Originally Posted by
rudderrudderrat
Edit. Is it really that difficult to have stall warning Valid >60kts AND on ground, Or valid when airborne?
When you have AoA vanes that are only certified to operate at >=60kts IAS, and the unavoidable fact that Stall Warning is a function of AoA - absolutely!
Regarding your point about the airflow from the VS in the stall - I don't know. You'd need a proper aero engineer to be certain, but I'd say there would be too many variables involved to allow for considering readings in that scenario as accurate. Certainly the DFDR output from the AoA vanes once the stall is established seems to degenerate very quickly into flipping between extremes - and to my mind would only cause more confusion.
@tdracer - we're not talking about IAS going NCD, we're talking about AoA vanes that are only certified to operate reliably above 60kts IAS.
Machinbird's F4 would have had the wind over the deck plus the airspeed generated by the motion of the ship - a very different (and somewhat simpler) design problem to solve. An F4 is a fighter, and the AoA systems specification would by the very nature of difference in application be a very different kettle of fish. Machinbird - your AoA vanes may have been "live", but with all due respect I doubt you paid a significant amount of attention to how reliable the readings were in that scenario - and I think you'd have been far too sensible to try and test the theory by stalling your F4 to the extent that your pitot tubes were being fouled and registering IAS below 60kts!
@vilas:
It is very clear that the pilots in the cockpit simply had no idea of stall phenominon and unreliable speed technique.
I have a very tough time believing that a highly-qualified sailplane/glider pilot* (such as PF FO Bonin) would have been completely clueless about stall - which is why I've long maintained that he had some kind of psychological shock response which threw him sufficiently to get muddled. PNF FO Robert tries to correct him verbally several times regarding his pitch attitude ("you're going up, so go down") during the initial zoom climb, but as the aircraft moves into the stall regime and more of the instrument readings stop "making sense" he seems to lose his earlier confidence - which was undoubtedly a tragic shame.
We've been through this countless times before and no consensus was reached - in part because many posters are wedded to their own notions of what the real problems were here, but one thing that needs to be remembered above all was that
the Stall Warning functioned correctly for at least around a minute before the aircraft went too far out of the flight envelope, and it was apparently completely disregarded**. For those that want to compare brand A with brand B, one only has to look at the Birgenair 301 B757 crash, where the Captain disregarded the stick shaker in favour of the first (erroneous) warning he got, which was overspeed.
* - EDIT - I'm not saying 'no pilot would...' here, I'm saying that in order to fly a sailplane/glider to a high degree of competency one has to have a very thorough appreciation of the mechanics of flight, because in a glider there is no TOGA detent or switch - approaching stall one has no option but to trade altitude for airspeed!
** - EDIT 2 - The point I'm trying to reinforce here is that while the Stall Warning was silenced at approximately the same time the Captain returned, it sounded correctly and continuously for long enough that the two FOs should have at least acknowledged it. And there were enough secondary indications (unstable pitch, dubious airspeed, rapidly unwinding altimeter) that a Captain should have been able to use to diagnose a stall.