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Pilot Who Hitched a Ride Saved Lion Air 737 on the Day Before Deadly Crash

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Re: Pilot Who Hitched a Ride Saved Lion Air 737 on the Day Before Deadly Crash

#161

Post by mehrdadn »

Diesel555 wrote: post #152
flashman wrote: post #23

So a single point of failure (malfunctioning sensor) can engage the horizontal stabilizer without notifying pilots, in a way that the control yoke can't override. What the hell did Boeing think was going to happen?

All fly by wire jets have movements based on sensors. In the F-16 a faulty AOA probe is okay. 2x Faulty AOA probes are okay as long as they disagree. 2x faulty AOA probes that agree (frozen) are a very bad thing. But the loss is just a jet with an ejected seat if it can't be fixed, not nearly 200 people which is terribly sad. The worst part is from a previous Hacker News post listed below. In particular, the "Economi…

> No 737MAX with this option has ever crashed.

I mean there are only two 737MAXes that have crashed in total, right? It's not like we have such a huge sample to work with for this to carry that much weight.

Re: Pilot Who Hitched a Ride Saved Lion Air 737 on the Day Before Deadly Crash

#162

Post by fegul »

spricket wrote: post #151
tntn wrote: post #148

Earlier quoted context omitted.

The checklist in question has three steps. Step two is "move stab trim to cutout," which disables automatic systems that adjust the stabilizer. The pilots in lion air had ~10 minutes to do this. It is extremely unlikely that the pilots were trying to work through the checklist. More likely they simply did not know what to do.

This doesn't make jive with disaster being averted by a third pilot. Assuming the third was totally dedicated to checklist vs preventing the plane from diving, it was only his insight that stopped the plane from going down. The MCAS system apparently increased downward trim without any speed considerations, to over 2.5 degrees in 10 seconds. I don't have the full flight control details but it sure sounds like pilots…

This "human" factor was also characterized in the movie Sully when it was apparent that just a few extra seconds for pilots to process the issue made all the difference between landing safely at a nearby airport vs. landing in the Hudson River.

Re: Pilot Who Hitched a Ride Saved Lion Air 737 on the Day Before Deadly Crash

#163

Post by cjbprime »

dsfyu404ed wrote: post #57
jimktrains2 wrote: post #53

Earlier quoted context omitted.

> That's east to say from an armchair but on an aircraft everything is "safety critical" to some extent and you have to choose what gets redundancy. In flight entertainment, non-emergency lighting, food prep, &c aren't "safety critical" any more than the TVs in hospital rooms are. As a layman, I'd've imagined that all avionics and control surface control was redundant. Don't most large planes have redundant hydraulic…

But this isn't really "avionics and surface control" more than automatic lane keeping is a critical control system for the car. MCAS is a convenience feature that counteracts the plane's tendency to pitch up more than you want when climbing. Sure it can improve safety, so can lane keeping in a car. Neither are critical to operation. You can fly/drive perfectly safely without them so they need not be super hardened ag…

I'm afraid everything you're saying is just very wrong:

> [Boeing self-assessed] a failure of the [MCAS] system as one level below “catastrophic.” But even that “hazardous” danger level should have precluded activation of the system based on input from a single sensor — and yet that’s how it was designed.

-- https://www.seattletimes.com/business/boeing-aerospace/faile...

Even at Boeing's understated safety risk, redundancy is required. And the system actually has much more risk than they stated, since it will eventually totally deflect the stabilizer -- as happened to both fatal flights, with the jackscrews found in their farthest position in the wrecks.

Re: Pilot Who Hitched a Ride Saved Lion Air 737 on the Day Before Deadly Crash

#164

Post by cjbprime »

tntn wrote: post #148
spricket wrote: post #141

The fact that "AoA disagree" light and logic was an optional feature seems criminal enough to me. A sensor with no failover unless you pay for an option. Who the hell thought this was a good idea or approved it? WTF! 500 people are already dead. Boeing should be brought to the coals. It probably takes longer to go through the checklist than it does for everyone to die. I promise if the audio recordings are ever relea…

The checklist in question has three steps. Step two is "move stab trim to cutout," which disables automatic systems that adjust the stabilizer. The pilots in lion air had ~10 minutes to do this. It is extremely unlikely that the pilots were trying to work through the checklist. More likely they simply did not know what to do.

This one's actually a memory item, not a checklist. But it's the memory item for "runaway trim", which is a very different qualitative experience than the slow march of an MCAS system that you didn't know existed.

Re: Pilot Who Hitched a Ride Saved Lion Air 737 on the Day Before Deadly Crash

#165

Post by snowwindwaves »

cjbprime wrote: post #155
Someone1234 wrote: post #94

Earlier quoted context omitted.

Boeing offered that, but it was a paid extra that few airlines purchased. https://theaircurrent.com/aviation-safety/southwest-airlines...

This is grossly overstating the optional feature. As I understand it, "AOA disagree" is a single light near the AoA indicator itself. It's not an explanation, or even an alert. It's not where anyone would reasonably look when trying to diagnose an uncommanded flight control problem.

When lights are normally not lit and one lights up a pilot or other machine or plant operator should take notice.

A detailed explanation should not be required since they should know what the different warning lights mean and what can cause them to be lit.

I personally would like to see a list of the airlines that bought the more expensive 737 max that included the additional safety features.

Re: Pilot Who Hitched a Ride Saved Lion Air 737 on the Day Before Deadly Crash

#166

Post by jagthebeetle »

abbadadda wrote: post #149

What are the odds this is completely fabricated by Boeing? Not saying I think this, but if it was a movie and this was a cover-up, this would be a great plot twist. I suppose I'm maybe just a little jaded from all the fake news these days.

There's a difference between jaded and cynical :) Not that I know the answer to your question any better. We'll have to wait for the HBO documentary.

To play devil's advocate anyway, as someone who has not been following this actively, I find this article to cement the idea in this reader's mind that a Boeing malfunction is involved in all three incidents. Is this even conclusively established? Would Boeing want this spin at this point?

The suggestion that an extra brain might randomly have averted two multi-fatal crashes and that this error mode has occurred at least three times seems like it would be a bit pyrrhic for the PR people at this juncture, no?

Re: Pilot Who Hitched a Ride Saved Lion Air 737 on the Day Before Deadly Crash

#167

Post by cjbprime »

mehrdadn wrote: post #161
Diesel555 wrote: post #152

Earlier quoted context omitted.

All fly by wire jets have movements based on sensors. In the F-16 a faulty AOA probe is okay. 2x Faulty AOA probes are okay as long as they disagree. 2x faulty AOA probes that agree (frozen) are a very bad thing. But the loss is just a jet with an ejected seat if it can't be fixed, not nearly 200 people which is terribly sad. The worst part is from a previous Hacker News post listed below. In particular, the "Economi…

> No 737MAX with this option has ever crashed. I mean there are only two 737MAXes that have crashed in total, right? It's not like we have such a huge sample to work with for this to carry that much weight.

And the only airlines that bought the option are North American, so we are immediately confounding with pilot training differences.

Re: Pilot Who Hitched a Ride Saved Lion Air 737 on the Day Before Deadly Crash

#168

Post by cryptonector »

cjbprime wrote: post #154
cryptonector wrote: post #135

Earlier quoted context omitted.

It also shows that pilot awareness (and therefore training) should have been sufficient. The key deficiency here was Boeing's. The agency not disclosing this detail is a problem too.

That.. sounds like the literal opposite of what it shows, no?

I think you misunderstood. Had the pilots been trained, they could have dealt with it -- that the off-duty pilot was able to shows it was possible to respond correctly, while that the others weren't shows the lack of training is a real problem.

Re: Pilot Who Hitched a Ride Saved Lion Air 737 on the Day Before Deadly Crash

#170

Post by cjbprime »

jquery wrote: post #158
WalterBright wrote: post #92

Earlier quoted context omitted.

I'd fly on a 737 MAX tomorrow. But I might ask the crew during boarding if they're familiar with the stab trim cutoff switches.

I've flown on a 737 MAX a couple times this year. Smooth, comfortable, quiet flight. Although the failure of the MCAS system has been catastrophic, fortunately for Boeing the fix doesn't seem difficult... make an extra AoA vane or two mandatory and add a warning if they disagree, and require MAX pilots to sim train an MCAS failure. The planes seem eminently airworthy, so far it appears they weren't brought down by an…

There's already two AoA vanes mandatory on every plane (even non-MAX planes). There is a warning if they disagree in the optional package that the North American airlines bought, but not any other airlines. The warning is not much of a warning, just a disagree light. It would have been impossible for the Lion Air pilots to benefit from this disagree light, because they didn't know that it was hooked up to a control surface and neither did any other pilots, it seems.

> The planes seem eminently airworthy

An uncontrolled nosedive caused by a single sensor failure is not in anyone's definition of airworthy. It must be fixed. This lack of airworthiness was not the pilots' fault.

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