Comment by WalterBright
5 hours ago
I know how the stab trim system works. I worked on it (for the 757) for three years.
Yes, it applies to MCAS.
> the symptoms and recovery procedures are distinct
Nope. MCAS failure manifests itself as runaway trim, and the emergency procedures for it are exactly what is needed to recover from it.
1. the stab trim switches override the MCAS signals. Override. That means the pilot can trim to normal using the column mounted trim switches. The column switches will power the trim back to normal. No physical strength is required.
2. there's a "stab trim cutoff" switch on the console. That turns off the trim system. MCAS cannot bypass it.
The proof is the 3rd MCAS incident. The pilots trimmed it back to normal, and turned the stab trim system off.
That's all they had to do.
This is supposed to be a "memory item". The other two crews did not remember the memory item. Boeing even sent out an Emergency Airworthiness Directive reiterating this information. It was ignored by the EA pilots, who did everything wrong (including overspeeding the airplane at full thrust).
The narrative you wrote is the typical one in the mass media, which is utterly wrong. The proof of that is they ignore the 3rd incident which didn't fit the narrative.
I've talked with two 737 pilots about this. They agree with me, though I knew I was right anyway.
Food for thought: ever wonder why the stab trim cutoff switch is in a prominent place on the center console in easy reach?
You just took Boeing adding a secret system that can cause a plane to crash and then blamed the pilots who were unfortunate to be a victim of malfunctioning sensors and then put all the blame on them because pilots who didn't want to die inside a deathtrap aircraft figured out how to avoid their own death the moment they realized that the MCAS crashes were not an isolated incident?
What exactly are you accusing the pilots involved with the accident of? That they had some perverse incentive to die?
> put all the blame on them
Nope. I wrote: "The implementation of it, however, wasn't very good"
> What exactly are you accusing the pilots involved with the accident of?
Not following the runaway stabilizer trim procedure. This is supposed to be a "memory item", meaning a checklist is not required.
There were 3 MCAS incidents:
1. crew trimmed to normal with the thumb switches, then turned off the trim system. Flew the rest of the flight, landed safely.
2. crew trimmed it back to normal at least 11 times (if I recall correctly) and never turned off the trim system. Crashed.
3. Boeing Emergency Airworthiness directive was sent to all MAX pilots. In a nutshell, it says to restore normal trim using the thumb switches then turn off the trim system. EA pilots instead turned off the trim system while the airplane was pointed down at full throttle. Crashed.
The two 737 pilots I talked to about this both asserted pilot incompetence.
Personally, I assign half the blame on Boeing and the other half on the pilots. Flying is not a joke. Not paying attention to an Emergency Airworthiness Directive is not acceptable.
> "The implementation of it, however, wasn't very good"
It was purposefully deceptive -- Boeing management actively decided to hide its existence from pilots.
The narrative that the pilots were at fault was Boeing leadership covering their ass.
The MCAS symptoms did not match runaway trim. It's not continuous. It stops and starts.
MCAS would also re-activate with a five second delay, just long enough to confuse pilots.
More importantly, deactivating the electrical trim system would make it all too easy to enter a regime where the pilots couldn't physically recover the plane.
This is a Catch-22 scenario: Activate the electrics and be killed by MCAS, or deactivate the electrics and be killed by physics.
I could go through each of your comments in this thread and point out how NTSB crash investigators proved that Boeing was directly or indirectly at fault in almost every aspect, but I don't want to write out ten pages. Others have done so already, more eloquently, and often with more colourful language. Most professional pilots were rightly furious with Boeing.
Boeing's arguments have been mutually exclusive with each other: "Just remember how to operate MCAS... which we hid from you!" and "Just disable the electric trim... which will pit you against forces you can't overcome"... "Which is not a problem because you can turn electric trim back one... but then MCAS will try to kill you again"... "It won't do that because it is dual redundant... an option... that nobody purchased... and we didn't even tell most customers about."
I expect this kind of self-contradictory "logic" from narcissists and sociopaths -- I know one of each and I'm now intimately familiar with the self serving arguments that make no sense, especially in combination.