Feasibility Study of a PHM System for Electro-hydraulic Servo-actuators for Primary Flight Controls

Electro-Hydraulic Servo-Actuators (EHSA) are by far the mostly used type of actuators in aircraft primary flight control systems. Though electrical actuation is been considered since long as a possible replacement of hydraulic actuation for aircraft systems, EHSAs are still the technology of choice in the primary flight control systems of new commercial aircrafts. Considering that 10 or more EHSAs are typically used in an aircraft flight control system, the development of an effective PHM system for this equipment could provide large benefits and be of great interest for the OEMs and for the air fleet operators. This paper presents the results of a feasibility study making up the first part of an ongoing research activity focused on the development of a PHM system for EHSAs used in fly-by-wire primary flight control systems and takes as a use case the primary flight control actuator of a wide body commercial aircraft. One of the key features of the research is the implementation of a PHM system without the addition of new sensors, taking advantage of the available signals. This offers the possibility of implementation of the PHM system on the existing platforms and not only as a proposition for new aircrafts designed with a complement of additional sensors. The enabling technologies for this PHM system borrow from the area of Bayesian estimation theory and specifically particle filtering and the information acquired from EHSA in-flight and during pre-flight check is processed by appropriate algorithms in order to obtain relevant features, detect the degradation and estimate the Remaining Useful Life (RUL). The results are evaluated through appropriate metrics in order to assess the performance and effectiveness of the implemented PHM. This paper describes the methodology of the feasibility study, which shows how the novel PHM technologies proposed for a PHM system for the EHSAs of primary flight control actuators can allow the migration from unscheduled / on-condition maintenance to condition based maintenance targeting the perceived objectives of the OEM and of the aircraft operator.