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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

#31

Post by mhandley »

VBprogrammer wrote: post #26
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…

It's worth noting that there are other more engineering reasons it could be tricky to use both. An aircraft in a side slip will show different reading on the left and right sensors. Also, there are failures which are likely to impact both at much the same time, icing being a big one.

Agreed. Boeing's revised MCAS will disable itself if the AoA sensors disagree by more than 5.5 degrees when MCAS activates, or a sustained difference of more than 10 degrees otherwise. This is to take into account the fact that the sensors disagree to some degree in normal circumstances. These are fairly relaxed limits, but does demonstrate that a reasonable solution is possible.

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

#32

Post by obituary_latte »

1f60c wrote: post #9
marksomnian wrote: post #4

Paywalled, anyone have a workaround?

Simply search for the title on Google, and they’ll let you in based on that. https://www.google.com/search?q=Investigators+Believe+Boeing...

This didn’t work for me (neither did the “web” link under op title). Wonder if it was because I’d already visited?

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

#33

Post by userbinator »

tyingq wrote: post #27
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…

The layperson in me wants to know why things like trim don't have a meter/display that shows the actual setting. Seeing +6/-6 seems like it might trigger recognition of runaway adjustment.

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.

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

#34

Post by [deleted] »

userbinator wrote: post #33
tyingq wrote: post #27

Earlier quoted context omitted.

The layperson in me wants to know why things like trim don't have a meter/display that shows the actual setting. Seeing +6/-6 seems like it might trigger recognition of runaway adjustment.

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.

[deleted]

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

#35

Post by ptero »

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.

It is possible that it was clear from the start that this is the right way to go, but a modern plane is a very complex and highly regulated piece of equipment. Even minor changes could have a long tail of ramifications for operation (some of those have been noted, such as likely very different performance when crabbing at crosswinds).

I am not saying that Boeing did not try to cut corners (I just do not know), but the current media circus painting Boeing as a bunch of [idiot engineers | greedy execs | lazy testers] is likely far from reality or at least a major oversimplification. Boeing planes (including 737 max) are still very safe (compare to cars). Mistakes should be calmly assessed and fixed and making a public circus of this simply pushes engineers to avoid everything but uber-conservative, uber-safe solutions, which has major costs in itself. My 2c.

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

#36

Post by CaptainZapp »

ptero wrote: post #35
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.

It is possible that it was clear from the start that this is the right way to go, but a modern plane is a very complex and highly regulated piece of equipment. Even minor changes could have a long tail of ramifications for operation (some of those have been noted, such as likely very different performance when crabbing at crosswinds). I am not saying that Boeing did not try to cut corners (I just do not know), but th…

What I think they're absolutely and criminally guilty of is to not ground the plane after the first crash.

Instead they wasted time and resources to smear the airline and the pilots.

And that's inexcusable.

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

#37

Post by VBprogrammer »

cm2187 wrote: post #29
tapland wrote: post #11

Earlier quoted context omitted.

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

I am not talking about these specific pilots about which I know nothing. But not every single commercial pilot is passionate about his job. For some it is just a day job and until they are asked to do a particular training, may not even be aware that MCAS even exists. Think professional developers (granted the bar is infinitely lower). You would assume no one would introduce a SQL injection vulnerability in new code…

That would be a huge failing on behalf of the airline. There was an emergency airworthiness directive which should have brought this to the attention to all pilots of these aircraft even if they somehow missed all of the other coverage.

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

#38

Post by tyingq »

userbinator wrote: post #33
tyingq wrote: post #27

Earlier quoted context omitted.

The layperson in me wants to know why things like trim don't have a meter/display that shows the actual setting. Seeing +6/-6 seems like it might trigger recognition of runaway adjustment.

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.

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

#39

Post by yg6ht5 »

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…

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

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

#40

Post by ams6110 »

CaptainZapp wrote: post #36
ptero wrote: post #35

Earlier quoted context omitted.

It is possible that it was clear from the start that this is the right way to go, but a modern plane is a very complex and highly regulated piece of equipment. Even minor changes could have a long tail of ramifications for operation (some of those have been noted, such as likely very different performance when crabbing at crosswinds). I am not saying that Boeing did not try to cut corners (I just do not know), but th…

What I think they're absolutely and criminally guilty of is to not ground the plane after the first crash. Instead they wasted time and resources to smear the airline and the pilots. And that's inexcusable.

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?
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