Then this is much worse than initially suggested, it means a pilot can be aware of MCAS and still be put in a extremely dangerous position due to the extreme control authority of the module.
I'm not saying that MCAS isn't mostly to blame but the fact that the maximum inputs from the pilot is still lesser than the control authority from the trim raises some serious questions MCAS or not. Had "extend flaps" been at the bottom of the checklist that would have disabled MCAS and likely prevented this crash.
Sure, maybe some complex combination of maneuvers could have helped them out of this but there's really everything pointing the blame at this one system. Pilots did what the boeing manual suggested (even included at the end of this report).
The point still stands, the root cause was MCAS, without it this would never have happened. MCAS would not have pitched them into a dive, and even if they were pitched into a dive by some non MCAS system, they would have been able to turn on electric trim and recover. MCAS both caused the situation, and made fixing it impossible, so it was the root cause of the crash.
Agreed. One could argue that the AoA reading mismatch was the root cause, but the plane alerted the pilots to the discrepancy just as it was meant to (through stick shake and panel readouts).
They were aware of the issue, took measures to mitigate them, and MCAS still drove the plane into the ground.
I didn't say that MCAS wasn't the lions share root cause here. It's just not as simple as the "hurr durr, MCAS bad" that a lot of people keep trying to portray the more nuanced statements of various regulatory agencies as being equivalent to. MCAS might be bad but on an aircraft with a different trim system it wouldn't be "hurr durr" levels of bad.
* 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.
https://en.m.wikipedia.org/wiki/XL_Airways_Germany_Flight_88...
with some similarities to the Ethiopian crash
I don't see in the report that the pilots attempted to both operate the manual trim wheel at the same time. I'm not sure if its explicit in the training, but in the manual its made clear that pilots may need to work together to move the trim out of extreme positions when the electric system is not available, and that doing so will not break the manual trim system.
Releasing the stick to assist with the wheel would have meant allowing the plane to nose-dive. This might have allowed them to crank in the stabilizer in time to recover, but they only had 7,000 feet above the ground to work with.
I could not find if Boeing updated their manuals/checklists after the first crash.
http://www.avioesemusicas.com/wp-content/uploads/2018/10/TBC...
And the FAA made it an emergency airworthiness directive in response.
The steps on it were broadly followed by the Ethiopian flight.
The bulletin completely fails to note that if you don't time the STAB CUTOUT immediately after you use manual electronic control but instead the MCAS acts again before you cutout, you're left trying to manually trim the stabilizers in a situation where the elevators are putting so much force on the jackscrew that manual stabilizer trim may be impossible.
That's what got this flight.
Page 11 of the preliminary report, 05:40:35 "stab trim cut-out".
Page 26, five manual trim up inputs before that time. Manual trim is electric trim instigated with yoke toggle switch.
What is not certain (to me) is if continuous nose up toggle for sure would have inhibited the automatic nose down from MCAS shown at 05:40:45. It really looks like pitch trim still needed to come up more in order to relieve the control column force to bring it back to neutral.
Why didn't they continue to manually trim (electric) after 05:40:35 to relieve yoke back pressure and also to improve climb rate and also reduce speed? I suspect they actually got ahead of themselves, setting trim stab cutoff too soon, not realizing how much more insideous the MCAS upset case is compared to runaway stabilizer trim.
And that is the problem with no training. They had no way to iterate various scenarios of working and failed MCAS behaviors.
The Boeing/FAA directive re: MCAS does not instruct them to extend flaps.
Further, there's other things going on in the cockpit due to the malfunctioning AoA sensor that's the root of all this.
Specifically one of the effects is that they get an Unreliable Airspeed Indication, and run that checklist. That checklists memory items include maintaining the current flap configuration (in this case, flaps up).
The Boeing/FAA directive does not instruct them to deviate from this and extend flaps. They have a checklist memory item instructing them to in fact do the exact opposite, and not touch flaps.
If I'm a 737 MAX pilot, after the Lion Air crash I'm learning absolutely everything I can about MCAS. And from information Boeing provided I would learn that it operates with autopilot off, flaps up, at high indicated AoA.
You mention unreliable airspeed, that was actually their first problem. Flaps were extended at that point, as according to the narrative they were not retracted until after the AoA disagree, stick shaker, and airspeed disagree. In fact it almost reads like they were intending to continue the flight, engage autopilot, and climb to 32,000 ft with the stick shaker going the whole time. That seems very odd to me.
And in a crisis situation you skip the checklists and think fast and apply your instincts because you read something on a forum? Sure if you have a lot of time you can try thinking but this is not debugging a bug where you have hours to observe the issue, try different inputs, observe again, Google some questions etc..
If the checklist doesn't mention flaps and the plane crashes if you keep the flaps up, that's on Boeing.
I guess that there is a max speed for flaps (maybe the computer even actively refuses to extend them if the airspeed is higher than X to avoid that wings are destroyed).
Because the other factors don't single this flight out, and the plane wouldn't have crashed without MCAS misbehaving, or more fundamentally, without the flawed plane design that required such a system in the first place.