[WalterBright]

Remember that the previous Lion Air flight to the one that crashed also has uncommanded trim movement, and the pilots there simply shut it off with the cutoff switches and landed without difficulty.

The cutoff switches are there to deal with trim runaway, and there is training for that.

[cmurf]

The flight data publicly available for the three flights, shows rather different MCAS upset behavior in all three cases. They're remarkably similar compared to what you'd expect for a normal flight. But the oscillations in the JT 34 case were not nearly as aggressive as the other flights, no evidence mistrim happened, and in fact the JT 34 pilots didn't recognize it as mistrim, it was the jump pilot who reportedly recognized something (we don't know anything about his thought process so far publicly) and apparently made a recommendation to set stabilizer trim to cutoff.

Is there training for getting out of mistrim at low altitude without the benefit of electric trim? Is there training even for MCAS upset as distinguished from runaway trim? We already know there isn't a way to simulate angle of attack sensor failure induced MCAS upset, in MAX simulators. Exactly how was it demonstrated that MCAS upset looks like runaway trim? And how much faster it commands nose down compared to the typical runaway trim case?

[salawat]

>Is there training for getting out of mistrim at low altitude without the benefit of electric trim?

No.

>Is there training even for MCAS upset as distinguished from runaway trim?

No.

Remember, MCAS was dropped from the manual, and not included in the end training pilot's would be exposed to prior to being handed a MAX. It was nowhere in that presentation. That was covered in the 60 minutes expose.

https://youtu.be/QytfYyHmxtc

>Exactly how was it demonstrated that MCAS upset looks like runaway trim?

It wasn't. Take a look at the ET302 preliminary crash report. You'll see attached to it the documentation pages from Boeing even remotely related to MCAS. In fact...

https://flightsafety.org/wp-content/uploads/2019/04/Prelimin...

Check Page 30 for the memory item as written. The AD from Lion Air is in there too I think.

Note the condition description explicitly mentions a condition where uncommanded trim is running continuously.

Before the AD issued after the Lion Air crash, no one even knew MCAS was a thing.

[WalterBright]

> Note the condition description explicitly mentions a condition where uncommanded trim is running continuously.

The trim system repeatedly coming on and driving the nose down is runaway trim. The pilot already knows he's in trouble because the trim is running, and he's looking at the checklist on how to stop it. And there is the information on how to stop it. Getting hung up on the definition of "continuous" while the plane augers in is something a computer would do, not a human pilot.

Which is why airliners still have human pilots, not computers, in command.

[salawat]

I was going to comment earlier on something you posted but I wasn't sure it was the time Walter. But hey, here goes.

In reply to someone else you posted to the effect that

>if the trim goes uncommanded, that's runaway trim.

If there is anything I did take out of Langewiesche's article, it is that apparently for some subset of the human species, it appears that the mental optimization you and I are capable of connecting naturally (stab runaway on continuous uncommanded trim-reduces to-> stab runaway on any unaccountable trim), is not, in fact, completely natural to everyone.

I've come to realize I have a team member who is one of those people. I have to be very careful with instructions to them, almost like programming. If I handed him that piece of paper, then asked them whether a pulsing trim system demanded that procedure, I'm not willing to stake my life on him getting it. So life being what it is, I have started to take the possibility of someone being of that disposition into account more frequently.

I've been somewhat disappointed at how frequently I run into it. I'm not saying there is anything wrong with those type of people, just that I can't necessarily generalize the capability with enough confidence to be comfortable with the connection not being proven to be made without demonstrable proof in the form of a simulator session or two.

It's just not a given I'm capable of assuming away anymore. I've seen (and even been the unwitting subject of) too many counterexamples, albeit in less than life-threatening conditions.

I certainly couldn't wrap my mind around why they wouldn't have made the mental connection while actually successfully retrimming the plane. After several months of devoting a hell of a lot of mental cycles to meta-cognition though, I've found I have my own corpus of "Oh, what the hell, how did I not make that connection til now?" which has been the result of many years of habit building.

I think I realized this earlier on, but couldn't convincingly articulate it. It came previously from the idea of psychological anchoring, and it's effect on subsequent responses in the presence of priming. It's a fairly well researched phenomena, and network theory also suggests it's a near certainty that this type of inability to grok can happen if mentation is an emergent result of our internetworked mass of neural nets that is the gray stuff between our ears.

It's still one of those fuzzy hunchy sentiments though, so not really something worth writing a paper about.

[WalterBright]

I understand that people are different and process things differently. There's nothing wrong with them. But some people aren't suited to be pilots, and flight school is supposed to wash them out. I also don't believe that misinterpreting "continuous" was a factor in the crashes.

One failure scenario that can cause runaway trim is mechanical damage that causes an intermittent short circuit which can cause uncommanded trim. "Continuous" or intermittent, you're going to want to cut off the stab trim, as you would any dangerous piece of machinery that is randomly turning itself on and off.

I have a difficult time conceiving of concluding that "the trim is coming on randomly and pointing me at the ground, but since it's not continuous I'll just let it keep doing that rather than turning it off." I'm not a pilot, but I bet my response would be more like "Holeee phuck, wtf is wrong with the trim, it's going to kill us all! Turn it off! Turn it off!"

As I mentioned, I spent 3 years working on the 757 stab trim system for the 757. Although I didn't come up with the idea, the engineers who did said that's exactly why the cutoff switches are clearly labeled and within easy reach. They're for "the stab trim is possessed by demons trying to crash the plane, shut it off NOW!"

Interestingly, the emergency checklist says to turn off the autopilot first, and if that doesn't stop the trim, then shut off the trim. My tendency would be to stop the trim, then turn off the autopilot, and fly manually the rest of the trip.

For example, there was a crash some years ago where the pilots got an air pressure warning. They dug out the checklist, and started following the procedure. They passed out from hypoxia before getting very far through it.

The checklist was then changed so that the #1 item was "put on your oxygen mask". These things are all so obvious in hindsight, but sadly too much gets learned the hard way.

[crooked-v]

The cutoff switches stop the runaway, but MCAS could max out trim to the extent that it was literally physically impossible to correct manually without steeply descending to take aerodynamic load off the control surfaces. Doing this has obvious complications when it's only a few minutes after takeoff and the pilots are already struggling to maintain any altitude at all.