United finds loose bolts on plug doors during 737 Max 9 inspections • Hacker News Board

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

#681

Post by MarkMarine » Tue, Jan 09, 2024, 2:08 PM UTC

stjohnswarts wrote: post #661

MarkMarine wrote: post #573

I was responsible for safe for flight inspections on military aircraft and the photo included in that post is completely insane to me. Those bolts being loose (and they are BIG bolts) would mean multiple people in the installation process didn’t do their jobs, and signed their life on the line saying they did. When I did maintenance, there was someone (QA) there to witness every torqued bolt, inspect every safety wir…

Did you torque every bolt every time before every flight?

Every bolt you could see was checked before every flight yes. Every important bolt you couldn’t see during inspection was torqued, witnessed by QA, secured via safety wire or cotter pin, and secondary torque holding was then inspected by QA.

This thing is obviously not just an interior part, look at the meat in those castings, and it’s obviously safety critical, look at the cotter pins on other bolts. Sounds like it was going to be installed behind interior paneling and not inspected every day. For something like that, every important bolt should be secured by secondary methods, torqued and witnessed installed correctly. This looks like a failure in engineering (not having wire on this bolts), then a profound failure in assembly with multiple people not doing their jobs (not torquing, not witnessing, faking logs), risking the lives of passengers.

If this happened at cruising altitude and speed, people would have died. I can’t find the flight number but I believe 9 people died when a jet lost cabin pressure and a piece of the plane while decompressing during cruising altitude over water.

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

#682

Post by drtgh » Tue, Jan 09, 2024, 2:13 PM UTC

SoftTalker wrote: post #548

unyttigfjelltol wrote: post #453

Earlier quoted context omitted.

The problem was software that prioritized input from a fauly external sensor, over pilot control, and literally crashed planes directly into the ground. At a certain step in the sequence it was not physically possible for a pilot to pull hard enough on the control element to counteract the software. Could they have disabled the system? Only if they could figure out the specific software trying to crash the plane. Is…

Pilots should (are supposed to) disable the auto-trim if it's doing something uncommanded/unexpected. Runaway trim can happen for reasons other than faulty software. MCAS was a new factor and they should have been told about it, I don't dispute that at all.

The manufacturer company put in larger engines than the aircraft is designed for. And they did it to avoid all the homologation licences and design costs involved in bringing a new aircraft to market with the appropriate tolerances, and to compete with another company's aircraft in time (Loss of sales).

They introduced MCAS in the aircraft for to balance by software a hardware issue, a big design negligent issue which can lead to stalling. It is beyond to trim an aircraft, and because of this there is a big difference in the scale of the values that the algorithm manages from a trimming.

It is not my field, but I think it is not a simple factor, and that it should not be put this over the Pilots like if it were a normal aircraft that received a simple update. Every pilot flying that plane should have been warned that it was not a classic plane with a classic update.

If this type of behaviour by aircraft manufacturers becomes the norm, costs over safety, we as passengers will suffer it, as other passengers unfortunately suffered it, while they blame the Pilots. In addition that nowadays the China's aircraft manufacturing industry wants to enter global market. Some days ago I read they want permission (homologations approvals) for to enter in the European Union.

PS: They also cut costs retiring backup sensors, delegating responsibility for a vital system due the MCAS to the buyer as if it was an unimportant feature; disaster was the order of the day. And the spending cuts were not limited to that, as we have seen in recent days.

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

#683

Post by ethbr1 » Tue, Jan 09, 2024, 2:14 PM UTC

WalterBright wrote: post #537

ethbr1 wrote: post #495

Earlier quoted context omitted.

> And that is how aviation becomes safer every year; at a significant cost of customers lives. "Significant" might be inaccurate. It looks like FAA Part 121 accidents over the last 10 years with fatalities have been... 4. [0] For a total of 6 fatalities. [0] https://www.ntsb.gov/Pages/AviationQueryV2.aspx ; 2018 (1 passenger fatality) https://www.ntsb.gov/investigations/Pages/DCA18MA142.aspx ; 2019 (3 crew fatalities…

That low accident rate is nigh inconceivable. It's an incredible achievement.

The fatal accident count is higher for GA, but I didn't normalize against flight hours or flights, just glanced at it.

I'm sure there's been a study somewhere that attempts to untangle all the factors that differ between commercial carriers and GA, to see which safety is most sensitive to -- continuous highly professional maintenance, highly trained and experienced crew, rigorous airliner certification regime, etc.

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

#684

Post by MarkMarine » Tue, Jan 09, 2024, 2:17 PM UTC

aredox wrote: post #622

gregoriol wrote: post #607

Earlier quoted context omitted.

Don't they have many ways to prevent bolts from unscrewing? I know at least a few by doing mechanical stuff on motorcycles, and it seems that other planes don't have such problems (at least not within 2 months after the last inspection).

There are washers, or thread lock glue, but it is still a question of correct execution: has the glue been applied? Was the glue batch used before its shelf life? Were the parts degreased before glue application? Or did anyone decided to cut corners by using an old batch/skipping degreasing/not putting glue because they were late on delivery?

safety wire and cotter pins are preferred methods on aircraft.

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

#685

Post by MarkMarine » Tue, Jan 09, 2024, 2:19 PM UTC

somewhereoutth wrote: post #625

whatever1 wrote: post #597

Earlier quoted context omitted.

Bolts can get unscrewed with vibrations. So probably a design error, they did not use the correct type of bolt (the one with the safety pin).

My understanding is that the bolts did have castle nuts and retaining wires in the design. So either they were incorrectly fitted, or the bolts themselves were under specified with regard to strength.

Those bolts aren’t drilled for safety wire.

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

#686

Post by NegativeLatency » Tue, Jan 09, 2024, 2:19 PM UTC

shmeeed wrote: post #590

NegativeLatency wrote: post #377

Earlier quoted context omitted.

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.

Where does one find a magnetic toothbrush?

It’s an old Sonicare brush head (a couple of fairly strong magnets are mounted to the bottom), there are also some kinda neat suction cup toothbrush holders you could use

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

#687

Post by legacynl » Tue, Jan 09, 2024, 2:24 PM UTC

amluto wrote: post #478

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…

> We have software QA departments that operate very much like manufacturing or aerospace QA. I don’t work in this industry, but this seems fairly ridiculous on its face: software is not at all like manufacturing. In manufacturing, there’s a design and a manufacturing process, and a critical function of QA is ensuring that the manufactured produce is manufactured to spec. With software, the software is written, compil…

> this seems fairly ridiculous on its face

I think that's why people always tell each other to not take things at face value.

Of course there is a big difference between sw and hw QA, in the thing that they test, and how they test them.

But they are also very similar. Any QA department has to think about ways that things can go wrong, and what things to test for, how to test, which testing methods, which standards to handle, keeping certifications, etc. During testing you also need to keep reevaluating if you actually are catching each problem/bug and how to implement changes in your company that decreases the amount of problems or increase the amount that you catch.

I think in that way there's a lot of overlap in thinking about business processes and how to identify problems with them.

Of course once a specific binary gets tested and approved by QA it shouldn't matter if it gets copied or whatever as long as you make sure its the same binary (by a checksum for example).

But still making sure that errors don't reach the customer, is vital in any QA. If errors does happen, QA is the department that can make sure that it doesn't happen again. And ofc be able to proof in court that you did your due diligence if something does happen.

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

#688

Post by boringg » Tue, Jan 09, 2024, 2:26 PM UTC

mc32 wrote: post #466

boringg wrote: post #460

Earlier quoted context omitted.

But all those communist airlines had no problems at all - exceptional build quality and operational efficiency! /S

Yep, Chernobyl being a prime example. Or Komarov's failed re-entry after complaining about the design faults of the vehicle long before launch. Then there was the more uhhm run of the mill backyard blast furnace campaign which contributed to misallocation of workforce which then led to mass starvation.

There are many many more examples. I find it so tiresome to see young people just use capitalism as a catch all for the failure of something. It's such a lazy and uninformed argument.

I'm not carte blanche defending capitalism - its a mixed bag but it sure outpaces the competing systems put forward to date. It does need some stronger safeguards against industry self regulation - that has a bad track record.

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

#689

Post by sgerenser » Tue, Jan 09, 2024, 2:41 PM UTC

irrational wrote: post #518

amluto wrote: post #478

Earlier quoted context omitted.

> We have software QA departments that operate very much like manufacturing or aerospace QA. I don’t work in this industry, but this seems fairly ridiculous on its face: software is not at all like manufacturing. In manufacturing, there’s a design and a manufacturing process, and a critical function of QA is ensuring that the manufactured produce is manufactured to spec. With software, the software is written, compil…

Ideally there should be a solid spec written and then qa can test against the spec. Maybe there is somewhere that does write solid specs, including accounting for corner cases, but in my 25 years working professionally in the industry, I’ve never seen it.

I work in software for CPU design/verification. Even here, where in theory there should be a rock-solid spec, there's not. There's a 12,000 page architectural specification, which is very helpful for specifying all the end-user visible state. But the microarchitectural specification is scattered all over different PDFs, visio docs, excel sheets, and sometimes the only spec is the RTL code itself.

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

#690

Post by x86x87 » Tue, Jan 09, 2024, 2:53 PM UTC

storf45 wrote: post #671

MarkMarine wrote: post #573

I was responsible for safe for flight inspections on military aircraft and the photo included in that post is completely insane to me. Those bolts being loose (and they are BIG bolts) would mean multiple people in the installation process didn’t do their jobs, and signed their life on the line saying they did. When I did maintenance, there was someone (QA) there to witness every torqued bolt, inspect every safety wir…

From when I worked as an engineer on the assembly line for smaller jets, know that there would be a record trail of exactly who completed the work, who signed off on it and what the work order steps were for anything related to these assemblies and components. This would include the work done at Boeing and their suppliers. Will be interesting to ultimately hear the root cause here.

Let me ask this: assuming they did not tighten the bolts correctly and qa didn't check it, what are the odds they keep an accurate paper trail?