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U.S. FAA proposes requiring key Boeing 737 MAX design changes

reuters.com

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Re: U.S. FAA proposes requiring key Boeing 737 MAX design changes

#251

Post by WalterBright »

acqq wrote: post #230
bkor wrote: post #192

Earlier quoted context omitted.

A crash is not due to one cause. Multiple things have to fail for this to be a problem. Blaming pilots is way too simplistic. The design of those warnings were highly confusing and overwhelming. Saying "oh, just have better pilots" it NOT good enough. It should be as per the Swiss cheese theory where multiple things should fail before there's a problem. Further, not hide things like MCAS, downplay the need for additi…

> it was the pilots not reading a message. It was that the message (see the whole, the link was quoted) definitely wasn't clear . It has multiple weasel words and it is far from a clear and actionable sequence checklist for the exact condition in which two planes were put due to the MCAS. Only with the hindsight of knowing how two accidents developed and the independent pilots trying to reconstruct on the simulators…

It's written in airplane jargon, of course, but it's plenty clear.

> It's Boeing who insisted that the training for MCAS is not needed.

It's not completely unreasonable to expect the pilots to be able to handle runaway trim, especially given an EMERGENCY AIRWORTHINESS DIRECTIVE reiterating how to do it. Runaway trim is a critical problem, which is why the electric trim switches are there as well as the cutoff switches, all in easy reach. Dealing with this is supposed to be a "memory item", meaning something the pilots must know.

But clearly in hindsight, dealing with runaway trim must be specifically and better trained for.

> special training

The thing about runaway trim is it turns on when it's not supposed to. That's why the electric trim overrides are there and the cutoff switches. Those are there for all Boeing jets since electric trim was installed going back to at least 1960 and probably much earlier.

When I worked on the stabilizer trim system on the 757, I worked mostly on the gearbox, but was peripherally involved with the electrical system for it. The cutoff switches were there for "when demons possess the control system and try to drive you into the ground."

Re: U.S. FAA proposes requiring key Boeing 737 MAX design changes

#252

Post by WalterBright »

misanthropian00 wrote: post #218
WalterBright wrote: post #160

Earlier quoted context omitted.

The EA pilots were given an Emergency Airworthiness Directive which gave a two step process for recovering from MCAS malfunction: 1. use the electric trim switches to drive the trim to normal 2. cut off the trim system with the console cutoff switches. That's it. As simple as that. And it is NOT what the EA pilots did (they cut off the trim first). Here are the exact directions: "Initially, higher control forces may…

https://aviation.stackexchange.com/questions/61203/what-is-t... That article I think summarizes the state of the pilot error arguments back when people were still discussing this online. Two methods of disabling an out of control MCAS were mentioned but only one would actually work with a faulty AoA sensor: lowering the flaps. I wonder why Boeing did not mention just lowering the flaps to disable MCAS in an emergency…

> This is actually the first I've heard anyone mention the simple method of using the electric trim to fight MCAS until reaching a neutral trim and only then hitting CUTOFF, but would this still work if you were already at max trim and heading nose down toward the water?

Yes, and it did indeed work. The pilots, though, did not cut off the stab trim.

> This method seems to depend on the electric trim being fast enough to fight MCAS to a neutral or near neutral trim even from a maxed trim stab position. Is it fast enough to do that?

Yes, and it doesn't "fight" MCAS. It overrides it electrically in hardware (not software).

> I'm less sure about your method of just electric trimming to neutral and then hitting CUTOFF because the electric trim adjustment would have to be fast enough to overcome the MCAS counter-adjustments. Surely electric trim would not have been designed for such a race.

I'm sure about it. The electric trim moves just as fast as the MCAS would, because the trim is electrically ON or OFF. There's no speed control on it. It's not a race, either. The electric trim switches are between the MCAS and the motors, they override it.

Furthermore, in the LA flight before the LA crash flight, the same problem happened. The pilots restored trim and hit the cutoff switches, and landed safely. The mystery to me was why that airplane was allowed to take off again before being repaired.

> And also that seems like such an obvious thing to do even if you haven't read the airworthiness directive you cite. Something is messing with the trim. There is a button that adjusts trim ffs. Why not try to just hold it down? Even a child might think of that simple solution. But these pilots didn't? Some of them were even experienced.

Exactly, and that's what the pilots did in the first non-crashing incident.

> Probably the Ethiopian pilots were unaware of the airworthiness directive

Yup, and that was a contributing factor to the crash.

Re: U.S. FAA proposes requiring key Boeing 737 MAX design changes

#253

Post by Sebb767 »

zrobotics wrote: post #238
Sebb767 wrote: post #231

Earlier quoted context omitted.

> In other words, if the odds are e.g. 1 in 10 that the trip will kill me, I don't give a shit how low the risk per mile is. The average distance to mars is about 225 million km, so that would be one accident about every 2,2 billion km or 0.45 deaths per km, which is a bit deadlier than buses and 9 times as deadly as planes. Gives some perspective on how save planes actually are.

You might want to check your figures- 1 death/2.2e9 km is 4.5e-10 deaths per km. The 0.45/km figure is way out, for that to be the case there would need to be roughly 1.1billion deaths per 2.2 billion km.

Yes, this was in deaths per billion km - sorry, should've specified.

Re: U.S. FAA proposes requiring key Boeing 737 MAX design changes

#254

Post by acqq »

WalterBright wrote: post #251
acqq wrote: post #230

Earlier quoted context omitted.

> it was the pilots not reading a message. It was that the message (see the whole, the link was quoted) definitely wasn't clear . It has multiple weasel words and it is far from a clear and actionable sequence checklist for the exact condition in which two planes were put due to the MCAS. Only with the hindsight of knowing how two accidents developed and the independent pilots trying to reconstruct on the simulators…

It's written in airplane jargon, of course, but it's plenty clear. > It's Boeing who insisted that the training for MCAS is not needed. It's not completely unreasonable to expect the pilots to be able to handle runaway trim, especially given an EMERGENCY AIRWORTHINESS DIRECTIVE reiterating how to do it. Runaway trim is a critical problem, which is why the electric trim switches are there as well as the cutoff switche…

> The cutoff switches were there for "when demons possess the control system and try to drive you into the ground."

For the second crash it wasn't about "hit the switch" at any moment you will when you notice the problem. It was: "unless you are lucky to hit the switch in a very special moment, you won't be able to regain the control of the plane at all." Not in the message, not trained, and even some pilots learned that only later in the reconstruction of the crash on the simulator.

Re: U.S. FAA proposes requiring key Boeing 737 MAX design changes

#255

Post by WalterBright »

acqq wrote: post #254
WalterBright wrote: post #251

Earlier quoted context omitted.

It's written in airplane jargon, of course, but it's plenty clear. > It's Boeing who insisted that the training for MCAS is not needed. It's not completely unreasonable to expect the pilots to be able to handle runaway trim, especially given an EMERGENCY AIRWORTHINESS DIRECTIVE reiterating how to do it. Runaway trim is a critical problem, which is why the electric trim switches are there as well as the cutoff switche…

> The cutoff switches were there for "when demons possess the control system and try to drive you into the ground." For the second crash it wasn't about "hit the switch" at any moment you will when you notice the problem. It was: "unless you are lucky to hit the switch in a very special moment, you won't be able to regain the control of the plane at all." Not in the message, not trained, and even some pilots learned…

The EAD was quite clear. Trim back to normal with the electric trim switches, then shut off the trim.

There is nothing confusing about that. There is no "very special moment". There is no "you won't be able to regain control at all".

The proof of what I say is in the first LA incident (the one that didn't crash). The pilots trimmed back to normal a couple times with the electric trim switches, then hit the cutoff switches, and landed safely without incident.

In the second LA incident, they trimmed back to normal 25 times, never thought to cut off the trim system, and crashed on the 26th time.

Re: U.S. FAA proposes requiring key Boeing 737 MAX design changes

#256

Post by top_sigrid »

jacquesm wrote: post #42
josemanuel wrote: post #2

I wonder what EASA will do..

Run their own evaluation and make their own set of recommendations. With some luck they will not be incompatible with each other.

Do you know that this is happening? I thought they were mostly following the FAAs ruling. Is it certain that this will change in the future or even for the certification of the 737 Max?

Re: U.S. FAA proposes requiring key Boeing 737 MAX design changes

#257

Post by strogonoff »

Nacdor wrote: post #6

Given the option, would anyone choose to book a trip on one of these new Boeing aircraft rather than anything else? I know I wouldn't, my family wouldn't, and none of the friends or co-workers I've discussed this with would. Something tells me airlines are going to be making it even more difficult to determine which aircraft you'll be flying on when you book a ticket. As far as I know they're not required to tell you…

> would anyone choose to book a trip on one of these new Boeing aircraft rather than anything else?

To me getting to/from the airplane (any model) is usually of significantly more concern[0] than flying itself, so the only reason I would actively choose a specific airplane is if I get to fly in a new or interesting model. So there, you have a definite yes from me.

[0] Traffic accidents, possibility of losing possessions, issues at immigration, untrustworthy taxi drivers, etc.

Re: U.S. FAA proposes requiring key Boeing 737 MAX design changes

#258

Post by salawat »

LoSboccacc wrote: post #214
Someone1234 wrote: post #87

Earlier quoted context omitted.

> they can lock out the bad one as an input to the MCAS The 737 MAX didn't support that as delivered. Even with the warning (which some US airlines paid for), you couldn't "lock out the bad one" even assuming you knew which one that was (you don't). All you could do is disable the electronic horizontal stabilizer completely, so that MCAS couldn't command it into a dangerous and unrecoverable state. MCAS has been fixe…

> Half measures are exactly how we got to this point also they increased the maximum stabilizer angles mcas could command, the review/certification was done with a 0.6 cap (effective but not overwhelming) and on production it was increased on a whopping 2.5 degrees. it was also meant to be using vertical acceleration to understand whether the plane was actually stalling, but that trigger was removed it was also suppo…

Impedance mismatch I believe they call that in the Electrical Engineering world. If you don't match up your output characteristics to the specified input characteristics of the next circuit element, you're hosed.

Re: U.S. FAA proposes requiring key Boeing 737 MAX design changes

#259

Post by acqq »

WalterBright wrote: post #255
acqq wrote: post #254

Earlier quoted context omitted.

> The cutoff switches were there for "when demons possess the control system and try to drive you into the ground." For the second crash it wasn't about "hit the switch" at any moment you will when you notice the problem. It was: "unless you are lucky to hit the switch in a very special moment, you won't be able to regain the control of the plane at all." Not in the message, not trained, and even some pilots learned…

The EAD was quite clear. Trim back to normal with the electric trim switches, then shut off the trim. There is nothing confusing about that. There is no "very special moment". There is no "you won't be able to regain control at all". The proof of what I say is in the first LA incident (the one that didn't crash). The pilots trimmed back to normal a couple times with the electric trim switches, then hit the cutoff swi…

> The EAD was quite clear. Trim back to normal with the electric trim switches, then shut off the trim.

I don't see that wording anywhere in EAD. Only the quoted weasel worded sentence. It's your interpretation post-crashes and their analysis that they were supposed to do exactly that in exactly that order. Or do you have some other quote? The mental model the pilots were trained to was "if the electric doesn't work, switch it off, trim manually." The MCAS changed that to: 1) electric will work, but MCAS "invisible ghost" will pause to confuse you that the controls work and only then undo whatever you managed to do. 2) There's only one position in which turning off the switch was safe, under their circumstances -- switching to manual trim outside of the "normal" was a practical death sentence, also nowhere written.

So, as far as I see, not only your "clear" sequence was nowhere written that clear, the mental model that the pilots had to have changed completely, but without training, and the safe procedure to escape was figured out only after looking at the logs of two crashes.

That it is "clear" to somebody sitting in the armchair with the crash logs and having all the time in the world to think about it after all that happened doesn't mean that those who survived had such clearness, just that they had luck.

Re: U.S. FAA proposes requiring key Boeing 737 MAX design changes

#260

Post by WalterBright »

acqq wrote: post #259
WalterBright wrote: post #255

Earlier quoted context omitted.

The EAD was quite clear. Trim back to normal with the electric trim switches, then shut off the trim. There is nothing confusing about that. There is no "very special moment". There is no "you won't be able to regain control at all". The proof of what I say is in the first LA incident (the one that didn't crash). The pilots trimmed back to normal a couple times with the electric trim switches, then hit the cutoff swi…

> The EAD was quite clear. Trim back to normal with the electric trim switches, then shut off the trim. I don't see that wording anywhere in EAD. Only the quoted weasel worded sentence. It's your interpretation post-crashes and their analysis that they were supposed to do exactly that in exactly that order. Or do you have some other quote? The mental model the pilots were trained to was "if the electric doesn't work,…

Um, I worked on the 757 stab trim design for 3 years. I'm not an armchair quarterback here. An EAD is not a document where you look for loopholes, parse linguistics, and debate angels dancing on pinheads. Take the straightforward meaning, add it to the information a pilot already knows, and it makes perfect sense.

P.S. your version of what the words mean is solely your invention. I've shown this text to many people, and none have come close to your creative version. This includes pilots.

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