Originally Posted by
YYZjim
Dear Alchad:
The two traces of interest in the chart are the red one labelled CCForce_PitchCWSLocalFDR() and the green one labelled CCForce_PitchCWSForeignFDR(). As I understand it, the "local" one is for the left-side column; the "foreign" one is for the right-side column. These traces record the forces the pilots are applying when they push or pull on the yoke. The two yokes are tied together through a break-out mechanism. If only one pilot pushes or pulls, the break-out mechanism will cause his side's FDR trace to be very slightly greater than the other pilot's. Of course, the traces will diverge if the two pilots are both at work, but pushing or pulling in different directions or to different degrees. However, the two traces will also diverge if the differential input from the two pilots is so great that the break-out mechanism fails, something like an electrical fuse. After break-out, each yoke has independent control over the elevator on its side of the airplane.
Perhaps I should clarify my use of the word "failure". The break-out mechanism may have done what it was supposed to do -- break.
My knowledge about this issue comes directly from the Leeham News report November 28, 2018, just a couple of days after the preliminary report on the Lion Air crash was published. The second and third-to-last pages of Leeham's report describe this issue in some detail.
What wonkazoo and yoko1 are debating is whether the SIC, who took control at about this time, was somehow at greater fault than the PIC, who arguably had the airplane under control up until that point. A lot seems to have happened in the ten or fifteen seconds immediately before the airplane began its fatal plunge.
YYZjim
Interesting article, but in months of following these events, this is the only time I have seen the suggestion there was a control problem other than AND trim by MCAS. I think more news would have followed if this story was correct.