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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

#61

Post by treis »

msbarnett wrote: post #10
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.

> 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…

>less great at a height of 1,000 feet.

Am I reading the chart on page 27 wrong? Because it looks like they reached a maximum height of 7,000 feet. Also looks like they were continuing to slowly climb until they re-enabled electric trim.

EDIT TO ADD:

Page 12 also says:

>about 32 seconds before the end of the recording, at approximately 13,400 ft

Which is a bit under 6,000 feet higher than the airport.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#62

Post by fgonzag »

weaksauce wrote: post #53
fgonzag wrote: post #36

Earlier quoted context omitted.

This means that Boeing is now 100% liable for the crash, as there was nothing the airline could've done in this scenario. It also means that the aircraft will have to be re-designed and re-classified before it ever flies again (it's now a very clear design error, not a training or communication error)

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 1.1 and 0.8 units for the remainder of the recording.

It seems they tried it but MCAS kicked 5 seconds after they turned on the electrical trim. They didn't have enough time to correct the stabilizer. I don't know how fast returning a stabilizer to neutral position can be done, but they probably thought they had more than 5 seconds. They were probably going to turn off electronic trim control afterwards.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#63

Post by proctor »

wereHamster wrote: post #11
mhandley wrote: post #3

Indeed looks like they did disable MCAS using the stabilizer trim cutout switches, but the aircraft was trimmed nose down when they did so. Aerodynamic loading prevented manual trimming using the trim wheels. They eventually turned electric trim back on, as they didn't really have any other options, but didn't trim back enough, and left it turned on. At this point the right airspeed indicator (which should be more re…

> 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…

this video[0] from "mentour pilot" on youtube explains the stabilizer system quite well.

it seems the trim wheels are connected manually to the trim mechanism in the back, but when the trim stabilizers are in an extreme position the wind loading on them makes it very hard/impossible to rotate the trim wheels manually.

from what i understand, one way to relieve/lessen the wind loading so that the manual wheels can be used again is to (in the case of trim down) dive the plane. this would lessen the wind loading on the stabilizer and allow the manual wheels to move again. but you would need "room" to dive, something they did not have in this case.

[0]https://www.youtube.com/watch?v=xixM_cwSLcQ

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#64

Post by Rooster61 »

sctb wrote: post #57
dmix wrote: post #56

Earlier quoted context omitted.

How is that the same? The BBC article doesn't contain even 20% of the information as the full report (including multiple charts).

You're absolutely right, it's not the same (in this sense “duplicate” is a misnomer—or at least should be applied to the thread or topic and not the submitted link).

If that's the case, it would be appreciated if this was moved back, or at least re-posted. It appears worthy of being visible based on the amount of discussion it generated in a short time. Moving it to this thread effectively threw a bucket on the fire.

This document is a big deal.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#65

Post by sctb »

Rooster61 wrote: post #64
sctb wrote: post #57

Earlier quoted context omitted.

You're absolutely right, it's not the same (in this sense “duplicate” is a misnomer—or at least should be applied to the thread or topic and not the submitted link).

If that's the case, it would be appreciated if this was moved back, or at least re-posted. It appears worthy of being visible based on the amount of discussion it generated in a short time. Moving it to this thread effectively threw a bucket on the fire. This document is a big deal.

OK! We've put it back.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#66

Post by dsfyu404ed »

Rooster61 wrote: post #60
dsfyu404ed wrote: post #35

Earlier quoted context omitted.

The MAX is stable in normal flight. It's only when you are pitched up does the engine placement make it want to pitch up even more (and it is only a problem at a speed that is low enough that the normal stabilizer control doesn't have enough control authority to push it back) hence MCAS forcing the nose down every so often via the trim. A normal flight does include pitching up but it does not include pitching up at s…

> MCAS is specifically designed for an edge case Source? That's the first I've heard that it's only for edge cases.

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.

[0] https://theaircurrent.com/aviation-safety/what-is-the-boeing...

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#67

Post by cjbprime »

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…

I've read that it takes the trim motor 30 seconds to move the jackscrew completely along its path. It was found all the way at one end in the wreck. So naively, it takes up to 15 seconds of continuous motor operation to recover level flight.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#68

Post by Rooster61 »

sctb wrote: post #65
Rooster61 wrote: post #64

Earlier quoted context omitted.

If that's the case, it would be appreciated if this was moved back, or at least re-posted. It appears worthy of being visible based on the amount of discussion it generated in a short time. Moving it to this thread effectively threw a bucket on the fire. This document is a big deal.

OK! We've put it back.

Err...Not quite, its still under the poster of the bbc article, but the effort is appreciated nonetheless. You guys rock. :)

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#69

Post by jordache »

>The left Indicated Airspeed increased, eventually reaching approximately 458 kts and the right Indicated Airspeed reached 500 kts at the end of the recording. The last recorded pressure altitude was 5,419 ft on the left and 8,399 ft on the right.

How can the sensors record such different readings?

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#70

Post by Rooster61 »

dsfyu404ed wrote: post #66
Rooster61 wrote: post #60

Earlier quoted context omitted.

> MCAS is specifically designed for an edge case Source? That's the first I've heard that it's only for edge cases.

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".
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