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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

#71

Post by CaptainZapp »

saiya-jin wrote: post #63
ams6110 wrote: post #52

Earlier quoted context omitted.

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.

Which was far from enough as we can see. Full retraining and perhaps other actions should have happened immediately so Boeing could hold any form of moral high ground here. When it comes to mass transport, safety should definitely have higher priority than pushing some potentially new cool tech ASAP (which is debatable, making plane unstable ain't cool by any measure)

And they're still draging their feet on the retraining issue.

No simulator time required, no sire!

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

#72

Post by VBprogrammer »

chopin wrote: post #50
VBprogrammer wrote: post #37

Earlier quoted context omitted.

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.

But this directive said "handle like a trim runaway". However MCAS may present itself differently from a trim runaway when failing. Furthermore a failing sensor may activate the stick shaker and the last thing a pilot is trained to do is pull up in such a situation. So you might get: - unreliable airspeed warning - stick shaker (=stall is imminent) So you don't know your airspeed (otherwise you can conclude you're sa…

The full list of potential indications is included in the AD. It also describes the operation of the trim system under MCAS control.

You can see them in the Lion Air preliminary report linked above.

Pilots are trained to deal with partial panel situations. The mantra is pitch + power = performance. In VMC this should be well within the capibilities of a normal pilot, put the nose on the horizon and set something like 65% power.

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

#73

Post by ams6110 »

linuxftw wrote: post #68

Still doesn't answer the question of, why if MCAS is required during critical portions of the flight to prevent stalling is disabling of MCAS an acceptable solution for this aircraft? Introducing a new condition of "We think MCAS is on, but we're not quite sure / it's cutting in and out due to censor disagreements" is preposterous.

This might be splitting hairs, but MCAS is not there to prevent stalling. It's there to meet a specific certification requirement on control stick forces at high angles of attack. Yes the intent of the requirement is to reduce the tendency of the pilot to pitch up too much near the stall. But MCAS doesn't prevent stalling.

Modern aircraft have many automatic systems that are there to make the pilot's job easier. That doesn't mean they are unsafe to fly if those systems malfunction and have to be disabled.

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

#75

Post by [deleted] »

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.

[deleted]

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

#76

Post by chasingthewind »

armitron wrote: post #65

I'll never fly 737 Max. No matter what changes they do, barring a complete redesign of the plane. Boeing deserves to go out of business for this.

I'm not going to defend Boeing's conduct here for one moment, but I do think your statement is an over-reaction. The company employs 150,000 people, it contributes billions to the US economy, and builds significant aerospace know-how in the US. I imagine we could come up with lots of reasons why Boeing is a net positive. These crashes are tragic and Boeing's conduct deserves condemnation, but a solution that keeps the company going and fixes the culture that led to this seems to be a far better solution than them going out of business entirely.

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

#77

Post by mannykannot »

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.

When things go wrong, information overload is a problem.

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

#78

Post by petilon »

zaxomi wrote: post #22
sergiosgc wrote: post #14

Earlier quoted context omitted.

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.

No, it is not unstable without MCAS. MCAS is only designed to change the trim if the airplane is hand flown in flaps-retracted, low-speed, nose-up flight. This is something almost everyone is missing: A normal flight should not encounter this.

>> A normal flight should not encounter this.

What is your source? This is not what I have been reading. What I have been reading is that the MAX has a bigger engine and this engine has been positioned forward on the wing in order to preserve ground clearance. As a result of this unusual engine position, the MAX has a tendency to pitch up during acceleration. Nowhere did I read that this doesn't happen during normal flights.

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

#80

Post by ams6110 »

yg6ht5 wrote: post #39
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…

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

Well, that's per plane. And Southwest has ordered hundreds of them.
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