Originally Posted by
wheelsright
"No evidence" is a commonly used phrase used to justify all manner of absurdity (usually by politicians). The absence of evidence does not rule in or rule out anything.
"It is absolutely clear from the data (both ET302, and both LA610 flights) that the pilot actuated stab trim stopped and reversed the MCAS trim input every time it was used. As powerful as MCAS was, it could not overcome the strength inherent in the Captain's left thumb" It is not absolutely clear at all. The FDR does not track the thumbswitch position as far as I know. Thus, it cannot be said with certainty that there were not additional electric trim up inputs that had no effect. Your assumption seems to be based on the accuracy of Boeings publications. I do not think that any pilot, even a very bad pilot, would not make further electric trim up corrections under the circumstances. For these reasons there remain doubts in my mind. In the case of ET302 it seems the crew reactivated electric trim in desperation... following that action it is difficult to believe that they did not do so to apply constant electric trim up via the thumb switch. It is a puzzle what actually happened, but unless you KNOW what the pilots ACTUALLY did it is mere speculation rather than being "absolutely clear".
The DFDR traces show not only pilot and automation inputs on separate tracks, they also show whether the stab moved in response. There is even one example where MCAS is shown trying to make an input but the stab does not move because the stab trim switches were in the cutout position. Otherwise, every time that either the pilot or the automation made a stab trim input, then the stab moved as one would expect. I do not know whether the DFDR picks up the pilot trim signal directly from the switch or from somewhere else, but there were plenty of pilot inputs that corresponded to a stab movement. To conclude that the yoke trim switch suddenly stopped working requires a much greater leap of faith than a conclusion that it was used ineffectually.