DozyWannabe

As far as I'm aware it's not a technical limitation of having AD and IR computation in the same unit, so much as a design decision to supply only verified good data to the crew if at all possible.

What we have to bear in mind at all times here is that the situation the aircraft ended up in was completely off the beaten track in terms of the flight envelope - using the FPV to aid recovery from a stall following UAS was probably considered a very improbable edge case when the system was specified.

Remember that one of the AoA vanes in this case was in fact frozen and providing bad data too (and in fact was out of action for longer than the pitot tubes).

The new BUSS system is intended to use other data sources to provide airspeed data, among other things, but it was not fitted to this aircraft.