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Ethiopian Airlines 737 MAX Investigation Preliminary Report

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Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#331

Post by dang »

crysin wrote: post #233
na85 wrote: post #227

Earlier quoted context omitted.

On HN you can say the same things you say anywhere else but GP didn't couch his rant in fancy synonyms and misused Latin phrases like a priori.

I really like this comment because I agree and was trying to write a comment that said this but not in a toxic way. People act like Hacker News is some bastion of discourse that is raised above the rest of the internet but it's not. Most of the comments I read are people stroking their ego's and enjoying the echo chamber.

Your expectations may be too high. Collective behavior on the internet converges to toxicity. All we can do is mitigate it at the margins and try to slow down the decay. Your help would be appreciated.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#332

Post by Arnt »

AnimalMuppet wrote: post #213
Arnt wrote: post #128

Earlier quoted context omitted.

I've read a couple of these things (strongly recommended — aviation postmortems are a model for us all) and my impression is that "too large" or "slap" are foreign terms in their debugging culture. Their priority list is, AFAICT: 1. Find out what happened. 2. Find out why. 3. Find out how to make sure it doesn't happen again. 4. See point 3. 5. See point 3.

If "why" turns out to be "runaway corporate greed", what do you do for steps 3, 4, and 5? Not that I think that's going to be the result of step 2. It was a contributing factor, probably, but it's not the whole story by any means.

I don't think you would say that if you had read such a report.

The ones I have read do not feature three-word explanations, but rather say things like "the chain of events that led to the accident could have been stopped at any of these single points: and would also have been stopped if both a&b had been done, or if both c&d, or both c&e" and then discuss how each of the many might be changed. They don't say "five of the links in the event chain were at a profit-hungry corporation, whose CEO should be thrown in gaol, then they'll know to do that differently in the future".

"Runaway corporate greed" is fine reason for a quick and angry post on a social network, but aviation postmortems are a different kind of beast, heavy on analysis and prevention, light on anger.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#333

Post by chopin »

dsfyu404ed wrote: post #27
crooked-v wrote: post #19

Earlier quoted context omitted.

MCAS forced the trim to a point where (because of aerodynamics) it was impossible to manually change the trim even after disabling MCAS, and was designed in such a way that it was impossible to engage the electrical trim controls (which could have saved the plane in this case) without also reenabling MCAS.

Flaps out supposedly would have kept MCAS off but the pilots weren't expected to know that.

They were already too fast for that.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#334

Post by chopin »

cjbprime wrote: post #111
brucemoose wrote: post #25

Earlier quoted context omitted.

Layman question -- Does the MCAS system take current height from terrain into account when forcing the nose down?

Nope. (And arguably it shouldn't: a stall at low altitude is much worse than a stall at high altitude, because you lack recovery time. Most fatal stalls begin below 1000ft AGL, which is where this plane was. So your stall avoidance system shouldn't shutdown just because you're at low altitude: that's when you want to avoid stalls.)

MCAS doesn't work in most low altitude conditions as it is switched off when flaps are extended (the case both for departure and landing).

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#335

Post by chopin »

cjbprime wrote: post #276
fgonzag wrote: post #198

Earlier quoted context omitted.

Seriously, a MCAS indicator light (if MCAS is actively issuing commands), a big red button below it called "Disable MCAS" , and a MCAS disabled light (so pilots actually remember when it is disabled) should be more than enough to prevent this. Besides adding the AoA disagree light AND having MCAS use a triple AoA sensor vote to determine the AoA angle.

I think they're not gonna do that because they'd lose the 737 type.

Until they are forced to. I hope that the FAA doesn't get a say here and other agencies will retract the type rating.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#336

Post by chopin »

Arnt wrote: post #332
AnimalMuppet wrote: post #213

Earlier quoted context omitted.

If "why" turns out to be "runaway corporate greed", what do you do for steps 3, 4, and 5? Not that I think that's going to be the result of step 2. It was a contributing factor, probably, but it's not the whole story by any means.

I don't think you would say that if you had read such a report. The ones I have read do not feature three-word explanations, but rather say things like "the chain of events that led to the accident could have been stopped at any of these single points: and would also have been stopped if both a&b had been done, or if both c&d, or both c&e" and then discuss how each of the many might be changed. They don't say "five o…

As the Seattle Times reported, the MCAS system was mis-characterized by Boeing. Rules don't help if you don't go by them.

This postmortem must include "runaway corporate greed" absolutely. Not sure what can be done about it as the FAA is not trustworthy anymore.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#337

Post by VBprogrammer »

msbarnett wrote: post #303
VBprogrammer wrote: post #192

Earlier quoted context omitted.

> I believe that's correct given that they had an Unreliable Airspeed Indicator warning (due to the malfunctioning AoA sensor), per the memory items on the UAI checklist. The idea that a pilot would knowingly leave thrust at climb power while in modestly level flight at low altitude and expect not to overspeed is very strange to me, checklist or no checklist. I think they were too busy fighting the controls to worry…

Setting it to climb is literally a memory item, pictured here: https://aviation.stackexchange.com/questions/24739/what-is-t... . That’s pitch 5 degrees up, thrust at climb at their altitude. Why? Because your instruments disagree about your airspeed. You want to have a large margin to keep your speed high enough that you won’t accidentally stall while you try to establish what’s reliable.

Sure, and you then hold that until the aircraft stalls at 45000ft? Of course not.

You can't point at a memory item and treat it like the pilots can only apply what's in there in exclusion to everything else. The structural limits of the aircraft are there for a reason.

Aside from anything else the pilots were trying to maintain altitude by their communication with ATC.

Not that I'm blaming them. I think they had too much going on to even consider moving the throttles, and thats 100% on Beoing, but it probably didn't help their chances of recovery.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#338

Post by PunchTornado »

Zak wrote: post #180
PunchTornado wrote: post #149

Earlier quoted context omitted.

I don't understand, either you need the MCAS to fly the plane or you don't. If a 737 pilot can operate a 737 MAX only with MCAS, then the pilot shouldn't be able to disable it, right? What if he disables it and then the plane is stalling? There is no MCAS to help.

You don't need MCAS to fly the plane. You don't need ABS to drive a car. Both are designed to counteract erroneous user input based on the readings of fairly simple sensor systems that cannot understand the whole situation and are themselves capable of false readings.

when I drive a car without ABS I don't need a new driving license. Pilots switching to 737 MAX need new flight simulation training, except if the plane has MCAS. See the difference?

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#339

Post by upofadown »

cjbprime wrote: post #319
upofadown wrote: post #305

Earlier quoted context omitted.

Airbus just gives you a joystick with no force feedback at all. So yes ... but an entirely different philosophy. You tell the aircraft what you want it to do and it figures out how to do it. I suppose these recent events could be used as an argument against the idea of doing essentially fly by wire but then putting in a whole lot of extra stuff to make it seem that you are not doing fly by wire.

No, on Airbus the joystick still only moves the elevator, which has less control authority than the stabilizer, which is what trim controls.

It normally moves both as required. A good explanation here:

* https://aviation.stackexchange.com/questions/15268/how-does-...

Even if things degrade all the way down to "direct law" the pilot does not feel any aerodynamic force caused by the trim position.

We are talking about two different interpretations of the word "authority". In the case of the incidents, the pilots were physically unable to overcome the simulated force for an extended time.

Re: Ethiopian Airlines 737 MAX Investigation Preliminary Report

#340

Post by cjbprime »

upofadown wrote: post #339
cjbprime wrote: post #319

Earlier quoted context omitted.

No, on Airbus the joystick still only moves the elevator, which has less control authority than the stabilizer, which is what trim controls.

It normally moves both as required. A good explanation here: * https://aviation.stackexchange.com/questions/15268/how-does-... Even if things degrade all the way down to "direct law" the pilot does not feel any aerodynamic force caused by the trim position. We are talking about two different interpretations of the word "authority". In the case of the incidents, the pilots were physically unable to overcome the simula…

Thanks for the correction! Reading about this brought me to:

https://en.m.wikipedia.org/wiki/XL_Airways_Germany_Flight_88...

with some similarities to the Ethiopian crash

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