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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

#91

Post by msbarnett »

treis wrote: post #61
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…

>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.

Looks like you're right.

But apparently the option 2 maneuver (relax pressure on stick, then crank) hasn't been covered in a Boeing 737 manual since the 200 series in the 1980s.

So even given the extra room, there was no documentation covering that possible recovery scenario.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#93

Post by kayfox »

fgonzag wrote: post #13
dsfyu404ed wrote: post #6

Earlier quoted context omitted.

Per the article a combination of things put them in that situation. Not just MCAS. Why is everyone so wedded to the narrative that this is the fault of MCAS and nothing else? Complex systems that have millions of man hours spent making them safer don't usually have back to back failures because of one faulty subsystem. We've incrementally refined commercial air travel to the point where single source accidents are ba…

It's true there were aggravating factors, like the inability to manually rectify trim, which (would seem to me) would be a aerodynamic or design issue. The point still stands, the root cause was MCAS, without it this would never have happened. MCAS would not have pitched them into a dive, and even if they were pitched into a dive by some non MCAS system, they would have been able to turn on electric trim and recover.…

> It's true there were aggravating factors, like the inability to manually rectify trim, which (would seem to me) would be a aerodynamic or design issue.

I don't see in the report that the pilots attempted to both operate the manual trim wheel at the same time. I'm not sure if its explicit in the training, but in the manual its made clear that pilots may need to work together to move the trim out of extreme positions when the electric system is not available, and that doing so will not break the manual trim system.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#94

Post by 3JPLW »

kayfox wrote: post #88
cjbprime wrote: post #71

Earlier quoted context omitted.

> 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 el…

> 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.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#95

Post by cjbprime »

kayfox wrote: post #88
cjbprime wrote: post #71

Earlier quoted context omitted.

> 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 el…

> 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.

> 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.

I haven't seen that noted anywhere, and have seen it theorized as impossible without motor assist, given their airspeed and with the elevator opposing. Got a link?

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#96

Post by daddylonglegs »

Rooster61 wrote: post #21
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…

> They must cut it at a moment where the stabilizer isn't grossly mistrimmed with respect to level flight, OR they may well need to re-engage it and race the MCAS to get into a close-to-proper trim setup prior to cutting out the stabtrim and assuming manual trim control. All while keeping the plane in the air, reading the manual, and attempting not to lose composure knowing that the same thing has happened to another…

> > They must cut it at a moment where the stabilizer isn't grossly mistrimmed with respect to level flight, OR they may well need to re-engage it and race the MCAS to get into a close-to-proper trim setup prior to cutting out the stabtrim and assuming manual trim control.

> All while keeping the plane in the air, reading the manual, and attempting not to lose composure knowing that the same thing has happened to another flight that lost all hands.

Additionally an angle of attack (AOA) sensor failure also triggers an unreliable airspeed warning so the pilots no longer trust their airspeed sensors or their AOA sensors while trying to judge pitch and speed. If they go too fast the control forces overpower them, if they go too slow they are more likely to stall.

I don't think Boeing gamed out or tested in a simulator the human factors involved in an AOA failure at takeoff, particularly for pilots who - like the Lion Air pilots - are entirely ignorant of MCASes existence.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#97

Post by kayfox »

ams6110 wrote: post #51
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…

Yes, pilots selecting "up" on the trim switch should stop and override MCAS. But it also "resets" MCAS so that it will pitch down again on its next cycle. So you'd have to be constantly correcting it, or switch the electric trim off entirely (i.e. treat it as runaway trim).

Or toggle the trim control switch when MCAS starts up again.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#99

Post by snuxoll »

Rooster61 wrote: post #21
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…

> They must cut it at a moment where the stabilizer isn't grossly mistrimmed with respect to level flight, OR they may well need to re-engage it and race the MCAS to get into a close-to-proper trim setup prior to cutting out the stabtrim and assuming manual trim control. All while keeping the plane in the air, reading the manual, and attempting not to lose composure knowing that the same thing has happened to another…

> reading the manual

Runaway stabilizer is a memory item, there should be no reading of the manual involved.

Unfortunately the design of MCAS defeated the checklist of this particular memory item when in lower flight altitudes - which goes back to the argument that the 737 MAX never should have been given the same type rating as the older models.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#100

Post by mpweiher »

AnabeeKnox wrote: post #87
smaili wrote: post #24

Earlier quoted context omitted.

Just out of curiosity, will there actually be any punishments handed out beyond just a slap on the wrist? Or is Boeing far too large of a corp to take on?

This is an absurd comment. The rule of law works in the USA as much as it does in other developed countries. There is no such thing as "too large to take on". I note though that there is not yet any evidence of a crime having been committed.

> There is no such thing as "too large to take on"

Let me get you up to date:

"The deal — four years after the 2008 collapse of Lehman Brothers nearly brought down the financial system — was criticized at the time, raising concerns about whether some banks had grown too big to face criminal indictment."

"Citing anonymous officials close to the case, the New York Times reports that federal prosecutors spent months debating whether to issue criminal indictments for money laundering. Authorities eventually ruled it out as such charges could ultimately cost HSBC its charter to operate in the US, seriously undermining the country’s fragile economic recovery."

https://www.nytimes.com/2017/12/11/business/dealbook/hsbc-us...

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