Oscillatory Failure Detection in the Flight Control System of a Civil Aircraft Using Soft Sensors

This chapter aims to detect oscillatory failures affecting a flight control surface (FCS) –specifically an aileron– of an aircraft. It presents the principle of supervision and the design of a soft sensor for the oscillatory failure case detection. The chosen principle for diagnosis is based on testing the adequacy of available measures in a control system (CS) servo-loop toward its model. Two kinds of failures must be detected, which are identified as “liquid failure” and “solid failure” as a disturbing signal is superimposed on or replaces the control signal. The chapter tackles the problem of fault detection and isolation (FDI) by the test of standard deviation. This problem is treated by a correlation test between several residuals. The quantitative analysis of residues (rb(t), rs(t) and rl(t)) confirms visual study and shows how the recognition is automatically processed from a numerical point of view.