Airbus A350 operators are being instructed to check the performance of electro-hydrostatic actuators for the type's primary flight-control surfaces.
The European Aviation Safety Agency says that some of the actuators, manufactured by Moog, have been found to suffer from degradation as a result of moisture admission.
Consequent weakened insulation resistance in the direct drive solenoid valve, it says, could prevent its being able to command or maintain the actuator in active mode, reducing control of the aircraft.
The similarity of design means all five of the primary flight-control locations – inboard ailerons, elevators and rudder – could be affected.
EASA says the problem has been traced to incorrect sealing. Moog has improved its manufacturing process to ensure adequate sealing and issued a service bulletin. Airbus has also published instructions to restore performance of the actuators.
Operators of A350-900s and -1000s are being ordered to carry out an insulation check of the solenoid valves on each affected actuator, and take action – including possible actuator replacement – depending on the measurement.