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?

0: http://avherald.com/h?article=419f2f9e

1: https://www.grid.id/read/04966850/deretan-kejanggalan-yang-d...

2: https://www.straitstimes.com/asia/se-asia/cockpit-voice-reco...

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.

I think I saw that movie. "Fight Club"? Or was this the less well known sequel, "FLIGHT Club"?

That's very informative, thank you.

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.

https://en.m.wikipedia.org/wiki/Air_France_Flight_447

That's an excellent question, and will likely be one of the conclusions of the accident investigations.

Could be related to the issue that MAX is unstable in flight with that system off. Unlike previous 737s.

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.

Yep. Except that the "exceptional" conditions under which the MCAS kicks in can also "occur" (=seem to occur) due to sensor failure.

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.