Fault diagnosis and fault-tolerant control techniques for aircraft systems

This chapter analyses and discusses an active fault-tolerant control (FTC) system for avionic applications. The approach applies to an aircraft longitudinal autopilot in the presence of faults affecting the system actuators. The key point of the developed FTC scheme consists of its active feature, since the fault diagnosis module provides a robust and reliable estimation of the fault signals, which are thus compensated. The design technique, relying on a nonlinear geometric approach (NLGA), i.e. a differential geometry tool, allows one to achieve adaptive filters (AFs), which provides both disturbance-decoupled fault estimates and fault isolation features. The chapter also shows how these fault estimates are thus exploited for control accommodation. In particular, by means of this NLGA, it is possible to obtain fault reconstructions decoupled from the wind components of the considered aircraft application. It is shown how this solution provides very good robustness characteristics and performances to the overall system. Finally, the effectiveness of the considered scheme is analysed by means of a high fidelity flight simulator, in different conditions and in the presence of actuator faults, turbulence, measurement noise and modelling errors.