AD FAA-2020-0343

The FAA is superseding Airworthiness Directive (AD) 2018-17- 05, which applied to all Airbus SAS Model A350-941 and -1041 airplanes. AD 2018-17-05 required a check of the insulation resistance of the direct drive solenoid valve (DDSOV) of each affected electro-hydrostatic actuator (EHA) and applicable corrective actions. Since the FAA issued AD 2018-17-05, it was determined that certain EHA part numbers can be modified and re- identified as specified in a European Union Aviation Safety Agency (EASA) AD, which could inadvertently remove certain part numbers from the applicability in other EHA-related ADs including AD 2018-17-05. This AD was prompted by reports of EHA units that were returned to the manufacturer with degraded insulation resistance in the DDSOV; investigation results revealed that moisture ingress, due to incorrect sealing application, had caused this degradation. This AD was also prompted by a report of a technical issue detected on EHAs installed on inboard ailerons and elevators, causing potential erroneous monitoring of those actuators. This AD requires a check of the insulation resistance of the DDSOV of each affected EHA and applicable corrective actions, and modification or replacement of certain EHAs; as specified in two EASA ADs, which are incorporated by reference. The FAA is issuing this AD to address the unsafe condition on these products.