EASA Directive Targets A350 Hydraulic Leak Risk

Hydraulic fluid exposure can contaminate a key flight control data interface on Airbus A350s and in extreme cases lead to uncommanded flight control surface movements, prompting the manufacturer and European Union Aviation Safety Agency (EASA) to develop an inspection program.

An EASA airworthiness directive (AD) issued April 30 reveals the issue and mandates Airbus-recommended checks and, if necessary, part replacements. EASA’s directive is based on an Airbus bulletin issued to operators April 30.

The issue affects flight control remote modules (FCRMs) found in elevator, rudder, aileron and spoiler systems. Leaking hydraulic fluid from a related servo can damage the FCRMs, which could cause anomalous movements of the related surfaces. The directive, which bypassed the no public comment stage due to the issue’s immediacy, orders inspections in as little as 24 days from the May 7 effective date for a certain subset of aircraft.

“An occurrence was reported of loss of control of an outboard aileron surface. Subsequent investigations determined that the electronic card of the FCRM of that aileron had been contaminated by hydraulic fluid,” the directive said. “Due to similarity of design, elevator and rudder, FCRM could be subject to the same failure mode. This condition, if not detected and corrected, could lead to runaway of rudder or elevator surface, possibly leading to loss of control of the airplane.”

The Airbus bulletin calls for replacing any FCRM exposed to hydraulic fluid and “prohibits swapping elevator and rudder FCRM with aileron and spoilers FCRM,” said the directive, which is based on the Airbus instructions. Going forward, FCRMs must be swapped as soon as leaks are discovered, the AD said.