HazelNuts39,
I am rather wondering what the performance of BUSS might be in "unusual attitudes". It is intuitively obvious to me that if the plane can be expected to stay flying "normally" on pitch and power one could work backwards from altitude, pitch, and power to get an airspeed indication when the plane is more or less in a steady state. At reduced accuracy it might even be able to make good guesses while altitude is varying. What's not obvious is what could have been derived from the plane's movements and power settings once the upset had begun. At that time the velocity vector becomes more interesting than mere speed.
BUSS would be good for getting through an upset period if you don't do anything stupid.