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Old 24th Aug 2012, 07:02
  #85 (permalink)  
HazelNuts39
 
Join Date: Jul 2009
Location: France - mostly
Age: 80
Posts: 1,689
Originally Posted by CONF iture
But what is the THS setting already when the elevators reach 5 - 6 degrees NU for the airplane to stall at the 10 deg of AoA time 02 11 00 ?
The airplane stalled at the 10 deg of AoA time 02 10 57. The THS was then at -3.5 degrees. Elevator 5 - 6 degrees should be read as equivalent elevator angle for THS = 3 degrees.

BEA quote: However, positive longitudinal static stability on an aeroplane can be useful since it allows the pilot to have a sensory return (via the position of the stick) on the situation of his aeroplane in terms of speed in relation to its point of equilibrium (trim) at constant thrust. Specifically, the approach to stall on a classic aeroplane is always associated with a more or less pronounced nose-up input. This is not the case on the A330 in alternate law. The specific consequence is that in this control law the aeroplane, placed in a configuration where the thrust is not sufficient to maintain speed on the flight path, would end up by stalling without any inputs on the sidestick. It appears that this absence of positive static stability could have contributed to the PF not identifying the approach to stall. (End of quote)

The BEA comment is correct, of course. But in the circumstances of AF447 it is mostly theory. It applies if you approach the stall slowly, in still air at low altitude gently manipulating the stick so that you can feel the stickforce increasing the closer you get to the stall. The subtle change in stickforce characteristics hardly matters to a stressed pilot who jerks the stick backwards to increase pitch from 6 to 12 degrees in a couple of seconds. I quantified the difference in terms of stick angle and force.

Still, if the guy has direct law, he may as well bring the airplane to the stall, no question, but what do you make of the following ?

THS is still at 3 deg and the stall cannot be that developed so the indicated airspeed won’t go below the threshold to silence the stall warning that will still warn when the captain is back. Of course if that captain had the chance to naturally contemplate what kind of input is made by the PF on the flight control commands … that could enormously help him to positively evaluate what’s going on here.
I agree with the first sentence, and wrote essentially the same in one of my recent posts. Regarding the captain, the stall warning is loud enough to be heard through a closed cockpit door. The captain must have heard it when he entered the cockpit.

Last edited by HazelNuts39; 24th Aug 2012 at 09:38. Reason: THS changed to 3.5 degrees based on final report fig. 63
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