This is very important, as it shows the ratio of pilots aware of the mitigation is low, and/or the stress of fighting with the the computer makes you forget you training amendments
What people (including pilots) do under stress is resort to simple actions drilled in by training. That's why emergency procedure training is a major part of pilot training curriculum.
What goes away first under stress is capability for complex reasoning, which is what one would need to figure out what the heck is going on and take appropriate action. In this case an a/c doing uncommanded dive can be a result of three things: elevator controls malfuncion (unlikely in modern jets, the mechanisms for transmitting control forces from the yoke to the elevator are multiply redundant and well-understood to be critical), structural breakdown (empennage falling off would do that), or run-away elevator or stabilizer trim.
In most a/c the runaway trim can be only caused by malfunctioning auto-pilot (that's why APs have multiple redundant ways to disable them), so the pilots faced this situation react by trying to disable AP in all available ways and then immediately jumping to conclusion that there's something catastrophically wrong with elevator system or even airframe integrity. The thought that there could be yet another system which can do major trim adjustment doesn't even enter their consciousness.
Training (and/or being in a position where there's no immediate stress of wrangling misbehaving a/c) would help to get to the correct solution (disabling trim motor by pulling the circuit breaker).
That said, flying an a/c seriously out of trim is hard, and can cause an accident on its own (the fine pitch control is gone, and you can even be so far out of trim that you cannot do landing flare no matter how hard you pull up, which in heavy jets would result in structural breakdown when the plane slams into runway).
My question is why doesn't the "omg something is seriously fucked up give me manual control NOW" button disable the MCAS as well? That seems like a UX failure.
That would be the autopilot disconnect button or, in this case, the trim switch, the pressing of which is the correct immediate response to this occurrence, followed by the disabling of the system using switches on the center pedestal. While it's certainly hazardous for Boeing to knowingly expose pilots to this occurrence, I'm also conflicted by the fact that they failed to respond properly. The procedure is similar on Boeing, Airbus, Embraer and Bombardier aircraft. Standardized, in a way.
MCAS is designed to work only with autopilot disengaged. With autopilot and autothrottle engaged there would be similar logic at play because the general goal would be to not have the automation induce a stall. With everything disabled there is a risk that applying full throttle will result in the airplane pitching up dramatically beyond the ability of the elevator to pitch the airplane back down and potentially inducing a stall. This is an inherent problem with putting big engines under the wing (and is a problem in the 737 Classic[0], NG, and MAX).
You could almost certainly disable just about anything by pulling the appropriate circuit breaker. You don't want to do that because the plane may be left in a state where you can't control it manually and you only have a few thousand feet of altitude to recover.
There are, in fact, two switches to turn off the electronic control of the horizontal stabilizer. The previous Lion Air crew used them after the pilot riding in the jumpseat went back and grabbed his copy of what I'd assume was the flight manual and had an ah-hah moment[1]. The flight 610 crew were pouring over something (quick reference handbook?) but didn't express any awareness of the stabilizer being trimmed[2].
Depending on how bad things got there are a few problems with this. First, electrically moving the stabilizer is much faster than moving it manually. MCAS can operate at two speeds, IIRC both are slower than the speed dictated by the buttons on the yoke (plus the buttons on the yoke will pause MCAS). But even MCAS will move the stabilizer much faster than a pilot could by cranking the manual wheels. I believe that moving the stabilizer from one extreme at the fastest speed to the other takes about a minute. You can find videos of the stabilizer mechanism on a 777 on youtube, it's just not something that's designed to move quickly.
The next problem is that if the stabilizer is pitched down sufficiently (perhaps by MCAS), your first instinct may be to pull back on the yoke (to move the elevator) to regain pitch. Well, once you've done that the aerodynamic forces may be such that you can't move the stabilizer into a nose up position until you let go of the yoke and let the plane pitch down further (Boeing references needing to unload the stabilizer in some documents). That's something you've gotta have cat-like reflexes for when you're already flying so low.
The really sad part is that the pilots could have disabled MCAS and retained electric control over the stabilizer by extending the flaps. But how are the pilots going to know this when Boeing refused to document anything?
Thank you for your post. I've read that Boeing removed the "yoke jerk" function on the 737 MAX. The flight 302 PIC might have been trying to use it and I have not read whether that functional change was clearly explained to pilots. Many commentators don't seem to realize the extreme low altitude at which this particular struggle was occurring.
>The pilots of a doomed Lion Air Boeing 737 Max scoured a handbook as they struggled to understand why the jet was lurching downwards, but ran out of time before it hit the water, three people with knowledge of the cockpit voice recorder contents said. (straitstimes)
I can't help thinking things would be safer and the Ethiopian crash may not have happened if they just published all the info rather leaving this kind of thing to anonymous leaks to the press.
If they had published this info, then they couldn't have sold the jet to airlines as just another 737 that any other 737-rated pilot could fly without additional training.
Boeing was right not to document anything, because then they might have to get a new certification (which is very expensive) for the plane, and pilots would need more training, which would make it hard or impossible for them to sell this plane to airlines as "just another 737".
Remember, a few fatal crashes are worth it as long as it means higher corporate profits.
Well, there is no such button. Perhaps there should be though a better solution might be to fix the automation. Airbus planes seem to work ok without a button but don't have a crash the plane if one sensor fails system.
There an AirFrance (Airbus) flight a few years back that crashed over the Atlantic that was partially the result of a stuck pitot tube. I remember at the time one of the debates was how automated Airbus planes were over Boeing. Pilots seemed split as to which system they preferred, but generally wanted more control, not less.
No, under normal conditions the MAX isn't unstable. The instability comes only at high angles of attack (close to stalling) and only there the MCAS system should kick in. It was meant to be the equivalent to ESP systems in cars.
Do we know, exactly, how much of the 737 Max 8's flight envelope was lost compared to earlier models? I'm getting the feeling that the instability happens far closer to the regular maneuvering envelope than is being alluded to in the press.
It's a single data point / anecdote. These investigations are incredibly thorough, precise, and authoritative so it makes sense they'd seek to exclude that kind of information until they knew for sure.
And a very relevant one, in this case: trim runaway with pilots not understanding it's a runaway. The visiting pilot does recognise the situation and restores expected flight dynamics. What went wrong, why did not two pilots realise something that is traditionally a known case and well understood? Because it didn't look like a traditional case.
An irrelevant one in this case. This report needs to find out the technical/training/... reason, not why the other pilot needed a ride. I'm sure they'd have included it if they wanted to recommend having three pilots on every flight.
One data point may lead you to bad conclusions, like in this case "one third of pilots don't know how to disengage the MCAS" -- the fact is we don't know what ratio. It might be higher, it might be lower, but one data point isn't valuable or thorough. In the preliminary report they mentioned someone else disabled it. In their final, I'm sure we'll get the details.
It also shows that pilot awareness (and therefore training) should have been sufficient. The key deficiency here was Boeing's. The agency not disclosing this detail is a problem too.
I think you misunderstood. Had the pilots been trained, they could have dealt with it -- that the off-duty pilot was able to shows it was possible to respond correctly, while that the others weren't shows the lack of training is a real problem.
Thanks, I see. I don't think it does much good to notice that a small percentage of pilots can be capable of figuring it out, if they have no other duties at the time.
That doesn't tell us that it's reasonable to expect pilots in command under stress to always figure it out. And they have to figure it out 100% of the time to avoid statistically unacceptable crashes. So I don't agree that pilot training is an acceptable answer given what we know so far.
Yes it does: it shows that there is a procedure that would have worked had the pilots recognized the issue and known about the procedure.
The pilots were stressed in part because they didn't know -- they had plenty of time to recognize the issue and take action had they known, but they didn't, so no amount of time would have helped them. We don't know if one more thing to know about would too much, but I rather doubt that.
Edited to add it’s a training amendment