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Preliminary conclusion MCAS misfired in Ethiopian's 737 max crash

cnbc.com

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

#11

Post by tapland »

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.

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

#12

Post by kristofferR »

Moru wrote: post #8
kristofferR wrote: post #7

Earlier quoted context omitted.

They did, but the redundancy was a premium add-on feature.

No, the extra sensor was add-on feature. It still wasn't redundant for the MCAS, just an indicator for the pilots.

Wow, that's even worse...

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

#13

Post by isolli »

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…

Related question: how does regulatory approval of planes work, worldwide? I read a few times that the FAA had approved the new plane too quickly, but don't other regulators have their word?

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

#14

Post by sergiosgc »

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.

Worse. Why don't they do it with three sensors and a voting system? By using two sensors, when they disagree, MCAS will have to be disabled. It seems the plane is unstable without MCAS, due to the forward positioning of the engines, requiring specific training and abilities from pilots.

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

#15

Post by mhandley »

Moru wrote: post #8
kristofferR wrote: post #7

Earlier quoted context omitted.

They did, but the redundancy was a premium add-on feature.

No, the extra sensor was add-on feature. It still wasn't redundant for the MCAS, just an indicator for the pilots.

All 737s have two AoA sensors - they're used for several purposes, not just MCAS. Originally MCAS used only one of the two sensors, though it alternated which one with each flight. The optional features were an AoA disagree indicator, and the AoA data itself being displayed on the cockpit displays. Having either optional feature didn't change the fact that MCAS only used one sensor.

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

#16

Post by mastazi »

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...

The little "web" link under the title of every HN post does that for you :-)

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

#17

Post by sundvor »

mastazi wrote: post #16
1f60c wrote: post #9

Earlier quoted context omitted.

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...

The little "web" link under the title of every HN post does that for you :-)

Oh didn't know that one - thanks!

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

#18

Post by [deleted] »

sergiosgc wrote: post #14
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.

Worse. Why don't they do it with three sensors and a voting system? By using two sensors, when they disagree, MCAS will have to be disabled. It seems the plane is unstable without MCAS, due to the forward positioning of the engines, requiring specific training and abilities from pilots.

[deleted]

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

#19

Post by Svip »

isolli wrote: post #13
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…

Related question: how does regulatory approval of planes work, worldwide? I read a few times that the FAA had approved the new plane too quickly, but don't other regulators have their word?

FAA have (or had) such a good record, that other regulators, like EASA, simply trusted a FAA certification. In the same way, FAA trusts an EASA certification for an Airbus plane.

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

#20

Post by sokoloff »

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.

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 runaway continues) “trim wheel x grasp and hold”

All of those are “above the line, memory items” which the crew must be able to recall and execute prior to referencing the checklists in the QRH.

Boeing has some significant fault here, but I’d expect a full performance crew to handle this emergency and suspect the CVR and FDR data will show them in a less than fully flattering light, especially after Lion Air, the emergency AD, safety memos, and general publicity surrounding the previous crash.

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