Ethiopian Crash

Hangar Flying
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I think the transcript is pretty accurate, these are all the involved parties in the investigation:

ECAA and Ethiopian Airlines Group -Technical Advisor to AIB
NTSB - Accredited RepresentativeState of Design and Manufacturer
BEA - Accredited representative,State which provided facilities & experts fort he read out of DFDR & CVR
EASA-Technical Advisor to AIB

And the accompanying information on how the Stab Trim works:

Stabilizer Trim Stabilizer trim switches on each control wheel actuate the electric trim motor through the main electric stabilizer trim circuit when the aircraft is flown manually. With the autopilot engaged, stabilizer trim is accomplished through the autopilot stabilizer trim circuit. The main electric and autopilot stabilizer trim have two speed modes: high speed with flaps extended and low speed with flaps retracted. If the autopilot is engaged, actuating either pair of stabilizer trim switches automatically disengages the autopilot. The stabilizer trim wheels rotate whenever electric stabilizer trim is actuated.The STAB TRIM PRI cutout switch and the STAB TRIM B/U cutout switch are located on the control stand. If either switch is positioned to CUTOUT, both the autopilot and main electric trim inputs are disconnected from the stabilizer trim motor.Control column actuated stabilizer trim cut out switches stop operation of the main electric and autopilot trim when the control column movement opposes trim direction. When the STAB TRIM override switch is positioned to OVRD, electric trim can be used regardless of control column position.

the way I read it is that they remove the electrical power to the controls and to the autopilot commands(from the AP to the motor) but don’t actually shut down the electrical trim motor. Besides, does MCAS not operate outside of the AP’s regime given that it’s conceptually always functional?

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I only know what is in my 2800 pg 737 manual and it goes no deeper than what you’ve posted. I would have assumed that MCAS used the AP trim motor. Therefore flipping the cuttout swithches should remove power from them motor regardless of what MCAS may have had in mind. If MCAS is a 3rd motor then that would be a very big deal. Well
an even BIGGER deal. Who knows? I am officially way out of my league. I guess we will all learn together when Boeing finally posts their fix.

I see that I really didn’t respond to your logical question. Answer: I don’t know. I was taught that the switches removed electrical power and rendered the motors useless except maybe as brakes to prevent feathering in the airflow. Additionally, I know longer trust what I was taught.

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The way I read it is that you don’t actually remove power from the motor, you remove it from the control inputs in highly specific positions. To me the motor still has electrical power available, though I might be reading it in a different way.

I technically would say that they would be useless yes, though if you add in a third system that has it owns independent way to operate the motors that is not reliant on the AP or pilots trim inputs


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Here’s what I read


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OK I get it now. I will resist the desire to edit some if the stupid “stream of consciousness” dribble I wrote above. The cutouts worked. But those poor pilots were now left with nothing but manual trim and a stab that was dialed very nose low. I have used the manual trim wheel at all normal speeds below Vne/Mmo and it is moveable. But it is also very slow. To move it more quickly there is a handle that can be unstowed and turned like a grinder. Speed certainly does make a difference though. The faster the speed, the more up-force on the stab. Of course there is also more down-force available to the elevator. But as we’ve discussed a-plenty in this thread, the stab is much bigger. So it wins every time. And anyway, with one pilot pulling full aft on the yoke that may create such forces on the stab that even with the handle, at that speed, the strength required to turn it quickly enough to stop the descent would be a challenge for anyone.

Anyway, I am sorry for the “deeper hole” comment above. Honestly though, I think I would have used power too. Those underslung engines create a huge amount of pitch moment. That may have seemed like the only hope. To my fellow airline pilots who answered my defense of both crews by saying, “why didn’t they just use the cutouts!” (which I have to add was often couched in a bit of West-vs-everbody-else arrogance)—well, they can suck it!

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106

Yeah, the poor guys were set up to fail.
That’s what it looks like to me, anyway.

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So here is a question for Boeing:

If you do the right thing and remove MCAS entirely, how do you explain to grieving families why it was there to begin with? Or, if you promise a fix through changing a few lines of code, how can anyone trust your jet?

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108

Hear hear, it’s an annoying kind of arrogance, as if only pilots in the west know how to fly


Tell me about it, I was questioning what I know about Boeing jets today at work. Not really a healthy line of thinking if you get my drift?

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Some marketing drivel from Boeing:

I have a hard time believing any of those words these days.

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Wow. If I was feeling cynical, that would seem like a lot of corporate word salad to reassure the shareholders. There was a lot of ‘we are great’ and absolutely no ‘we did that wrong’ in there.

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Not quite the “we own this” from a few days ago but its not horrible. The most offensive part is to characterize the system as a link in the chain. There was no chain. There was only MCAS. Everything else was just along for the ride.

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Here’s a reddit post about it:

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Yeah, I got almost 5 minutes into that thread before the shouty-ness overwhelmed me. I really have no patience for that level of self importance. I think I’m getting old! :triumph:

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We all are! But the Vox video posted above is actually excellent–just ignore the reddit bs. And, again, thank the gods for the responsible journalism that has explained this disaster when officialdom only offered silence.

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Same here.

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That Vox video is pretty good, saw it being slandered on Reddit quite a bit but eeh, the Boeing sub is a bit biased most of the time.

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Wow. VOX actually didn’t blame POTUS but provided good journalism.

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120

Interesting article, from a coder


Neither such coders nor their managers are as in touch with the particular culture and mores of the aviation world as much as the people who are down on the factory floor, riveting wings on, designing control yokes, and fitting landing gears. Those people have decades of institutional memory about what has worked in the past and what has not worked. Software people do not.

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121

I’ll say it again: In the 737 Max, the engine nacelles themselves can, at high angles of attack, work as a wing and produce lift. And the lift they produce is well ahead of the wing’s center of lift, meaning the nacelles will cause the 737 Max at a high angle of attack to go to a higher angle of attack. This is aerodynamic malpractice of the worst kind.

I’ve only made it about halfway through. And I largely agree. But this paragraph is one I take issue with. ALL 737s have large pitch forces with large power changes. I didn’t fly the Max9 but ALL my friends who have say that the flight characteristics matched exactly those of the -900ER. And that feedback is without MCAS or other “hacks” besides “Speed Trim”. The author really doesn’t KNOW for certain the extent of the negative qualities that the new designed forced on the aerodynamics of the Max. He has a hunch, maybe a good one. But a hunch is not a case for “aerodynamic malpractice”.

I am not reversing myself vice what I have written earlier. I too am certain of serious malpractice, malfeasance, malevolence, mal-something. I just don’t have any idea if it extends to the nuts-n-bolts aerodynamic design of the machine.

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