STRUCTURAL HEALTH MONITORING OF ELECTRO-MECHANICAL ACTUATORS IN AVIATION: RECENT BREAKTHROUGHS AND FURTHER CHALLENGES

Electrical actuation systems have recently been introduced in aviation pursuing the concepts of More Electric Aircraft. Instead of employing hydraulic pipelines, Electro-Mechanical Actuator (EMA) transfers the power by "wires" with a consequent improvement of the aircraft actuation performance. However, the integration of linear electromechanical actuators is promising yet challenging in safety critical systems. Within this context, this work critically reviews electromechanical actuators currently available for aerospace application, the limits for their upcoming deployment and the different solutions to achieve an on-condition maintenance to reduce any safety risk during lifetime. First of all, the typical conversion mechanism adopted so far are briefly described with emphasis on the most suited for aerospace applications. A further insight is given to failure modes of these systems, which dramatically contrast the countless inherent advantages thereof. A particular attention is given to the jamming of the driven load, which is a critical mechanical transmission failure in many applications such as primary flight controls or landing gears extension and steering. Finally, the focus is moved to possible strategies to avoid any hazard induced by this failure. In particular, any structural alteration which is prone to induce jamming can be monitored towards the establishment of a predictive maintenance. Different possibilities are available in the way to timely assess the bearing of inner EMA surfaces where screwing is enabled.