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Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

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Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#51

Post by DougBTX »

tyingq wrote: post #38
userbinator wrote: post #33

Earlier quoted context omitted.

It does... http://www.b737.org.uk/images/throttlequadrant.jpg See the scale with "APL NOSE UP" and "APL NOSE DOWN" next to the trim wheels. Whether the pilots noticed it (or the attitude indicator pointing nose-down, or the rapidly decreasing altimeter...) is the question.

Ah, so that indicator would have been abnormally in the "nose down" area after MCAS over adjusted it. Interesting. Information overload, and nobody looked because that amount of auto adjustment wasn't anticipated. And also means they didn't correlate the fairly noisy/visual turning off the wheels to get it in that position.

There was a PDF incident report going around earlier with a chart showing a graph of the inputs from MCAS and the pilots over a period of time. There was a "nose down" command from MCAS, followed by a "nose up" command from the pilot, then a "nose down" command from MCAS, a "nose up" command from the pilot... repeated about 20 times in a row...

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#52

Post by ams6110 »

CaptainZapp wrote: post #41
ams6110 wrote: post #40

Earlier quoted context omitted.

So any time there's a crash now, we're going to ground the worldwide fleet of that model of aircraft until we have a final report on the cause?

If it happens to a brand new plane? I'd say: Yes; that's reasonable. At least until the cause is known. Edit : Some clarification

Cause is always complicated in an air crash. We don't officially know the cause of either of these crashes.

When MCAS was established to be a likely factor in the first crash, Boeing issued an emergency airworthiness directive to all operators of the 737 Max, alerting pilots to the possibility of undesired nose down trim, and reminding them that the runaway trim procedure would disable it.

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#53

Post by acqq »

bredren wrote: post #43
yg6ht5 wrote: post #39

Earlier quoted context omitted.

$1M sounds like pocket change after all that has happened.

Market cap loss since crash of flight 303 is $27 billion. https://ycharts.com/companies/BA/market_cap

Which is still nothing compared to the increase in Boeing’s market cap since some three years ago.

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#54

Post by karlkatzke »

dba7dba wrote: post #23
sokoloff wrote: post #20

Earlier quoted context omitted.

40 seconds is an eternity to accomplish the memory items on runaway stab trim non-normal checklist. It’s literally “control column - hold firmly” (already a given, since MCAS only affects manual flight and the increased back pressure required is the cue that something is amiss), “autopilot and autothrottle - disengage” (click-click, click-click), (if runaway continues) “stab trim cutout switches - cutout (both)”, (if…

Main stream media made it sound like 40 seconds is way too short of a time to troubleshoot the issue. But now that you state it that way, I gotta agree with you it's not Only Boeings fault. Sure they are big significant part of the issue. But not the only part.

As someone who's done a bunch of human factors design training for critical situations in a previous career as a UI/UX designer and now works as a systems engineer doing a bunch of alerting, 40 seconds is too short of a time to troubleshoot the issue.

When this situation happens, five things happen at once. MASTER CAUTION (whoop, whoop noises and a big red light!), ALT DISAGREE alert on the MFD, Incorrect Airspeed on the MFD, the stick shaker goes off, and by the way, if you take the time to look down at the throttle section of the dashboard with all those other alerts going off, you'd see that there is suddenly a lot of trim on the APL trim indicator but the trim wheel doesn't actually move (which would provide an audible 'click click click' that would probably trigger that there was a problem with trim.

Each of those things has a separate memory checklist that you have to run down, and subtract ten seconds to register them, prioritize, communicate with the other pilot, and start executing them.

The worst part here is that they've added another alert and then changed how the airplane will fly in the middle of an emergency. While the extra alert narrows down the number of branches from the "prioritization" part of the checklist, I'm not sure that's "fixing" the problem.

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#55

Post by in_cahoots »

tapland wrote: post #11
VBprogrammer wrote: post #2

That's not very surprising to anyone who has been following along. The more interesting question is why they failed to identify the trim runaway condition, or if they did indeed identify it, why the procedure failed to correct it? This is significantly different to the Lion air incident where you can easily give the pilots the benefit of the doubt because the failure mode hadn't been previously identified. The detail…

Maybe time was an issue? Saw in an earlier post that the issue had to be mitigated within 40 seconds of it occurring.

That 40 second quote is a bit misleading. As I understand it, if the pilots do absolutely nothing then they only have 40 seconds until MCAS has adjusted the trim the maximum amount. But the Lion Air flight flew for several minutes with the MCAS firing; the pilot manually counter-intervened each time. It was only when he handed control to a co-pilot that the plane nosedived. Theoretically they could have flown indefinitely while they debugged the problem.

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#56

Post by snarf21 »

mhandley wrote: post #10
mysterydip wrote: post #3

"Instead of relying on a single sensor indicating the angle of the plane’s nose, MCAS will rely on data from both of the plane’s sensors" Why wouldn't you design it that way from the beginning? This isn't Boeing's first plane.

Because if you did that, you'd have to alert the pilots when the AoA sensors disagree and MCAS has been disabled. And you can't do that without training them on what that means, notably how the plane will now fly differently with what you might call "relaxed stability" at high angles of attack. And Boeing really really wanted to avoid retraining of pilots because apparently they had a contract with SouthWest that wou…

Right, they wanted to keep the type rating but it clear flies differently and now we have two crashes and hundreds dead.

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#57

Post by snarf21 »

VBprogrammer wrote: post #2

That's not very surprising to anyone who has been following along. The more interesting question is why they failed to identify the trim runaway condition, or if they did indeed identify it, why the procedure failed to correct it? This is significantly different to the Lion air incident where you can easily give the pilots the benefit of the doubt because the failure mode hadn't been previously identified. The detail…

A major factor in this is that they were told that this plane flies exactly the same as the previous 737. If you do the same "right" things you always do, how are supposed to know things are going badly when you've been lied to from the jump?

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#58

Post by mhandley »

DougBTX wrote: post #51
tyingq wrote: post #38

Earlier quoted context omitted.

Ah, so that indicator would have been abnormally in the "nose down" area after MCAS over adjusted it. Interesting. Information overload, and nobody looked because that amount of auto adjustment wasn't anticipated. And also means they didn't correlate the fairly noisy/visual turning off the wheels to get it in that position.

There was a PDF incident report going around earlier with a chart showing a graph of the inputs from MCAS and the pilots over a period of time. There was a "nose down" command from MCAS, followed by a "nose up" command from the pilot, then a "nose down" command from MCAS, a "nose up" command from the pilot... repeated about 20 times in a row...

The full preliminary report from the LionAir crash is here:

https://www.flightradar24.com/blog/wp-content/uploads/2018/1...

I've put the relevant figure showing the trim adjustments here:

http://nrg.cs.ucl.ac.uk/mjh/lionair.png

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#59

Post by gok »

mhandley wrote: post #10
mysterydip wrote: post #3

"Instead of relying on a single sensor indicating the angle of the plane’s nose, MCAS will rely on data from both of the plane’s sensors" Why wouldn't you design it that way from the beginning? This isn't Boeing's first plane.

Because if you did that, you'd have to alert the pilots when the AoA sensors disagree and MCAS has been disabled. And you can't do that without training them on what that means, notably how the plane will now fly differently with what you might call "relaxed stability" at high angles of attack. And Boeing really really wanted to avoid retraining of pilots because apparently they had a contract with SouthWest that wou…

But don't Southwest planes already have the AoA disagree light, which they bought as an option?

Re: Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

#60

Post by mhandley »

gok wrote: post #59
mhandley wrote: post #10

Earlier quoted context omitted.

Because if you did that, you'd have to alert the pilots when the AoA sensors disagree and MCAS has been disabled. And you can't do that without training them on what that means, notably how the plane will now fly differently with what you might call "relaxed stability" at high angles of attack. And Boeing really really wanted to avoid retraining of pilots because apparently they had a contract with SouthWest that wou…

But don't Southwest planes already have the AoA disagree light, which they bought as an option?

Yes. But the AoA disagree indicator did not disable MCAS. In similar circumstances, SouthWest pilots would not have taken off, because AoA disagree would have indicated as soon as they'd begun their takeoff roll. But if an AoA sensor had failed in flight, it would still have been up to the pilots to manually disable stabilizer trim.
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