Originally Posted by
MurphyWasRight
It has pretty well been established on this thread that pilot electric trim will work in all conditions (does not stall under load) and interrupts MCAS if active as shown by ET trace at ~05:40:27. This pilot trim input was possibly then interrupted by cutout switches.
Other than 'deer in headlights' loosing it I see a few possible factors:
1: Pilot accustomed to short blips not comprehending amount truly needed, this fits Lion Air when the FO was ineffective at the end when PIC handed over control while the Captain was mostly successful.
2: Trimming by column feel not position: May seem that AC is closer to trimmed than it is. In other words if you have been pulling really hard then just slightly hard may feel like close to trimmed, I am sure the pilot did not want to over trim given all the alarms.
This might explain ET first retrim at 05:4-:15. Unfortunately we don't have the column force graph, just position.
3: Some as yet to be revealed flaw that interferes with pilot trim inputs; one possibility is biomechanical factors related to actuation switches after prolonged pulling.
This is unlikely but could explain the final seconds of both accidents.
Hopefully the final reports will fully address this question.
Another factor is that given the dependence on automation these pilots may have never trimmed this aircraft or any others in their airline career.
Consider that if the airline policy was to use the autopilot to the max (sorry about the pun), their entire career of flying a Boeing product would be to takeoff, climb to 400 ft then engage the autopilot. For this short bit of flying there is no requirement to trim if the stabilizer trim was set properly. During any changes in speed or configuration the autopilot would automatically trim the aircraft. The aircraft would stay on autopilot until short final (1000 AGL or less), the autopilot would be disconnected and, assuming that no configuration or speed changes occur, the aircraft would not have to be manually trimmed.
In speaking with friends flying outside of “the western world” this is exactly what happens. In fact, if the flight data analysis (which, in some cases is analyzed after every flight at some carriers) shows manual flying, the Captain gets queried about why. If it happens too often they get docked pay.
To those of us that insist on doing some hand flying of our jets, this might seem preposterous however that is what is going on in many parts of the world.
I would be interested in hearing if others are under this practice or have colleagues that are.