Inertial Angle of Attack estimation for a small transport aircraft

In this work, warning flights of a small commuter aircraft are analyzed. One of the reasons for warning to occur in Stall Warning System (SWS) is due to difference in Alpha/ Angle of Attack (AOA) values computed using two methods exceeds ± 5°. In the first method, vane sensors are used to acquire local alpha and get freestream AOA using airdata calibration tables. Whereas, inertial alpha is computed using inertial sensor measurements from Attitude and Heading Reference Unit (AHRS) and Air Data Computer Unit (ADCU). The flights that are investigated in this work are those where, the alerts happened because of this reason. Cause for the discrepancy is clearly presented. Solution to the problem has been proposed using recursive filtering technique. An Extended Kalman Filter (EKF) based flight path reconstruction technique (FPR) is used to estimate true AOA and inertial AOA. Flight data is analyzed offline and results are presented for the same