The pilots in front when the speed disappeared and AP tripped had no proper understanding of alternate law and of course no clue to unreliable speed procedure. In alternate2 law flight path is maintained. Only wings level were required to be ensured. When you are caught in a situation to which you have no clue then the fear factor can come in and then action taken have no logic or rationale. Pilot was thinking of climbing all the time before it happened so that was in his subconscious and unreliable airspeed after takeoff has TOGA 15. So the bizarre actions appear to be combination of the two. Stall warning comes from AoA not speed but AoA probe is an aerofoil which requires certain dynamic pressure to stay afloat to measure and below certain speed 60kts in this case it may have just flopped was unable to register anything and was taken as non computed Data and rejected for stall warning. It may not have been designed so but it may be functional reality of the system. Has the crew just held the status quo for a minute the accident wouldn't have happened because the speed came back but by then they had put the aircraft in a region where not even test pilots go.
Anyway it's too late to discuss unreliable speed as Airbus now has mathematically calculated airspeed which they call it digital back up speed. This doesn't require any anemometric input. This supervises the ADR calculations and in case of all ADRs going rogues their speed indications are replaced by the Digital Backup Speed. A350 does it automatically A320 does it through ECAM actions.
Last edited by vilas; 27th Mar 2023 at 09:32.