A fault tolerant flight control system for sensor and actuator faults

The purpose of the paper is to present an approach to detect, isolate and accommodate the sensor or actuator faults using bank of unknown input observers (UIO). Full order observers, reduced order observers, unknown input observers and Kalman Filter are widely used in state estimations [1]. After the estimation of states, fault detection and isolation can be provided by conducting residual analysis. Despite the existence of unknown inputs, fault detection and isolation is implemented for a very large, four-engined, cargo jet aircraft model. Sensor accommodation is realized via switching under redundant sensor existence assumption. Actuator accommodation is provided by gain scheduling. Hence, if a fault occurs in an actuator corresponding to the control surfaces, the remainder (n-1) actuators are used to avoid hazardous flight regime. Sensor or actuator faults are detected by using residuals. Sensor faults are effective on the outputs while actuator faults are effective on the state equations. Fault isolation is implemented by taking into account that each residual is sensitive to all of the other faults but one fault. Fault detection, isolation and accommodation are shown to be functional through the simulations.