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Old 24th Aug 2012, 01:24
  #83 (permalink)  
CONF iture
 
Join Date: Jan 2005
Location: W of 30W
Posts: 1,939
Originally Posted by HN39
It took about 5 - 6 degrees of NU elevator to stall the airplane. In direct law that would correspond to about 3 degrees (2.8 lbf) of sidestick, vs about 2 degrees (2.1 lbf) in alternate law. Do you really believe the PF would have felt the difference in his erratic movements of the sidestick?
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 ?

You may as well disregard the following BEA comment on P187 :
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.
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.

What many here like to call 'graceful degradation' had nothing of graceful during that night.
That law that trim and that sidestick concept worked against that crew that night.
To that list of course I should have added that stall warning logic.


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