Prognostic and Health Management System for Fly-by-wire Electro-hydraulic Servo Actuators for Detection and Tracking of Actuator Faults

Maintenance of flight control actuation systems is currently performed on a scheduled basis, however air fleet operators and component manufacturers are willing to move from scheduled maintenance to Condition Based Maintenance (CBM) in order to reduce maintenance costs and improve aircraft dispatchability. Prognostics and Health Management (PHM) systems are a critical part of CBM and are perceived as a breakthrough technology to effectively respond to an urgent and critical need to improve the readiness, availability, reliability, safety and maintainability of aerospace vehicles. This paper presents the results of an ongoing research activity focused on the development of a PHM system for fly-by-wire Electro-Hydraulic Servo Actuators (EHSA) without adding new sensors. The PHM system is being developed with the objective of detecting the most common faults, according to a failure mode effects and criticality analysis (FMECA). The paper describes in particular the tools used for detection and tracking of internal leakage faults of the hydraulic actuator, which is one of the most common faults of hydraulic servo-actuators in service, and for predicting its remaining useful life (RUL). The research work has been supported by the development of a nonlinear model for a reference EHSA, that has been implemented using physical equations and system parameters, taking into account environmental condition and disturbances. The model was validated through tests runs on a flight control actuator of a civil aircraft. Simulations are performed in nominal conditions and with progressive injection of degradation to verify the PHM algorithm. The performances of the PHM algorithms are evaluated by means of proper metrics.