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0 pointsWalterBright1y ago0 comments

> The damning part of it is that they were likely wrong for the reason of increasing profit.

Are you still advocating designing a whole new airframe instead?

> we still have to acknowledge it's not the best solution

We don't have to agree on that at all. It's an inherently simple solution, although Boeing made mistakes in its implementation.

> Just because a mitigation works some of the time

It's turning off a switch. The purpose of that switch is supposed to be a "memory item", meaning the crew should not need to consult a checklist. The switch is for dealing with runaway stab trim. Reading the step-by-step of the crisis, it is impossible for me to believe that the pilots did not know they had a runaway trim problem. There are two wheels on the side of the console, painted black and white, that spin when the trim runs, making a loud clack-clack sound. They are physically connected to the stab trim jackscrew with a cable. If the trim motor fails, the crew can manually turn the jackscrew via those wheels.

> You are advocating against well-established best practices in safety and reliability

Turning off a system that is adversely working is well-established in aviation. It's quite effective.

> and argue the points rather than appealing to (relatively weak) authority

Appeal to authority is not a fallacy when one has some authority :-) And so it is fair to list what makes one an authority.

> This isn't a pissing contest

You might want to review the condescending and quite rude post you wrote that I replied to. Your reply here is also rather rude. I don't think I've been rude to you.

Thank you for listing your credentials.

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bumby1y ago

>Are you still advocating designing a whole new airframe instead?

That would be the ideal solution for that hazard. But I can’t say if it’s the best risk profile overall. I would settle for a properly implemented engineered mitigation of MCAS.

>* It’s an inherently simple solution*

The fact that the engineers who built the thing mischaracterized it would seemingly be evidence to the contrary. I have experienced this flawed thinking often, where software is treated as a quick simple solution without considering the effects on the overall system.

>Appeal to authority is not a fallacy when one has some authority

It actually is. As Carl Sagan said, “mistrust arguments from authority.” But regardless, we seem to have different ideas on what makes someone an “authority”. You may be an aerospace authority when you’re in a room of CRUD software developers, but this forum has a much wider net than that. “Technical authority” is an actual assigned title at NASA, and you probably wouldn’t get it with 3 years of experience from decades prior.

“Turning off a switch” is the easy solution when you’re dealing with the benefit of hindsight. The pilots were operating in a completely different different environment. That’s why administrative mitigations are not a favored approach. Boeing simulator results demonstrate that it was a confusing scenario to identify the correct root cause in a time-critical situation.

As to the tone of the post, I’ve witnessed you in many aero circumstances state your credentials as a “I know what what I’m talking about so that’s the end of it” puffery tone. It in itself comes across as condescending and, worse, adds little to the conversation. I generally try to be respectful on these forums until someone shows they aren’t reciprocating. Normally I just roll my eyes and move on. I’ll give you the benefit of the doubt and assume you don’t even realize the condescending tone some of your posts take. I debated even responding but thought it might make you realize how off-putting you’re style can be. In your case, it comes across as very arrogant rather than curious which is contrary to the HN guidelines. If it offended you, I apologize.

WalterBrightOP1y ago

I admit to being arrogant, perhaps that's an inevitable side effect of being confident. When proven wrong, however, which has happened on HN (!) I try to admit it. I don't like making mistakes.

I'm not offended, as that's to be expected when I write things that are unpopular.

But I still accept your apology, and no worries. Perhaps we can engage again in the future!

P.S. I know about the simulator issues, but the information came filtered through a journalist and I am skeptical. What I cannot reconcile is the first incident where the deadhead pilot simply turned off the switch, compared with the simulator pilot. It didn't matter whether the runaway trim was the root cause. It did matter that runaway trim will kill you and it must be stopped. All three crews knew that, which is why they fought it.

In my work on the stab trim system, it was accepted that the first resort for trim failure was turning the thing off. Overhead in the 757 is a matrix of circuit breakers, the purpose of each is to turn off a malfunctioning system. The stab trim one, being critical, isn't located overhead but right there on the console.

I work with machinery all the time. When it fails, my first reflex is to always turn it off. For example, one day I smelled smoke. Looking around, smoke was coming out of my computer box. I could see fire through the grille. The very first thing I did was yank the plug out of the wall, the second was to take the box outside. The flames went out when the current was removed.

I simply do not understand failing to turn off a runaway trim system. Especially when it kept coming back on after normal trim was restored.

For another example, an engine fire. I don't know what the fire checklist says, but I bet right at the top it says to activate the fire extinguishers and cut off the fuel and electric power to the engine. I've done the same for an engine fire in my car :-)

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