Airworthiness Directive for A350: failures on inboard aileron EHAs.

The European Aviation Safety Agency (EASA) is giving operators of the Airbus A350 until 11/Jan to begin daily post-flight checks of the aircraft’s 2 inboard ailerons to verify that the electro-hydrostatic actuators (EHAs) that drive the roll-control surfaces are working properly.

The AD (Airworthiness Directive) issued by EASA requires repetitive post-flight checks (activation) of each inboard aileron EHA and, in case of failure, replacement of the affected EHA with a serviceable one.

 

The interim action required by the AD (Airworthiness Directive) specifies that since 28/Dec until 11/Jan and, thereafter, during each flight day, but not exceeding 2 flight cycles, it is needed to accomplish a post-flight activation procedure on each inboard aileron EHA in accordance with the instructions of Airbus AOT A27P007-15-00.

Source: Moog

If, during any EHA activation the message “F/CTL INR AILERON ELEC ACTUATOR” is triggered, before next flight, it will be mandatory to accomplish the troubleshooting procedure on the affected EHA in accordance with the instructions of Airbus AOT A27P007-15-00.

If the failure remains, before next flight, it will be needed to replace the affected EHA with a serviceable one.

Source: Flight International

 

But why? What is the reason behind this AD (Airworthiness Directive)?

Several on-ground failures were reported on A350 aircraft of inboard aileron electro-hydrostatic actuator (EHA), manufactured by Moog.

Source: Airbus

Concurrent with these failures, a Dispatch Message (DM) “F/CTL INR AILERON ELEC ACTUATOR” was displayed.

Further analysis and testing by Airbus determined that in such cases the switch from damping to active mode did not occur, preventing the activation of the EHA.

This failure corresponds to a scenario called ‘’spurious damping’’ and can be detected only when the EHA is activated.

As a consequence, the EHA will not be able to take over in case of adjacent servo control failure or yellow hydraulic failure.

This condition, if not detected and corrected, and combined with other failures could result in loss of control of inboard aileron potentially resulting in inability to ensure sufficient control on the roll axis of the aeroplane.

Airbus issued Alert Operators Transmission (AOT) A27P007-15-00 to provide post-flight EHA activation instructions.

 

Based on the article “Airbus A350 Receives First Airworthiness Directive” published in Aviation Daily.