Angle of attack is determined by comparing aircraft pitch to the actual flight path angle through the air. This is equivalent to the angle at which the wing is intercepting the body of air surrounding the aircraft – exactly the same as a probe based AoA system. Pitch is determined by a precision internal AHRS, and flight path angle is determined by a precision ADC (airspeed and vertical speed). The resulting angle is then augmented with G-Load, as determined by internal acceleration sensors.
For example, during a climb, if the pitch angle is 10 degrees up, and the aircrafts flight path through the air (forward airspeed and vertical speed) is also 10 degrees up, the equivalent AoA is 0 Degrees. However, if the flight path angle through the air is only 7 degrees, then the equivalent AoA is positive 3 degrees as the wing is no longer able to maintain full lift.
Therefore, no dedicated AoA probe is required – only internal inertial and pressure sensors (8 in total). Connection to the aircraft’s pitot static system is required.
Reference Sperry Patent #3,948,096 for additional implementation details.