Comment by asynchronous13 | Hacker News Reader

Comment by asynchronous13 | Hacker News Reader

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> But it's crazy how many, when they're actually faced with catastrophic failure, forget how to fly the damn plane.

Your comment makes me sad. Especially since there will be many other people who come to a similar conclusion without adequate information.

The runaway trim problem and the new MCAS problem are superficially similar, but the symptoms are distinctly different. The runaway trim manifests itself with a continuous deflection of the trim. Pilots are trained to recognize this symptom and compensate. The new MCAS also affects the trim, but it is engaged in repeated nose-down commands. It has fundamentally different symptoms compared to the older and more widely known runaway condition.

There is no absolute reference on the position of the stabilizer. It is a wheel that turns, so a pilot must watch that wheel continuously to know if it keeps turning or if it turns periodically.

The controls column has force feedback. The pilot was pulling back with ~50 lbs of force to fight the angle of the trim. Imagine holding a 50 lb dog while simultaneously trying to review emergency procedures to find the source of the problem. The pilot was flying the damn plane, and the symptoms of this problem were different.

> There is no absolute reference on the position of the stabilizer.

There’s an indicator right next to the wheel:

https://qph.fs.quoracdn.net/main-qimg-1dc99dbe662c71d7c470cf...

And the pilots must have recognized it was a trim issue because they countered it multiple times. Why they didn’t flip the stab trim cut off switch is a mystery.

An earlier crew was able to fly the plane. I agree the pilots should have been made aware of MCAS (though either the Ethiopian pilot was shockingly not aware of it or being aware didn’t help him). But at the end of the day the pilots are there to fly the plane, not manage automation:

https://vimeo.com/159496346

The earlier crew faced an identical issue the day before, and it was only the deadhead pilot onboard who recognized the issue and suggested flipping the stab trim cut off. Out of 5 pilots (7 if we count the other crash), only one suggested the correct fix.

> Why they didn’t flip the stab trim cut off switch is a mystery.

Not really. In the previous incarnations of the 737, a hard pull on the yolk by a pilot disengaged the automatic trim system. In the 737 MAX, the yolk pull method to disengaged the trim was disabled. What the pilots did would have worked on the previous version of the plane, but not on the MAX.

Boeing really tried to claim that the MAX was just like the previous version, and that pilots didn't need new training to fly it. I think the data shows that more pilot training is appropriate for this plane.

> The earlier crew faced an identical issue the day before, and it was only the deadhead pilot onboard who recognized the issue and suggested flipping the stab trim cut off. Out of 5 pilots (7 if we count the other crash), only one suggested the correct fix.

And there are two ways to look at that. One is to say "obviously this means that this failure mode is too hard to diagnose". Another is to say "holy shit Lion Air pilots are fucking incompetent, I'm never going to fly any sort of third world budget airline if any of them are like this".

The truth is probably somewhere in the middle, of course.

> What the pilots did would have worked on the previous version of the plane, but not on the MAX.

And yet the checklist continues past that point, because guess what? The "control inputs disengage trim" component can also fail, and Boeing planned for that.

I believe you're right that the truth is in the middle. It really points to the pilots being inadequately trained on this aircraft. Boeing strongly pushed to avoid requiring new pilot training for the MAX airplane. They claimed that MAX was similar enough to the previous version of the 737 that if a pilot were checked out on the previous plane they were good to go. What we're seeing now is that assessment was wrong. More training should have been required.

Boeing fucked up big time on this one. FAA also fucked up. Pilots were inadequately trained, and some delivered info was false (Boeing said MCAS could only bring the nose down 0.6 degrees, in fact, it was unbounded)

The MCAS system was designated "hazardous" by Boeing in their own safety assessment. A system that is labeled hazardous can not be reliant on a single system failure. MCAS is reliant on a single sensor. That's already a major error in the safety analyses. As we can clearly see from two accidents, MCAS system should have been designated "catastrophic", one step more dangerous in that scale, with even more stringent redundancy requirements.

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