At 12:45 AM 15/05/2013, you wrote:
We all know that pitch angle (angle of attack), and stall are
intimately related.
Massive fail.
Pitch angle and angle of attack are NOT the same thing at all.
Pitch angle is the direction the aircraft is POINTING - the attitude
indicator will show this. Subtract the angle of attack and you have
where it is GOING.*
In the case of AF447 the pitch angle was about 10 to 12 degrees nose
up and the Angle of Attack was something like 40 degrees. Deep in the
stall. Hence the steep downward flightpath.
I gather AoA is not routinely displayed on the instruments in the
A330 but can be shown.
There's another nasty Airbus trap - auto trim. After holding a pitch
command for a while the leading edge of the horizontal stabiliser
moves nose down to trim the aircraft. In this case it went to the
limit. What happens then is that moving the stick forward doesn't
have enough authority to immediately lower the nose unless you hold
forward stick for long enough for the auto trim to work. Yes you can
use the manual trim wheel but apparently use of this is not taught in
training and/or discouraged.
Another case where knowing the details of how things work and knowing
the possible traps is a good idea, instead of just teaching "operation".
* This is very obvious if you've ever flown with a Head Up Display
where the pointing direction is fixed on the HUD and also a little
symbol called the velocity vector which is the direction the aircraft
is travelling in. As the angle of attack increases(usually because
you are commanding it to do so) the v.v heads for the bottom of the
display. I had half an hour in the F/A18 sim and before that about
20+ years ago had a computer flight sim called MiG 29, written by
people who worked on real flight simulators at British Aerospace.
Very obvious in both of those.
Also was very obvious on my first flight down the Avon Valley at low
altitude at 240 knots. As the pilot banked the aircraft and pulled to
go around the contours I could see the difference between the
direction we were travelling and the direction we were
pointing momentarily as G was applied.
Mike
So if the aircraft was stalled at 38,000' or so, this onboard
instrument would be indicating the fact, and the pilot should have
reacted and taken the appropriate (quite routine), action to
correct the situation.
I would be interested to know the height loss figures for recovery
from a straight ahead stall for this aircraft. Can anybody provide
this information?
Gary
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