@BOAC
Firstly let me say that I am NOT arguing that the A330 design does not need any change - on the contrary I think the stall warning logic should be altered. However the discussion relating to validity or otherwise of the AoA signal does, I think, ignore some relevant facts:
Your point about 'trigonometry' is irrelevant when we were talking AoA signals and is only relevant in terms of IAS which only enters the fray due to some software code. Therefore it would not matter if the jet was flying backwards or upside down - an airflow of that magnitude would, I suggest, generate a 'useable' AoA signal. Whether the designers choose to ignore that signal is another matter. That was one of the errors of design.
I doubt very much whether usable AoA signals would be generated if the aircraft were flying backwards or upside down, but I imagine you wrote that tongue in cheek ...
More to the point, if an equipment manufacturer declares in his formal paperwork that his equipment will work to specification only inside a given range of ambient parameters then the aircraft designer has no option but to conform to those limits. It is not a case of design error but one of a fully auditable certification trail.
The problem comes of course when the system sees input conditions which say that the operating limits of the equipment have been transgressed, but the measurement of those ambient parameters is itself false. To that extent Chris Scott's comment on trigonometry is relevant - the input data, in this case airspeed, was rendered false by the angle at which the airflow entered the pitots. Was it then a design error to fail to consider this case?
- not sure what 'vent' means here, but it does appear that the designers forgot this very important 'trigonometry' and that a jet in a fully developed stall can and did, in fact ?'vent'? below 60kts (IAS).
I doubt very much that the designers "forgot" that an AoA in excess of 40 deg would give stupid speed signals, but they did of course fail to believe that a trained pilot would allow the aircraft to get into that state. Be fair, would you have believed it before publication of the AF447 final report? In which regard I would refer you an earlier posting, from PJ2 I think, that designers work on an assumption that the aircraft will be flown to a given set of rules, allowing for some sensible variations thereto, but not to any extreme one cares to dream up.
So what of their treatment of the stall warning which is, when you go back to basics, the reason for all this discussion?
With hindsight the logic is faulty, but I don't see any need to alter the logic governing validity of AoA signals which might well bring on other problems we know nothing of. Instead I would propose a change of stall warning logic so that if triggered by a valid AoA signal it should stay latched on until it received another valid AoA signal that stall conditions were a thing of the past. That would have avoided the confusion found in the AF447 cockpit for a minimal change to the aircraft systems. It would also, incidentally, bring the aircraft into line with the latest EASA requirements on the subject.