tdracer
The link doesn't work, but at least on the Boeing aircraft I'm familiar with (basically everything save the 737), airspeed doesn't go NCD until 30 knots.
Interesting - it raises the thought that when considering the range of system reliability the airframe manufacturer must use the limits defined in the equipment manufacturer's Declaration of Design Performance (DDP) not values picked out of a hat. If one probe manufacturer says OK above 30 kts and another above 60 kts then those numbers will be what the airframer will use. Which leads to the question - does anyone know what make/model AoA probes are used on the Boeing fleet and Airbus fleet?
rudderrudderrat
Please explain why you dismiss, for the 15th time at least, a vertical descent rate of 10,000 ft per minute (about 100 kts) does not qualify as a valid speed for angle of attack vanes.
The continued stall warning, whilst they were stalled, might just have improved the Captains' SA.
Edit. Is it really that difficult to have stall warning Valid >60kts AND on ground, Or valid when airborne?
When one puts V/S and ground speed together, the aircraft never got below about 150 kts throughout the whole process. That means the AoA probes as probes were working properly and supplying valid signals (as long as the AoA did not go out of the probe range). As has been explained many times, the problem was that the extremely high AoA took the aircraft right out of any sensible AoA range for which the PEC algorithms might have been defined. Consequently the measured airspeed was wildly different from the actual airspeed and fell to below 60 kts IAS. That, taken with the probe manufacturer's DDP was the reason for the AoA signals to be declared non valid.
I agree that a continued stall warning might have made a difference. I have said it before, but I will repeat it, the aircraft was designed to meet JAR 25 Change 13, which says:
Stall warning must continue throughout the demonstration, until the angle of attack is reduced to approximately that at which stall warning is initiated.
and for the demonstration
As soon as the aeroplane is stalled, recover by normal recovery techniques
This differs from the latest rules (CS 25)
Once initiated, stall warning must continue until the angle of attack is reduced to approximately that at which stall warning began.
Clearly, it was not intended (and is not intended) that the stall demonstration should be taken too far into the stall, so there was no requirement to maintain stall warning through a prolonged stall. If present rules are interpreted as requiring a valid signal that angle of attack has been reduced to below stall warning then this would IMO cover the AF447 situation.
As for "Is it really that difficult to have stall warning Valid >60kts AND on ground" I can only say that it would be a futile exercise as it is virtually impossible to stall an aircraft with the wheels on the ground since it would be attitude limited well below any stall AoA.
Dozy
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.
I covered your first point above. The 'flipping' of the AoA signal on the DFDR is I think caused by the AoA going above the range of the instrumenation (50 deg plus!!!)
No - the first panel was convened by the SNPL using the families' group as a cover (and the report contains several glaring errors). Airbus probably don't have an opinion either way.
I agree with jcjeant - the experts panel was convened by the French judiciary, and in fact this is said explicitly in the preamble to the French original.