JD-EE, re yr #460 -
From Joelle Barthe's text:
This (the BUSS - HN39) indication is based on angle of attack (AOA) sensor information, and is therefore not affected by erroneous pressure measumements.
Leaving out the more subtle details for readability, this is how I think it works in principle:
If one knows the airplane's aerodynamic characteristics (in particular, lift coefficient versus AoA), and the airplane's mass and airspeed, one can calculate the normal load factor for each AoA. I think the BUSS essentially uses the same equation in reverse, solving for airspeed from sensed LF and AoA.
P.S. For two reasons this doesn't work very well at high altitude. Firstly, the slope of AoA vs airspeed becomes rather shallow at high airspeed. Secondly, the aerodynamic characteristics vary with Mach number, i.e. (pressure) altitude.