Originally Posted by
BOAC
I am going to need a rewind here again, I'm afraid:
a) References appearing to the Airbus 'stall recovery pull-up' manouevre. Is this right?
Don't think so. Two things could confuse with that though.
One is the AB GPWS escape procedure - namely pull the stick back to the stops and alpha-prot plus alpha-floor will automatically give you climb performance (without risk of stall) that you would need a sky god to get on a conventional a/c. Nowt to do with stall recovery or 447 though.
Second is the practice noted by BEA and others before of emphasising minimum altitude loss in (approach-to) stall recovery, and perhaps teaching stall as a speed problem not an AOA problem. That is an industry problem though, not an AB problem.
b) References to the fact that the stall warning 'cannot' sound in Normal Law. Is this right?
Arguable. Stall warning
can trigger in normal law, but I believe the immediate effect will be a law degradation. In normal law the system thinks it is keeping within the envelope, plus a margin, so this is a "should not happen". If it does happen, the system is going to drop envelope protections because it is clear the envelope simply isn't where it was thought to be...
I suspect that it is true to say the by the time you hear the stall warning you are not in normal law...
EDIT: disregard the bit above, it's memory playing tricks (i.e. it's b***ocks). I sit corrected.
c) References to situations where alpha floor protection in some species of Alt Law might be absent. Is this right?
Alpha floor is an autothrust function, not sure it is really a "protection". It will add thrust as AOA rises, to give you more performance, but in the absence of alpha protection (which will put the nose down to keep AOA in bounds) it cannot protect you from stall. TOGA alone does not prevent you stalling, as 447 shows.
Alpha floor is, as far as I know,
not active in any law outside Normal [maybe on some AB type - but I don't think so].
Putting these together, this means, does it not, that it is considered 'correct' to pull up as hard as you like at the 'stall' in Alt Law where you might have no stall protection? I am just not understanding why the logic of all the years of aviation is suddenly overturned. I do hope I have got this wrong.
If you were right, I think we'd already have a dozen or more AB on the ocean floor as a result.
Something, however, made this crew think it was correct to pull (and Colgan and Ethiopian and many others further back)...