The Australian Transport Safety Bureau (ATSB) has ruled that oil leaks seen on the Rolls-Royce Trent 900 engines powering two Qantas Airbus A380s were caused by a loss of clamping force on oil feed pipe connections, and outlines steps the engine manufacturer is taking to resolve the issue.
Both aircraft, registrations VH-OQG and VH-OQC, experienced oil leaks in one of their Trent 900s on the Singapore-London route, says the ATSB.
On 24 February 2011, eight hours into its flight, the crew of VH-OQG detected a reduction in the indicated oil tank quantity for the No.3 engine. The crew reduced the engine's thrust to idle and continued to London.
Then, on 3 November 2011, three hours into its flight, the crew of VH-OQC received a low oil quantity advisory for the No.4 engine. Forty minutes later, the engine registered a low oil pressure warning, prompting the crew to shut down the powerplant and divert to Dubai.
In both instances, says the ATSB, maintenance personnel discovered that one of the Trent 900's external oil feed pipes had leaked in the same location.
Specifically, the leaks occurred at the external oil feed pipe connector to the high-pressure/intermediate-pressure turbine bearing support casing. The connection became loose, reducing clamping force and compromising the seal between these components.
In addition, the pipe connection was subject to higher deflection loads than Rolls-Royce had anticipated, says the ATSB.
"By the time the November event occurred, there had been 15 engine oil leaks across the A380 fleet worldwide," says the ATSB. "The engine manufacturer conducted an ongoing investigation into the oil leaks and at the time of writing this report had identified high pipe deflection loads as a significant factor."
The ATSB adds that Rolls-Royce has modified "the oil pipe clipping arrangement and revised securing methods for the pipe connection and deflector assembly." Further, Rolls-Royce has enhanced trend monitoring of oil consumption and is developing a new oil pipe design, the report says.