Quote:
Apparently the designers decided a stall warning that would
never work below 60KTS was better than one that would
sometimes fail below that speed.
Originally Posted by Dozy
I don't think the designers made a conscious decision in that regard - it's so far outside the flight envelope that it probably wasn't considered at the time.
Dozy, I'll agree with that statement, however the whole loss of stall warning below 60 knots was a conceptual design error.
Airspeed and AOA are each
independent measures of aircraft performance. To force AOA to become dependent on airspeed is an error.
If you will recall, I ran some experiments on a surplus airline type AOA vane sensor, and the thing came alive below 20 mph.
There is no reason to suspect that there was inadequate dynamic pressure to activate the vanes on AF447, nor is there reason to suspect that the location of the sensors while at that high AOA would subject them to flow reversal or turbulence. The worst that could happen would be that the AOA would exceed the range of the sensor, but at least they would be at the limit in the proper direction.
This shut down of the stall warning system was not without consequence. It deprived the captain of an essential piece of information when he attempted to size up the situation upon arrival back on the flight deck (Remember? Stall warning shut down almost co-incident with his arrival on the flight deck).
The question I have now is, has the conceptual design error been quietly corrected?