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Ethiopian Airlines 737 MAX Investigation Preliminary Report

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Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#131

Post by cjbprime »

3JPLW wrote: post #94
kayfox wrote: post #88

Earlier quoted context omitted.

> It's possible that aerodynamic load (of the stabilizer opposing the elevator) made it physically impossible to manually trim given any mistrim at the time the cutout happened, given the airspeed they had. Its been noted in previous discussions that while it would be difficult, the load can be overcome if both pilots were to operate the manual trim wheel at the same time. Not that its a good situation to be in.

Is it still possible at or near VMO? And when the trim is maxed out? I don't think I've seen an authoritative answer on that, and that's the situation they faced.

Another commenter pointed out that the captain is pulling back as hard as he possibly can on the yoke; releasing it to turn a trim wheel instead may have been just as deadly.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#132

Post by msbarnett »

cjbprime wrote: post #125
msbarnett wrote: post #115

Earlier quoted context omitted.

My (non-expert) reading is that the co-pilot couldn't move the wheel, while the pilot was engaged in fighting to to keep the stick pulled back (a Swedish pilot tried this scenario in a simulator last week and literally had to keep both arms locked around the stick towards the end). Counter-intuitively, letting go of the stick in brief increments might have been the correct move. Letting the nose pitch down would take…

> they were only 7,000 feet above the ground No, it's worse: the origin airport is at 7000ft elevation. They only had around 1000ft height AGL for all of the flight. So I agree that releasing the elevator at all seems surely suicidal.

They're at 12,000-14,000 feet altitude at 05:43ish, when the co-pilot reports the non-functional manual trim. So ~6,000-7,000 height.

Still damn close to the ground to be comfortable letting the plane dive.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#133

Post by caconym_ »

cjbprime wrote: post #104
wereHamster wrote: post #11

Earlier quoted context omitted.

> Aerodynamic loading prevented manual trimming using the trim wheels. Are the trim wheels mechanically connected to the trim mechanism in the back? Is there no way to trim the horizontal stabilizer electrically without also enabling MCAS? What would happen if the pilots continually pressed the trim up switch on the yoke? That should've prevented MCAS from activating, right? I thought Boeing airplanes were built such…

> Is there no way to trim the horizontal stabilizer electrically without also enabling MCAS? Correct. One wonders if this is a consequence of trying to maintain the type rating and therefore not being able to introduce any pilot training about the MCAS feature, and therefore not being able to introduce any control features for it.

Good question. This is what makes these accidents so bad in my eyes: they weren't caused by a defect or flaw in the traditional sense, but rather by a system that seems to have been conceived solely to allow Boeing to skirt retraining/recertification requirements, to sell more planes.

Such a system should have been subject to extreme scrutiny, and honestly it beggars belief that the potential for these accidents wasn't seen. "This system can trim the nose down beyond the authority of the manual controls, based on readings from a single non-redundant sensor" should have been more than enough to get the gears turning, and it seems that the deeper one looks it only gets worse.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#134

Post by pdonis »

linuxftw wrote: post #46
dao- wrote: post #31

I'm starting to think that disabling MCAS isn't even a sane option because then the pilots are exposed to unexpected aerodynamic characteristics due to the plane's weird design. Does this make sense?

Many people have this opinion. You can't both require MCAS and be okay with disabling it at the most critical portion of a flight where the system is needed most.

> You can't both require MCAS and be okay with disabling it at the most critical portion of a flight where the system is needed most.

If MCAS activates when it isn't supposed to, which is what happened here, disabling it is what you want to do--to stop it from doing an incorrect thing. The plane was not in a situation where MCAS was needed; it was perfectly flyable without MCAS in the flight regime it was in.

The problem is that, if you disable MCAS (which requires disabling the entire electric stability trim system) without first using the electric trim system to get back to something close to neutral trim, you will be stuck with a lot of nose down trim that you can't remove fast enough with the manual trim wheel. It looks like that's the situation this flight got into.

But if you first use the electrim trim system to get back to something close to neutral trim, and then, before MCAS has a change to mess it up again, disable the entire electric stability trim system, you're ok. How do we know? Because that's what the first Lion Air flight (the one the day before the one the crashed) did, because an off duty pilot that was riding in the jump seat figured out what was happening and how to deal with it and told the pilots what to do.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#135

Post by ominous_prime »

js2 wrote: post #122
davepage wrote: post #43

Earlier quoted context omitted.

It does not appear to be "precisely" the procedure, in that sufficient nose up trim was not selected by the yoke manual trim switch prior to pulling the trim cutouts. And then they did not work the mechanical trim wheel hard enough to reset the residual nose down trim. And, the crew left the power setting at climb throughout almost the entire sequence, so they oversped the airframe. And, when they (against procedure)…

You can still point back to Boeing for not recommending flight simulator training of this failure scenario. One thing that I've wondered though as I've read more about MCAS. MCAS can't kick in till the flaps are fully retracted. Usually when something goes wrong in response to an action, the response is to undo the action. Why isn't the procedure or even the pilot instinct to re-extend the flaps when the nose down oc…

I would guess that the node down attitude quickly put them over VFE, so even it they could extend the flaps (I don't know if the flight system would prevent that or not) they would at least second guess doing so and continue other avenues of troubleshooting.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#136

Post by sidlls »

holler wrote: post #74
fgonzag wrote: post #62

Earlier quoted context omitted.

At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1…

this may be a naive question but with all of the advanced technology on these planes, why isn't there a check for altitude before any automated command runs which says "hey we just took off, are 400ft above ground, MCAS is saying nose down, we will crash if that command runs, CANCEL"

It's not that simple. If the AoA is too high that can cause a stall and crash, too.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#137

Post by cjbprime »

holler wrote: post #74
fgonzag wrote: post #62

Earlier quoted context omitted.

At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1…

this may be a naive question but with all of the advanced technology on these planes, why isn't there a check for altitude before any automated command runs which says "hey we just took off, are 400ft above ground, MCAS is saying nose down, we will crash if that command runs, CANCEL"

You'll 100% for sure crash if you stall at 400ft above ground. MCAS is designed to prevent stalls.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#138

Post by javagram »

holler wrote: post #74
fgonzag wrote: post #62

Earlier quoted context omitted.

At 05:43:20, approximately five seconds after the last manual electric trim input, an AND automatic trim command occurred and the stabilizer moved in the AND direction from 2.3 to 1.0 unit in approximately 5 seconds. The aircraft began pitching nose down. Additional simultaneous aft column force was applied, but the nose down pitch continues, eventually reaching 40° nose down. The stabilizer position varied between 1…

this may be a naive question but with all of the advanced technology on these planes, why isn't there a check for altitude before any automated command runs which says "hey we just took off, are 400ft above ground, MCAS is saying nose down, we will crash if that command runs, CANCEL"

MCAS system is supposed to stop the plane from stalling.

The faulty AoA sensor is causing the plane to think it’s about to stall and therefore MCAS works as designed to prevent the pilot from putting the plane into a stall.

Of course the design is wrong because the plane is actually pointing toward the ground and MCAS thinks it’s pointing to the sky...

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#139

Post by linuxftw »

pdonis wrote: post #134
linuxftw wrote: post #46

Earlier quoted context omitted.

Many people have this opinion. You can't both require MCAS and be okay with disabling it at the most critical portion of a flight where the system is needed most.

> You can't both require MCAS and be okay with disabling it at the most critical portion of a flight where the system is needed most. If MCAS activates when it isn't supposed to, which is what happened here, disabling it is what you want to do--to stop it from doing an incorrect thing. The plane was not in a situation where MCAS was needed; it was perfectly flyable without MCAS in the flight regime it was in. The pro…

> The plane was not in a situation where MCAS was needed;

As far as I can tell, there is no takeoff (pitch up) situation where MCAS is not needed on the MAX 800. It's required for safe operation of the plane, otherwise the nose might pitch up unexpectedly into a stall.

As I said, the system can't both "be required for safe operation of the plane" and "it's safe to disable MCAS while it's malfunctioning during takeoff." You have to pick one.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#140

Post by ummonk »

rdiddly wrote: post #119

Reading through the chronology in section 1.1, it feels like a movie where the aircraft is a malevolent entity that's trying to kill them. So if I were in the cockpit I'm sure it would've been some mix of fear and anger. My life's not in danger though, so I'm only left with the anger, on their behalf, knowing some greedy bunch of assholes were effectively that malevolent entity, whose will was expressed via the aircr…

Why is that getting downvoted? What the heck.
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