Originally Posted by
737mgm
Stick shaker only on one side, several caution lights going on, differing airspeed indications create a very confusing situation. For exactly that reason there are memory items in order to deal with that situation and they must be carried out.
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There was not one procedure done wrong but several done wrong. Each one of these procedures would have saved the aircraft. Carrying out the unreliable airspeed memory items is one procedure
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Things are never as black and white as one might wish. The ET pilots were not at all perfect but they were also misserved by the system.
This is text from a Boeing UAS flow chart someone posted a while back, not I do not have access to current procedures,although what probably matters as much is what was in effect when the Pilot was trained.
Seems totally reasonable to decide it is false AoA related warning.
AoA sensor failure on Takeoff
If AoA sensor is failed high,stick shaker on failed side will activate on rotation accompanied by IAS/ALT disagree warning flags.
If the pitch power and config are consistent with takeoff and the good side ASI agrees with the Standby ASI,then it is a false warning
There is a side arrow to the side that states "If in any doubt execute the UAS NNC"
The pilot with good side data becomes PF
Land immediately
With a 360 hour co-pilot there may be a reason the Captain retained control, especially with relatively small ASI difference.
Originally Posted by
737mgm
And the Ethiopian Captain did trim out the MCAS induced movement completely the second time it activated. So we could already talk a lot about why they didn't do it the whole time, then lower the flaps for landing (MCAS deactivates) and land.
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even in that case, carrying out the stab trim runaway memory items correctly once MCAS engaged (please stop these ridiculous comments that the MCAS activation cannot be recognized as a stab trim runaway) would also have saved the plane.
Note, the times below are from the FDR chart which is hard to read better than a second or so due to ambiguous sloping edges on binary traces.
The first MCAS trim started at 05:40:00 ending about 9 seconds later, this was as the autopilot dropped out after flap retraction.
The pilot only partially unwound the trim at 05:40:15, 5 seconds later the second MCAS input started but was cancelledby sustained pilot trim starting at 05:40:29.
This second trim attempt lasted until the stab trim was cutout.
From the prelim report:
At 05:40:35, the First-Officer called out “stab trim cut-out” two times. Captain agreed and First-Officer confirmed stab trim cut-out.
Given that Boeing changed the cutout switch functions on the MAX so that
either one disabled all electric trim whereas on NG the right switch disabled automatic trim only it is possible/likely that the pilot was still trying to trim.
Much later the (very sparse) partial transcript has this:
At 05:41:46, the Captain asked the First-Officer if the trim is functional. The First-Officer has replied that the trim was not working and asked if he could try it manually. The Captain told him to try. At 05:41:54, the First-Officer replied that it is not working.
This supports the idea that they believed they had only disabled automatic trim and manual electric trim should still function.
This difference is not highlighted, or mentioned at all depending on which MAX type conversion powerpoint the crew used.
Bottom line is that runaway trim nnc was executed but they were (apparently) left with an inability to crank the trim wheel.
"Unloading" maneuvers used to be part of runaway stab training but apparently were dropped some time ago.
To anyone contemplating commenting on the emergency AD stating to trim first if MCAS runway:
A: That was buried as a note -after- action items.
B: ET pilots company may have failed to update manuals.
Of course it is tragic that they did not input sustained trim after an apparent last ditch effort where they re-enabled electric trim. I still wonder if some other factor is at work here since almost exactly the same thing is seen at end of Lion Air traces.
There was less than 45 seconds from start of first MCAS trim to loosing all trim capability.
They might have done better had they not followed the runaway trim procedure.
I do totally agree on your points on the state of training and company policy that result in poor confidence in manual skills, this undoubtedly also played a significant role in this accident.
Note I see several other responses on trim failure while I wrote this, the above is one (of several) possible scenarios.