fadecfault wrote:ferpe wrote:fadecfault wrote:The problem with this belief is that it would make it seem the Investigators are 1) holding back information or 2) incompetent
The reason is there are position sensors in the left and right elevators. These Elevator sensors are dual channel with one channel reporting to the Flight Data recorder. The Investigators will have seen a split if a breakout occurred and it should have been on the chart and reported.
Considering that the Leeham author didn't mention the elevator position sensors I would side with the Investigators.
Of course, the investigators and also Boeing have more information. They have 69 hours with 1790 parameters from the aircraft. We have access to 40 of those for the last hours. We lack things like pitch and roll angles among a lot of other information.
My reaction is at the same time as the counter trimming changes to short blips the pitch forces separate for the two channels for the first time during these two flights. I have since got a better schema on the pitch channel breakout mechanism, it's not a clutch, nor a no breakout or breakout mechanism.
It's here described as a progressive cam and spring-loaded roller unit which allows progressive movements between the yokes and therefore a difference in the force the force transducers register at high differences in Yoke force in the two channels. The separation can mean the two pilots both pull on the Yokes and in different directions. What's disturbing is one stays put (red = Captain i interpret it as) while the other goes significantly higher from being the follower. Then the green stays at the put level while the red goes high. When one Yoke has moved before, the other has followed in force, not now. We can explain most other traces but not this part. Strange.
At the same time the crew only counter trims for short blips, leading to full MCAS nose down trim and then they plunge. They could be in a turn and one doesn't normally trim in a turn but the separation of the traces are no explained by a turn unless the two pilots are in un-sync on the Yokes. The increased dynamic pressure to the Elevator Feel Shift Module which decides the hydraulic pressure to the Elevator Feel and Centering Unit at the elevator should be the same to both sides. It shouldn't cause the differences in forces we see IMO.
A Couple things regarding the Leeham article :
1) The Chart has Pitch force labeled as CCFORCE_PITCHCWSLOCAL_FDR and CCFORCE_PITCHCWSFOREIGN_FDR. We can not tell which CWS pitch sensor is being displayed. The captains or f/o's sensor will display as local or foreign.
This is seen in the DFCS bite as:
P CWS-LCL (LBS)
CH A CH B
P CWS-FGN (LBS).
CH A CH B
I have tested it and each sensor feeds the local and foreign data display.
2) You can't equate force with elevator position. You can pull the column full aft and have a 50lb split between the f/o and captain. This can happen when one pilot felt the aircraft wasn't responding to nose up command of the other pilot and pulled harder. The column won't move anymore but force on it will be greater. You also push and pull in opposite directions and one sensor will read negative pounds. I registered a 70lb split (-30/+40) when I pushed /pulled the columns with one hand on each. The Graph doesn't show one line in positive and one line in negative, so the authors suggestion that the pilots worked against each other is wrong.
And, if breakout had occurred, surely a position trace would have been included in the initial preliminary report.
(edit, sorry, missed part of fadecfault's response to Ferpe. Not a fan of how quotes work now. Don't scroll, miss things.)