Originally Posted by
RobertS975
As stated previously, the stall warning system shuts down below a certain IAS... cannot recall exactly, but 80kts or so.
The AoA vanes are only certified to produce valid information above
60kts IAS. As I said earlier:
Originally Posted by
DozyWannabe
No Computed Data - i.e. the value is invalid and cannot be used for further processing.
That was a secondary consequence (or "side effect" in engineering-speak) of the systems design as a whole. The SW ceased because it was no longer receiving valid data from upstream - there was no design intent to "shut off" the SW directly.
...
We've been over this many times in earlier threads, and the fact is that if you latch stall warning for one scenario, it runs the risk of giving false information in several other scenarios. It's a very difficult system to make completely failsafe across the board - and as I repeated above, the silence from other airframers does tend to suggest that their systems would have behaved in a similar manner.
...They then reasoned that whatever they had just done put them into a stall, and reversed their control inputs to make the situation worse.
I also stated in that post that a bit of thought on that point should have indicated a problem with the SW system rather than the ND input causing a stall, because lowering the nose reduces AoA, and basic aerodynamic knowledge (which pilots should have) of the facts states that it is effectively impossible to go from an unstalled state to a stalled state by reducing AoA.
Put in more basic terms, there is no way that lowering the nose (and reducing AoA) should stall the aircraft. It may have added to the confusion, but I'd be surprised if they thought they'd put the aircraft in a stall by commanding Nose-Down.
If we're going to speculate on the AirAsia front, I reckon this thread should go a bit quieter now...