View Single Post
Old 5th Aug 2011, 13:53
  #1598 (permalink)  
Join Date: Jul 2011
Location: Northern Hemisphere
Posts: 195
Certainly this is material for reflection, and better understanding of the moments before, and when all of it started.....

Here is a set of graphs, that may help visualize certain parameters at the moments before the AP disconnect, and passing from Normal Law to Alternate Law - this is the moment of the AP and A/THR disconnects.

A red vertical line marks the moment of the Normal to Alternate Law change.

I notice a Pitch Nose Down, right before the Law change.
I can also see now, that the slight Altitude loss (if the BEA graph is accurate) was right after the Law change. At the time of the previous post, I thought it is before the Law change

One can visualize the increased degree of turbulence based on the areas marked on the 3 graphs of acceleration right before the Law change. There is an increase in up-down-left-right-forward-backward motion. The Vertical Speed around that time also show and increase, and decrease - reflecting the Vertical Acceleration changes.

Very important point. So...

AP disconnects
a/c at 0 deg pitch => will descend
pilot stick back 3/4 causing nose up pitch 11 deg.
climb rate goes up.
after 4 seconds first stall warning
after 15 seconds altitude has not changed (downdraft/reduced thrust?)

So PF was correct to stick back but he over does it.
Stall alarm sounds, he eases off on the stick pushes it fwd briefly, alarm stops.
Then he resumes stick back to maintain altitude.
Now the THS starts helping PF to pitch nose up.
Now he is gaining altitude with help from THS.

Report #3, Page 111, Longitudinal parameters

Notice the insidious influence the auto THS (cyan) has on elevator position. At some points he is stick forwards (red line, 02:12:17) yet elevators stay around -30 deg (purple). Clearly this would add to the confusion of inputs.

Last edited by airtren; 5th Aug 2011 at 16:06.
airtren is offline