The Lion Air crews DID NOT KNOW how many units or even how long this goblin would trim. They didn't even have 10 seconds to observe the trim wheel amidst all the warning. To them, what happened to AC was exactly like what was reported/read in the pre-flight briefing: "STS running the wrong direction due to speed difference". As reported on the Lion Air's A-SHOR:

The conflicting data's [ALL INDICATORS were out of whack - previous flight at least the SIC's indicators were still valid, but not this one], perhaps observing the surrounding, rummaging through the QRH, communicating with the ATC, etc..., were all conspiring to overload their mental faculties and sensory perception. And, to top things off, they didn't have the luxury of having a dead head sitting on the jump seat helping to observe and analyze what's going on.

On the preliminary report, CAPT and/or FO of the previous flight apparently had failed to mention the stick-shaker condition and the NNC for runaway trim they'd performed to overcome what thought to be the STS trim going the wrong way. The last few facts are very much what makes the hole in the Swiss cheese lined up.

I'm thinking that the JT610 P1 retrimmed completely from each MCAS excursion, but P2 did not allowing the nose down trim excursions from MCAS to accumulate while P1 was head down in the manual - which had no information on MCAS.

​​​​​​Will the CVR, once released, show whether P1 communicated to P2 what P1 was doing with trim before handing over control?

Remember also that stick shaker was adding workload.

We now know that a faulty AoA will both trigger shaker and MCAS once at a safe height where flaps are normally retracted and more thorough diagnosis of the situation can begin, but then they were handed a new problem.

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Yes recognizing the trim issue is the heart of the matter. That was exactly my point. You cannot make this into "switch off the AP and fly the plane"-scenario. A pilot with poor manual flying skills but being able to identify the issue does much better than a skilled flier who isn't able to identify the issue.

It doesn't help you to switch off AP and AT and stabilize things by flying "power and pitch". You can't because you don't achieve a stable pitch.

So hence my real point, the challenge: Show me that up until six months ago anyone suggested making "stab trim cutout" part of a "disengage auto and fly the plane" if you don't have a clue what the issue is.

The "should they have been able to catch on to the trim issue?" discussion has been done ad nauseam. In my personal opinion the only way to hypothetically get the truth there would be if you could find 20 average pilots who had been in coma for the last six months and put them through a surprise sim scenario replicating an actual MCAS-misfire.
Then we would know how the average pilot would have done.What people with all the facts are now convinced they would have done is not relevant evidence to me.

I bet that if you asked the average px if they were confident that they'd get a life jacket on in case of a water landing landing the vast majority would say yes. They've seen the briefing a gazzillion times. How hard can it be?

Yet we know how many out of a 150 px in the "Sully flight" actually managed to put on a life jacket properly waist strap and all. Was it a three digit number? Was it a two digit number?

Having read every post since the first crash I'm at a loss as to how we're not, for the most part, progressing logical thought.

To see this 'Why didn't they fly the plane'. chanted out again and again is beyond offensive. The congressman has "been in contact with . . ." etc., etc. I'm sure he would have handled the MAX like a Warbird, and saved the day.

For the first time in many, many years on PPRuNe, I'm allowing myself to really bristle at some of the posts.

There are so many factors coming out of the woodwork. The Seattle Times was the first to spell out some of the home truths. The technical article today left me astonished. The rear switch (in the column) removed, and the function of the left and right Stabilizer cut out switches changed in the MAX. ??? Have I missed these points? Are they not correct? They're major factors.

'gums' has a lot of experience and his considered thoughts today about being in the hot seat for those first moments says a lot. Mostly, the problem was NOT bloody obvious, it was, insidious - proceeding in a gradual, subtle way, but with very harmful effects. A word I chose carefully in one of my earlier posts.

The LEFT/CAPT shaker was triggered immediately, IAS/ALT disagreed as well. Meanwhile, MCAS trim was activated after the AC was flap up.

Salute!

Apparently the Chuck Yeager cadre here lives on....
So today we see other examples:
Beam me up.

Gums sends...

It's said that angle of attack disagree was 22°5 (at least on Lion Air). But the AoA vane does not directly measure angle of attack, but angle of airflow around the fuselage, which is higher - about twice the angle of attack - due to aerodynamics around a long body

That means the error at the Angle of Airflow vane was not 22°5 but about 45°, which correspond to the angle between AoA screws.

"Much like tapping the brake pedal in a car to disengage cruise control, a sharp tug on the controls of older models of Boeing Co’s 737 used to shut off an automatic trim system that keeps the plane flying level, giving the pilot control.

But Boeing disabled the “yoke jerk” function when it brought out the 737 MAX, the latest version of its top-selling jet - and many pilots were unaware of the change, aviation experts told Reuters....

...pilots would have needed to know that MCAS existed, that it had unusual power to force the plane down and that “a hard pull on the yoke” would no longer turn off the automatic trim that uses MCAS, John Hansman, an aeronautics professor at MIT, said in an interview.

“That wasn’t clear to the pilots flying the airplane,” Hansman said. “The training material was not clear on that.”"


https://www.reuters.com/article/us-e...-idUSKCN1R322M

Towhee:

So it seems that rear switch in the pole has been removed on the MAX.

That is a major difference. I wonder if it was mentioned in the few minutes of conversion notes.

TowerDog:

Well, that's the point. If. As in, If you know it's happening.

First and foremost: it's not a stab trim runaway in the usual sense. The inputs, resets and then re-datumizing is quite, quite different. Plus you're in a chaotic condition before 1000' and flaps up.

Remember, you observe the STS running on a daily basis, and the MCAS actions are so intermittent and subtle that you don't know there's something inputting into the Horizontal Stabilizer from that source. You're not going to be able to diagnose what's happening while under stress - especially if you've never been told there's a software system that's taking this mysterious action.
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I don't believe I really get this point. It sounds OK if indeed the airflow was not parallel with the fuselage at some locations. But why wouldn't the streamline effects be well known beforehand from wind tunnel testing and the AOA vanes located at a point where the lines are truly parallel?

Are you suggesting the AOA sensor was installed 45° from the proper angle? Is that even possible? (No keyway or other locating method?)

So what's being said is, the AoA vane hub is rotated in error by one screw-hole place?

For it to be able to be so misaligned seems impossible - for the main casting to not be designed D shaped, or have a flat edge would be deeply worrying. But it is a compelling scenario since the output error is so consistent.

I'd personally discounted damage to the vane after the second crash, and would be mystified if it were to be a mechanical problem since the vanes are so strong. They look frail, but they're anything but.
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I think that it's been established elsewhere on the thread/s that there are lugs or something that means that they can only be installed in the correct orientation - but tdracer has said that he has seen them carefully machined off so that they can in fact be incorrectly fitted...

The only reason I can think of for doing that would be for one unit to be able to fit a new aircraft. Hmmm . . . now let me think.

'We could make those NG vanes fit the MAX if we shaved the lug a little.'

Since it has not been disclosed the conditions and settings where the engine nacelles provide extra lift and nose up the ac (if/when MCAS kicks in)...an AoA sensor is meaningless.

The UT AoA sensors have an offset bolt pattern to insure correct installation.

https://cimg0.ibsrv.net/gimg/pprune....945e7fa95e.jpg

Operational useof angle of attack - boeing
 

Does this help

OPERATIONAL USEOF ANGLE OF ATTACK

A nuance that I have not seen stated here previously, one well worth considering as people go back and forth arguing over whether or not the pilots should have saved the day:

MCAS introduced a single point of failure that without pilot intervention in a highly specific way results 100 percent of the time in the aircraft flying itself into the ground. Either the pilot nails the answer to the question while all hell is breaking loose and g-loads are all over the place (about a system which they had no awareness existed), and they do it within a very very short period of time, or the airplane will 100 percent fly itself into the ground. Straight into the ground BTW.

I cannot recall any other instance of a single point of failure system or sensor (or any system for that matter) on a commercial airplane which places the airplane in a state where the only chance for survival is a single action by the pilot, without which the airplane will crash. Once the AOA failed in Indonesia the airplane was essentially trying to fly itself into the ground. The Capt. kept that from happening for a bit, then it succeeded when he handed the airplane to the FO to grab the book and look for an answer that was not in fact there.

I can recall tons of technical issues that resulted in incidents and accidents, in fact I’ve survived a few on my own, but none where the failure of a single sensor meant that a perfectly good airplane was literally trying to kill everyone on board.

We can go round and round about whether or not the flight crew should have been able to aviate their way out of the circumstance they found themselves in, but if the penalty for failure to act quickly enough and perfectly enough on any given in-flight issue on a single sensor and a system about which you knew nothing was immediate death for you and your passengers would you still choose to fly?? Are you that certain of your perfection in the air??

If you knew that there might be a system on your airplane that you knew nothing about and that had the power to command the airplane to try to kill you, would you fly in that airplane, or god forbid take command of it with a couple hundred people in your care??

That is exactly what Boeing did to every MAX crew that flew the airplane. And whether with ill-intent or not they did it knowingly and deliberately. We don’t know them now, but Boeing is filled with smart people. Someone(s) knew exactly what Boeing was doing putting MCAS into service in the clandestine way they did, and I presume it was done that way for an (as yet unknown) reason. Those people will speak up at some point, or I hope they will anyway because it was no accident that MCAS anonymously arrived in the MAX without flight crews being made aware of its presence.

We can argue that the Lion Air crews who successfully survived an otherwise fatal experience should have alerted the airline, and we can argue a ton of other things too.

What we cannot argue, for one moment, is that the regulatory system that allowed Boeing to self-certify safety of the 737 MAX functioned as intended.

What we cannot argue is that Boeing and the regulatory system produced a safe airplane.

Quite to the contrary they produced an airplane that with the right type of single sensor failure would immediately try to kill everyone on board, with only the immediate and correct intervention of the pilots, who had no idea that the system trying to kill them even existed, to prevent that outcome.

The surprising thing isn’t that it happened, it’s that it took so long to happen.

Regards-
dce

Here is your link: OPERATIONAL USE OF ANGLE OF ATTACK (pdf)

What about positioning of the internal sensors? Are they indexed for location?
Can you take the units apart?