[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.