Airbus is working on a software modification that is expected to address a hydraulic engine driven pump (EDP) failure mode that the manufacturer and regulators have determined poses a fuel tank flammability risk.
The issue centers on "a fast temperature rise of [EDP] hydraulic fluid," the European Aviation Safety Agency (EASA) explains in a related emergency airworthiness directive (AD) issued Aug. 22. "This condition, if not detected and corrected, combined with an inoperative Fuel Tank Inerting System (FTIS), could lead to an uncontrolled overheat of the hydraulic fluid, possibly resulting in ignition of the fuel-air mixture in the affected fuel tank."
The AD, effective Aug. 24, orders A350 operators to revise their master minimum equipment lists (MMELs) immediately to reflect the risk. The update, which Airbus recommended in an Aug. 21 MMEL-revision operator alert, changes 24 MMEL items to "no-go," meaning they must be fixed before the affected aircraft can fly in revenue service.
Airbus says it detected the issue in an operator's data gathered as part of routine, entry-into-service monitoring using the A350's aircraft condition monitoring system. Analysis of other operators' data confirmed that it was not a one-off event, prompting the OEM to act.
"Going forward and in line with the continued airworthiness process to mitigate any risk to safe operation, Airbus’ experts are working short-term on an easy retrofit-able software fix to the monitoring and control system," the OEM says. It did not provide a timeline for the fixes.