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Ethiopian Airlines 737 MAX Investigation Preliminary Report

ecaa.gov.et

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Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#71

Post by cjbprime »

davepage wrote: post #43
Rooster61 wrote: post #7

> The crew performed runaway stabilizer checklist and put the stab trim cutout switch to cutout position and confirmed that the manual trim operation was not working. This is very damning to Boeing. It's precisely the procedure they prescribed and intended to mitigate possible MCAS caused trim runaway. In light of the fact that they put this in place as a justification for moving the engines forward without reclassif…

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)…

> sufficient nose up trim was not selected by the yoke manual trim switch prior to pulling the trim cutouts

The EAD/service bulletin doesn't talk about sufficient nose up trim or caution against performing the cutout with even a slight mistrim.

> And then they did not work the mechanical trim wheel hard enough to reset the residual nose down trim.

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. And, the captain is pulling back on the yoke as hard as he can, so he's unavailable to let go of it and grab a trim wheel instead without immediately losing altitude.

> And, when they (against procedure) (apparently) turned the electric trim system back on

It seems sensible to assume -- and the report states -- that they did this because they found that manual trim was impossible in these circumstances.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#72

Post by treis »

salex89 wrote: post #4

This isn't only MCAS issue anymore... If there are issues with manually rectifying trim after it went haywire because of any reason, that might be a problem. Interesting to find out was that an issue with older 737 models, just without severe runaway trim events.

I think people are reading too much into an ambiguous statement. It says:

>At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working.

"Manually" here could mean manual electric control. 8 seconds seems an awfully short time for the Captain to ask if trim is functional, FO to say no and ask to try manual, Captain to say Yes, and for the FO to try the wheel and conclude it's not working.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#73

Post by JRKrause »

fgonzag wrote: post #62
weaksauce wrote: post #53

Earlier quoted context omitted.

Thechnically they could have used the thumb switch and regained level flight to override the mcas system temporarily and then shut off the electrical system to the stab and trim manually thereafter. However, they didn’t know about the mcas system and the troubleshooting steps that Boeing has for that mode of failure were insufficient for this precise scenario.

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…

The manual electric trim inputs override the MCAS inputs[0], so they could have kept applying the appropriate trim regardless of the MCAS malfunction.

[0] Appendix 1, 05:40:30 (You can see the AND command being canceled by the pilots manual electric ANU command)

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#74

Post by holler »

fgonzag wrote: post #62
weaksauce wrote: post #53

Earlier quoted context omitted.

Thechnically they could have used the thumb switch and regained level flight to override the mcas system temporarily and then shut off the electrical system to the stab and trim manually thereafter. However, they didn’t know about the mcas system and the troubleshooting steps that Boeing has for that mode of failure were insufficient for this precise scenario.

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"

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#75

Post by msbarnett »

davepage wrote: post #43
Rooster61 wrote: post #7

> The crew performed runaway stabilizer checklist and put the stab trim cutout switch to cutout position and confirmed that the manual trim operation was not working. This is very damning to Boeing. It's precisely the procedure they prescribed and intended to mitigate possible MCAS caused trim runaway. In light of the fact that they put this in place as a justification for moving the engines forward without reclassif…

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)…

> And, the crew left the power setting at climb throughout almost the entire sequence, so they oversped the airframe.

I believe that's correct given that they had an Unreliable Airspeed Indicator warning (due to the malfunctioning AoA sensor), per the memory items on the UAI checklist.

It makes the forces on the trim wheel much worse, which explains why they couldn't turn it, but it's the correct checklist response to the conditions observed, and the Boeing/FAA directive completely failed to take the impact of this response into account.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#76

Post by Rooster61 »

fgonzag wrote: post #59
usrusr wrote: post #44

Earlier quoted context omitted.

Being capable of performing a glide without electricity does not necessarily imply that a no-power glide can safely be entered from extreme conditions like diving too fast with trim set to insane.

But being able to actually utilize all your control surfaces without electrical power must be a basic requirement. They could make the trim control wheel mechanically assisted, for example (since there are cases where electronic trim control is required because because of the amount of force needed to turn the wheel)

> They could make the trim control wheel mechanically assisted

I'd imagine it already IS mechanically assisted. There is a limit to how much you can amplify a pilot's input mechanically, and I'd imagine the load on the aircraft exceeded the amount of amplification needed.

I.e. your car has power steering, so the car manually adds power to the turn based on the user's input. That doesn't mean that something in the road can't override the input of both the driver and power steering and jerk the wheel.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#77

Post by [deleted] »

davepage wrote: post #43
Rooster61 wrote: post #7

> The crew performed runaway stabilizer checklist and put the stab trim cutout switch to cutout position and confirmed that the manual trim operation was not working. This is very damning to Boeing. It's precisely the procedure they prescribed and intended to mitigate possible MCAS caused trim runaway. In light of the fact that they put this in place as a justification for moving the engines forward without reclassif…

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)…

[deleted]

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#78

Post by dsfyu404ed »

Rooster61 wrote: post #70
dsfyu404ed wrote: post #66

Earlier quoted context omitted.

If the pilot, who hopefully has thicker skin than people on the internet, moves the buttons and levers properly MCAS should never have to do anything. It's only supposed to actually do anything when you let the nose pitch up a little too much (which the system will detect using the AoA sensors)[0]. It's like automatic braking in a new car, if you drive the way you're "expected to" you shouldn't be activating it often…

Again, please post a source backing this claim up. And it would be appreciated if the folks that died commanding this flight were not referred to as "meat bags".

Edited the original.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#79

Post by Gibbon1 »

fgonzag wrote: post #52
msbarnett wrote: post #10

Earlier quoted context omitted.

> If there are issues with manually rectifying trim after it went haywire because of any reason, that might be a problem. It's not so much a "problem" as it is "physics". If the stabilizers are forcing the nose down, and the pilot pulls back on the stick (engaging the elevators) to pull the nose up, the forces exerted on the stabilizer are such that, in extreme cases, human force is insufficient to move the manual wh…

Layman question here: Are there real scenarios where you want to have both control surfaces opposing each other so heavily? Are there real cases for having the trim trying to pitch the plane down while the pilot is trying to pitch up with the stabilizer? Or should we limit the trim so it never actually opposes the pilots intentions? (Maybe set it to a neutral position and disengage auto function if this condition is…

I think the issue is the difference between the force needed to trim the aircraft and the acceptable control gain between the yoke and the elevator. I think with light aircraft trim is what you think of it. Slightly centers the yoke so the aircraft will fly level without control input.

I think what's going on with the 737-MAX is the needed trim is way beyond what's needed to fly the plane.

I'm now wondering is the MACS is needed because the tendency to pitch up also exceeds the pilots control inputs which is why it had to be on the elevator and have that much authority. Meaning once the aircraft pitches up the pilot doesn't have enough authority to push the nose back down.

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