

I do like the fact that you both used hyperbole to succinctly illustrate the dangers of veering too far in either direction though :)

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

#566

Post by ajmurmann »

ethbr1 wrote: post #420
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…

> 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?

If your devs aren't good what are the chances of your QA team being good enough to make up for their short comings? The dynamics laid out by the parent comment will just hit even harder. Your best bet is to enforce basic practices like continuous integration, coverage goals and maybe a coverage ratchet as a merge gate. Training and education on areas were the team is weak is also a must.

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

#567

Post by Danieru »

jojobas wrote: post #505
sp332 wrote: post #433

Earlier quoted context omitted.

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.

Uh, first part of the bath tub curve is driven by manufacturing defects... That's not a counter point at all.

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

#568

Post by fsh »

Robotbeat wrote: post #475
rectang wrote: post #425

Earlier quoted context omitted.

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…

Boeing Airliners are much safer now than before they merged with McDonnel-Douglas. (Because basically all airliners are.) And I say that as a regular Boeing critiquer.

The 737 NG from before the merger has a much better safety track record than the 737 MAX.

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

#569

Post by thatswrong0 »

notahacker wrote: post #360
aledalgrande wrote: post #262

Earlier quoted context omitted.

So Airbus has fault for a paint job? While they should do better, that sounds a lot safer than airplanes losing pieces or crashing down to me. > You'll hear more about Boeing than the rest of the industry put together because this is HN... That's not it.

> That's not it. I mean, it is. The Pratt & Whitney engine issue which is going to ground half the MAX's rival's aircraft for a year because a manufacturing fault makes the engine turbine blades liable to crack garnered two threads and zero comments (Boeing got more for a fun story about paper planes!). Airbus being found at fault but acquitted of involuntary manslaughter by a Paris court last year for the AF447 cras…

> Airbus being found at fault but acquitted of involuntary manslaughter by a Paris court last year for the AF447 crash (a 2009 mid air stall with a few MCAS parallels) passed without comment

“Company isn’t found criminally negligent in case where it pretty clearly wasn’t being criminally negligent” isn’t.. news.

I’d be _really_ curious to hear what you think the MCAS parallels are (besides both cases involving a sensor malfunction) if you think that’s news.

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