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NEWS 737MAX

xj220

Will fly for food.
pilot
Contributor
The other issue is that a single AoA vane failure should not result in activation of MCAS the way it did.
 

wink

War Hoover NFO.
None
Super Moderator
Contributor
Wasn’t it a problem with the AOA probe? Surely they’d seen one of those before. That malfunctioning AOA probe caused MCAS to do what it was designed to do.

Also, if Lion Air mechanics didn’t understand how to fix the problem or have the parts necessary to fix it, then the mechanics should have said so and that plane shouldn’t have been flying again.

I believe the software fix isn’t to remove MCAS, it’s to limit how the degree to which it moves the pitch trim. The crews could have been alerted to the AOA disagree, but the airline elected to not have it installed.
First, as the investigation in either case is not complete, we don't know it was a malfunctioning probe. Second, if mx didn't know about MCAS like the pilots, they may not have associated the runaway trim with the AOA vane. In any case, the vane itself may not have been bad, certainly to look at it. Electronic signals and software are all down stream of the physical device.
 

SlickAg

Registered User
pilot
First, as the investigation in either case is not complete, we don't know it was a malfunctioning probe. Second, if mx didn't know about MCAS like the pilots, they may not have associated the runaway trim with the AOA vane. In any case, the vane itself may not have been bad, certainly to look at it. Electronic signals and software are all down stream of the physical device.
“On 7 November, the NTSC confirmed that there had been problems with Flight 610's angle of attack (AoA) sensors. Thinking that it would fix the problem, the engineers in Bali then replaced one of the aircraft's AoA sensors, but the problem persisted on the penultimate flight, from Denpasar to Jakarta. Just minutes after takeoff, the aircraft abruptly dived. The crew of that flight, however, had managed to control the aircraft and decided to fly at a lower than normal altitude. They then managed to land the aircraft safely and recorded a twenty-degree difference between the readings of the left AoA sensor and the right sensor.”

 

scoolbubba

Brett327 gargles ballsacks
pilot
Contributor
So you are saying because if you can overpower the UNCOMMANDED nose down trim with nose up trim from the yoke, it isn't runaway trim? I have reviewed my 737 QRH ( been off too long to recall it ) . I fail to see how one would not think Runaway Stab Trim was anything but the logical way to go in a MCAS abnormal. No other procedure comes close to applying.

I am saying no by the condition in my current QRH for runway stab trim: Uncommanded stabilizer trim movement occurs continuously. If the trim can be interrupted by nose-up inputs, it's by definition not continuous.

You and I both know the stab trim system well enough to know that if it isn't doing what we want it to do, we can turn it off with 2 switches. That requires us to completely go outside our 121 training that is Boeing/airline specific dummy proofing an EP and forcing you to work from immediate actions > QRC > QRH. Step 5 of our QRH procedure finally gets to turning the stab trim off.

Now, work through that with a 200 hour copilot who doesn't have the 'ahh fuck it turn that shit off and fly the plane" experience in his back pocket, and a CA who was raised in the ab-initio system of memory items>qrc>qrh troubleshooting discipline. Oh yea, this could all be just showing up right at clean up altitude, so fairly low to the ground while you're already busy flying.
 

wink

War Hoover NFO.
None
Super Moderator
Contributor
Setting aside legitimate criticism and observations on the type of training and experience atleast one mishap crew had that may or may not have hampered their chances of survival, MCAS uncommanded trim is runaway trim by any logical interpretation. BTW, my QRH does not specify "continuously". I don't know what the Official Boeing book says, although I was told some time ago the airline was ditching all company EPs and Abnormals for factory procedures to limit liability. So, we don't know the mishap crews training, little about their experience, and nothing about the procedure in their book or trained to. I find it hard to believe they thought of and rejected the QRH Uncommanded Stab Trim procedure because of the word "continuously". If one is to get hung up on precise words, I'd consider trim doing something independent of input as uncommanded and that is in the title of a procedure that stops the plane from killing me.
 

FrankTheTank

Professional Pot Stirrer
pilot
Trying not to arm chair quarterback these specific incidents. We can't even be sure what kind of training they got. This is hangar flying. ;)
We have had guys at my airline fly the entire return to landing with stick shaker from lift off to shut down back at the gate. They couldn't make it stop. They didn't know why it was happening. They just flew the plane. It was making power and climbing. Things like stick shaker can be very annoying and distracting. I get that. But remember, if VMC, as these poor souls were, does something like stick shaker convey accurate useful info to you when you can look out the window. Pitch/Power, anyone? You don't even need an AI if you are distrustful of instruments. You have a horizon.

For the yung'uns out there, don't ever let a plane do as it pleases (sez the guy who is bidding onto FiFi). Or as Bob Hoover said, "Fly the son of a bitch all the way into the crash."
Or like trying to fly with out altitude call outs on landings.. lol. Amazing how much I use that...

On side note, 62 hours in 6 months... #winning
 

scoolbubba

Brett327 gargles ballsacks
pilot
Contributor
Preliminary report shows the Pilots did follow Boeing's procedure but were still unable to recover.

This article discusses how, due to "excessive manual trim forces," it is possible for the 737 Max to be unrecoverable after disabling electric trim at normal airspeeds.

What a shame that everyone so quickly jumped to blaming the pilots because of the country and airline involved...

Why not wait for the technical investigation to end before using your jump-to-conclusions mat?
 
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