A enlarged image of the DFDR trace is
here
MM43, thank you for that beautiful readable DFDR trace. Much better than the fuzzy one in the online accident report!!
The A319 is the baby brother of the A330. Much smaller but with a strong family resemblance. As such, many of the design concepts that went into the A320 family are reflected in the A330, but executed or packaged in slightly different ways. If the A319 is showing signs of control rate limiting, then it is likely that the A330 can do the same.
With this in mind, I would like to call attention to some anomalous indications in the DFDR trace.
First, look at the position of the R & L elevators. Wouldn't you expect both elevators to be moving synchronously? But just before 14:48:10, the L elevator (brown trace) follows a stick pulse, but the R elevator (blue trace) does not. Then at 14:48:12, the R elevator responds to a stick input, but the L elevator does not. This split behavior continues until 14:48:17 at which point the aircraft has apparently flown out of the turbulence and is in a recovery phase.
Now look at the blue and magenta traces in the middle of the graphic. This is rudder position(magenta) and rudder pedal position(blue). Wouldn't you expect the two to be nearly synchronized with a slight lag for the hydraulics to catch up with the pedals? But at 14:48:06, before the autopilot is switched off, we are beginning to see the rudder lagging the pedals. (I don't wish to get into a discussion about whether he should have been on the pedals in the first place, just how well the aircraft followed the pilots commands.) By 14:48:15, the rudder acts as if it has a mind of its own and is doing other than what the pedals commanded. Finally by 14:48:23, the rudder starts to follow the rudder pedals (coincident with the aileron trace quieting down).
There are other indications in the aileron traces themselves. Yes the right and left ailerons mirror each other fairly well, but they are lagging the control input by almost a second and the position traces are becoming triangular in shape.
To me, these events in the trace may be the results of hydraulic supply rate limiting, but I realize that yaw damper inputs can superimpose on the pilots rudder inputs. Others on this forum have no doubt seen such DFDR traces before and may have better insight as to the cause, but I am concerned that the hydraulic demand from continually moving ailerons and spoilers could cause a control problem in very turbulent conditions on Airbus aircraft.
And if I am definitely barking up the wrong tree, please set me straight.