THE START OF extended-range twin-operations (ETOPS) testing of the Rolls-Royce Trent-powered Boeing 777 is to be delayed by "two to three weeks", says the engine maker, after a seal crack developed in the low-pressure (LP) turbine.
The crack, in the seal arm of the LP1 turbine disc, was discovered after testing for thrust growth at "significantly higher temperatures than those required for the 90,000lb [400kn] thrust" at which the engine is being certificated.
A strip-down inspection after the test revealed a crack in a part of the seal arm, which R-R says was already earmarked for modification. "We are now accelerating that modification to put it on all production engines," the company says.
R-R claims that the problem will have "zero impact" on flight certification, but admits the test aircraft is currently operating to an N1 (fan) speed restriction. The restriction will be lifted when the modification, which involves thickening the seal arm, is in place.
Despite the delayed start to ETOPS, R-R says: "We can compress the ETOPS schedule and complete it on time by mid-March. There will be no impact on deliveries," it adds. The first aircraft is due for delivery to Cathay Pacific.
The General Electric GE90-powered 777 has begun a 300h function and reliability (F&R) test as it continues to be tested for operation in icing conditions. The F&R test is "longer than usual" says Boeing because "...we're having to repeat some of the basic certification work because of the later modifications made to the engine".
Source: Flight International
