Air Data Sensor Fault Detection and Diagnosis with Application to Real Flight Data P. Lu * , L. Van Eykeren † , E. van Kampen ‡ , and Q.P. Chu § Delft University of Technology, Delft, 2600 GB, The Netherlands Air Data Sensor (ADS) Fault Detection and Diagnosis (FDD) is important for the safety of the aircraft. Adaptive Fading Unscented Kalman Filter (AFUKF) is able to tackle the ADS FDD using the kinematic model of the aircraft. This paper proposes a Robust Three-Step Extended Kalman Filter (RTSEKF) for the estimation of the ADS faults. The RTSEKF is extended to Robust Three-Step Unscented Kalman Filter (RTSUKF) to reduce the influence of linearization errors when coping with nonlinear systems. However, it is found that the RTSUKF is still sensitive to initial conditions. The problem is analyzed and a Modified Robust Three-Step Unscented Kalman Filter (MRTSUKF) is proposed to guarantee its performance. The performance of the AFUKF and the MRTSUKF is tested using the simulated data of a Cessna Citation II aircraft. The similarities and differences between them are also presented. Furthermore, the performance of these two approaches is validated using the real flight test data of the aircraft. The results demonstrate their ability to be applied in practice. Nomenclature A x , A y , A z = linear accelerations along the body axis, m/s 2 p, q, r = roll, pitch and yaw rate along the body axis, rad/s u a , v a , w a = air speed components along the body axis, m/s V t = true airspeed, m/s α, β = angle of attack, sideslip angle, rad f = output faults f V , f α , f β = faults in the air data sensors φ, θ, ψ = roll, pitch and yaw angles along the body axis, rad I. Introduction P resently, Fault Detection and Isolation (FDI) has an important role of achieving fault-tolerance. 1 During the past few decades, many approaches have been proposed for sensor or actuator Fault Detection and Diagnosis (FDD). 2, 3, 4 In aerospace engineering, the FDI of the sensor and actuator is also widely studied. 5, 6 For recent advances, the reader is referred to Goupil 7 and Zolghadri. 6 The Air Data Sensor (ADS) measures the dynamic pressure, airspeed, angle of attack of the aircraft and provides the pilot with an indication of velocity through the air mass. 8 The ADS are usually installed outside the aircraft fuselage and can suffer from icing or water accumulation, which may result into blockage faults. 9 These faults may * Ph.D. Student, Control and Simulation Division, Faculty of Aerospace Engineering, P.O.Box 5058; P.Lu-1@tudelft.nl, Student Member AIAA. † Ph.D. Student, Control and Simulation Division, Faculty of Aerospace Engineering, P.O.Box 5058; L.VanEykeren@tudelft.nl, Student Member AIAA. ‡ Assistant Professor, Control and Simulation Division, Faculty of Aerospace Engineering, P.O.Box 5058; E.vanKampen@tudelft.nl, Member AIAA. § Associate Professor, Control and Simulation Division, Faculty of Aerospace Engineering, P.O.Box 5058; q.p.chu@tudelft.nl, Member AIAA. 1 of 18 American Institute of Aeronautics and Astronautics