Design of fault-tolerant control functions for a primary flight control system with electromechanical actuators

A concept for the fault-tolerant control of a primary flight control system featuring two parallel electromechanical actuators nominally operating in active-active mode is proposed. A detailed nonlinear model of the system under consideration is created to enable the design of high-level and low-level safety control functions. Three reaction sequences combining five different reactions are proposed for the mitigation of safety-critical faults. Attention is paid to the sequence assigned to those actuator faults that permit the safe continued movement of the control surface while the system operates in active-standby mode. A control concept is developed to reduce the reflected inertial loads in this mode without permanently degrading the system performance. Herewith, the load on the active actuator reaches at the most 95% of the system's limit load when both actuators operate in a highly degraded state, whereas with the original control scheme the limit load is continuously exceeded by 30%.