Abstract. An adaptive compensation observer is presented for fast diagnose of multi-effectors aircraft in the presence of control surfaces fault, which directly estimates the deflection angles of control surfaces. An augmented observer is designed for the estimation of system input, and an adaptive compensation is introduced to improve the dynamic tracking performance of observer. Simulation results suggest that, for different cases of actuator faults, the proposed observer methods can achieve fault alarm within 20 milliseconds and determine the fault location in 0.22 seconds.