6. Active Fault-Tolerant Control Strategy of Large Civil Aircraft Under Elevator Failures

Aircraft longitudinal control is the most important actuation system and its failures would lead to cata-strophic accident of aircraft. This chapter proposes an active fault-tolerant control (AFTC) strategy for civil aircraft with different numbers of failed elevators. To enhance the performance of the fault-tolerant flight control system and effectively utilize the control surface, a trimmable horizontal stabilizer (THS) is considered to generate extra pitch moment. A suitable switching mechanism with a performance improvement coefficient is proposed to determine when it is worthwhile to utilize the THS. Furthermore, the AFTC strategy is detailed using model following techniques and the proposed THS switching mechanism. A basic fault-tolerant controller is designed to ensure the stability of the longitudinal control system and acceptable performance degradation under partial elevator failure. The proposed AFTC is applied to a Boeing 747–200 numerical model, and simulation results validate the effectiveness of the proposed AFTC approach.