Enhancing flight control in case of total angle of attack sensor loss

To maintain nominal flight control system functionalities during fault scenarios, enhancements of the state of-practice angle of attack fault accommodation strategies are presented. The enhancements rely on combining modern fault detection and diagnosis (FDD) techniques with a robust envelope protection algorithm. The FDD system is able to detect and isolate partial or total losses of angle of attack sensors. The angle of attack is not a directly controlled variable in the flight control system, but is used to protect the aircraft from exceeding the flight envelope. To avoid the state-of-practice degradation towards an unprotected control law in case of a total angle of attack sensor loss, longitudinal protection law functionalities independent of the lost measurements are proposed. They provide satisfactory prevention of reaching difficult flight conditions and can be operated together with the nominal command and stability augmentation system. This paper discusses the protection law design in conjunction with the sensor monitoring scheme and the nominal inner loop control law. The latest results of an extensive industrial validation and verification campaign are reported.