Airbus A350 operators have been ordered urgently to address a potential threat to fuel tanks arising from overheat failure of a hydraulic pump.
The A350-900 is designed with a hydraulic fluid cooling system located in the fuel tanks.
But analysis of an overheat failure mode of the aircraft's hydraulic engine-driven pump has determined that it can generate a "fast" temperature rise of the hydraulic fluid, says the European Aviation Safety Agency.
If the aircraft's fuel-tank inerting system is inoperative, adds EASA, an uncontrolled overheat of the hydraulic fluid could potentially ignite the tank's fuel-air mixture.
Airbus has responded by undertaking an in-depth revision of the A350's master minimum equipment list, the document which determines the extent to which crucial aircraft systems can be permitted to be inoperative before flight.
EASA says the revision incorporates "restrictions" to avoid uncontrolled overheat of the hydraulic system, and amended a number of items to 'no go' status.
Under an emergency airworthiness directive it has ordered immediate implementation of the master minimum equipment list changes for the A350.
Among the systems affected are air conditioning packs, hydraulic monitoring controls, and fuel-tank inerting.
EASA says the directive, which covers all A350-900 airframes, is an interim document and further related action could follow.
Airbus had delivered exactly 100 A350-900s to customers by the end of July this year. Thirteen operators use the type, which is powered by Rolls-Royce Trent XWB engines.
