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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

#631

Post by kennethrc »

ethbr1 wrote: post #495
9659 wrote: post #464

Earlier quoted context omitted.

"Runaway stab trim". It is a memory item, every pilot should be able to perform it from memory. Turn off the motor, and the trim is manual. There is a crank right there in the cockpit. If it is too hard to turn, change aircraft configuration to reduce the forces required to. Pilot know how to do this. This pilot stuff, they understand the forces on the flight controls and what impacts them. Boeing made an engineering…

> 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…

One of which (Atlas Flight 3591) was Pilot error:

> The probable cause of this accident was the inappropriate response by the first officer as the pilot flying to an inadvertent activation of the go-around mode, which led to his spatial disorientation and nose-down control inputs that placed the airplane in a steep descent from which the crew did not recover.

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

#632

Post by Snow_Falls »

didntcheck wrote: post #619
matthewmacleod wrote: post #615

Earlier quoted context omitted.

“This aircraft failed because Boeing is too woke” is a pretty amazing take, I’ll grant you that.

"because they were prioritizing other factors instead of competency" That's not a particularly outlandish take, and the other factor is orthogonal

Do you believe that other factor is wokeness, or is it maximising profit

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

#633

Post by londons_explore »

Which is more likely:

* Lazy production line worker hand-tightens bolts and forgets to torque them, faking the results on the electronic torque wrench (which records the tightening of every bolt).

* A design flaw causes vibrations which cause these bolts to loosen.

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

#634

Post by nikanj »

londons_explore wrote: post #633

Which is more likely: * Lazy production line worker hand-tightens bolts and forgets to torque them, faking the results on the electronic torque wrench (which records the tightening of every bolt). * A design flaw causes vibrations which cause these bolts to loosen.

* A lazy/time-pressured worker skips applying threadlocker before assembly

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

#635

Post by justinjlynn »

nikanj wrote: post #634
londons_explore wrote: post #633

Which is more likely: * Lazy production line worker hand-tightens bolts and forgets to torque them, faking the results on the electronic torque wrench (which records the tightening of every bolt). * A design flaw causes vibrations which cause these bolts to loosen.

* A lazy/time-pressured worker skips applying threadlocker before assembly

Insufficient and negligent quality control systems design permits a single point of failure in manufacturing process specifically designed and funded to prevent such things - calling into question the trustworthiness of the manufacturing process compliance for the entire product line.

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

#636

Post by mywacaday »

rvba wrote: post #583
RF_Savage wrote: post #576

Earlier quoted context omitted.

The management imported from McDonnel-Douglas? The same management that drove it to ground? The fish rots from the head. And these constant problems sure do sound like a new company culture of cutting corners instead engineering first.

Looks like the installer did their job poorly and the QA rubber stamped it without checking. Are the QAs required to make photos to prove that they did their job? Like those food delivery people. Alternative is wrong bolts, or sabotage. But more possible - one lazy QA ghosting.

I would doubt one lazy QA, more likely a over worked and time short QA in a company culture that does not allow them to speak up when they need additional support.

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

#637

Post by stevehawk »

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.

ah. i've been wondering what the method of securing the bolts would have been and have not seen anyone mention it. torque values or threadlocker is rarely enough for the FAA. it's usually safety wire, castle nuts, lock washers, etc.

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

#638

Post by actionfromafar »

ethbr1 wrote: post #499
diabeetusman wrote: post #485

Earlier quoted context omitted.

Not sure why you’re bringing up autopilot— the MCAS system runs even when the autopilot is disabled. Edit: Also, how does the fault lie with the airlines? Boeing didn’t document the existence of MCAS in the flight manual or training materials.

Because the comment I was replying to >> Because the pilots should have been trained to unplug the computer to stop it from crashing the plane? Yes. The fault lies with the airlines because I don't for a second believe they didn't put pressure on Boeing to get the MAX certified without mandating retraining. And then once that was done, didn't dig into the details too hard about what changes were made. I have a low to…

It’s easier to blame Boeing because they made the damn thing its documentation. We know for a fact they are at fault. Some or all of the airlines may or may not have put pressure on Boeing.

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

#639

Post by sushibowl »

aredox wrote: post #621
kakwa_ wrote: post #592

Earlier quoted context omitted.

It's not necessarily a question of persons (and the CEO did a resigned after the Max crashes). It's more a question of culture (oversimplifying, sales vs engineering) and this is harder to change most of the time. Apparently, even the Max debacle was not enough.

The MD "moles" managed to change the culture of Boeing pretty quickly from engineering- to sales-first. https://www.theatlantic.com/ideas/archive/2019/11/how-boeing... https://archive.ph/vy5p7

Some of these executive quotes read (admittedly with the benefit of hindsight) like satire.

> But the nearest Boeing commercial-airplane assembly facility would be 1,700 miles away. The isolation was deliberate. “When the headquarters is located in proximity to a principal business—as ours was in Seattle—the corporate center is inevitably drawn into day-to-day business operations,” Condit explained at the time.

Oh man, wouldn't want that to happen.

> With ethics now front and center, Condit was forced out and replaced with Stonecipher, who promptly affirmed: “When people say I changed the culture of Boeing, that was the intent, so that it’s run like a business rather than a great engineering firm.”

Indeed.

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

#640

Post by arghwhat »

londons_explore wrote: post #633

Which is more likely: * Lazy production line worker hand-tightens bolts and forgets to torque them, faking the results on the electronic torque wrench (which records the tightening of every bolt). * A design flaw causes vibrations which cause these bolts to loosen.

Those are not the only options.

* Improper bolt tensioning process where bolt tension is later unintentionally reduced due to tensioning order.

* Design or material failure where bolt tension post-installation drops more than design allows.

* Miscalibrated or otherwise defective equipment.

* Other failure in manufacturing not caused by the worker, e.g. missed a necessary second or third tensioning pass (different torque or rotation angle) without appropriate failsafes or final validation to discover it.

Bolt tension validation is normally done with an ultra-sonic scan. Torque only provides a rough approximation of the tension at time of installation, and is only suitable where precision is not a requirement.

I suggest https://www.youtube.com/watch?v=XLzTB4KLCxU for those curious about bolts - a very specific, but interesting video.

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