The spate of Trent 700 engine shutdowns has been traced to insufficient lubrication of the driving-shaft locator ball-bearing in the Hispano Suiza-manufactured step-aside gearbox. This has resulted in premature fatigue and failure of the bearing, because of overheating.
According to R-R, the problem resulted from a weakness in the design of the original lubrication system, which features a 20mm gap between where the oil is injected and the bearing itself.
The UK company says that it has been studying the problem since "early this year" and has tested a modification which it is "confident" will provide the solution. This involves installation of an oil-feed system with redesigned geometry, using a design already employed on the gearbox of the larger Trent 800, and installing a new bearing. The new system increases the flow of oil lubrication to the bearing, eliminating any chance of oil starvation, and reduces operating temperatures from 170¹C to 120¹C.
"It effectively closes the gap, preventing the jet of oil from having to 'leap across' the void to lubricate the bearing," says R-R, adding that the modification is not expected to affect engine performance.
France's DGAC and the UK's Civil Aviation Authority are working to certify the modification as it is produced. R-R was planning to ship the first modification packages to Hong Kong over the weekend of 31 May/1 June.
Cathay says that it is tentatively scheduled to have the first A330 fitted with the system and test-flown by 2 June. The work can be undertaken on the wing, with just the gearbox being removed.
While the original grounding was voluntary, R-R says the airlines need approval from Hong Kong's Civil Aviation Bureau (CAB) before the aircraft are returned to service. Cathay estimates it will take until the second week of June to return all 11 A330s and four Dragonair aircraft to service. Most are at foreign airports.
The A330/Trent 700 won European Joint Aviation Authorities clearance for 180min extended-range twin-engine operations (ETOPS) flights in mid-1996. The Hong Kong CAB had approved 138min ETOPS. In early May, Cathay voluntarily suspended ETOPS flights and, later, the CAB withdrew approval. Garuda has also suspended ETOPS flights. R-R says that, when the aircraft return to service, they will not operate ETOPS flights.
Although JAA approval has not been withdrawn, R-R is unclear whether the engine/ airframe combination will have to requalify.
Source: Flight International
