Originally Posted by
jcjeant
Hi,
How it's possible that the horizontal stabilizer stay in climb position when the PF perform a dive command ?
Don't know yet - very likely will be part of the detailed technical investigation.
Some possibilities (from my basic understanding of the engineering)
a) because auto-trim has been lost, it's not there in all laws (not clear this is what happened in this case)
or
b) because autotrim went wrong - possibly due to invalid speed input to gain
or
c) because maybe the pitch-down input was brief and/or could be satisfied without moving THS
Remember the pilots went hard pitch up (to the "stops"), then briefly pitch-down, quite possibly the attitude never reached level let alone "dive". BEA states that "angle of attack decreased" following the pitch-down - therefore the it appears the a/c was still responding to pitch controls (and in the right direction, but at what rate?). Shortly after, the pilots comment about reaching FL100, and there are further control inputs - not specified, but possibly pitch up again...
Another consideration:
BEA: "The airplane was subject to roll oscillations that sometimes
reached 40 degrees."
From
http://www.airbusdriver.net/airbus_fltlaws.htm:
No requirement to change pitch trim for changes in airspeed, configuration, or bank up to 33 degrees.
Not clear what those two taken together mean - maybe autotrim stopped temporaily due to the roll angles.
Note: there is still insufficient information to say the aircraft and flight control systems are in the clear, but equally not enough to show they are to blame. We do know, however, that the aircraft didn't pitch-up and stall on its own - pilot inputs were made. I'll leave those to the heavy pilots to discuss.