A minor design change to the Rolls-Royce Trent XWB, which will power the Airbus A350, may push its first test flight back by "a few weeks".
The powerplant is already fitted to Airbus's A380 MSN1 flying testbed in the number two position on a hybrid A350/A380 pylon and has undertaken ground tests.
The heavily-instrumented engine is fitted with the highest ever number of sensors for a R-R civil programme. These will measure 1,200 individual parameters - twice as many as any previous evaluation - and add 600kg (1,300lbs) of weight to the test engine.
Speaking in Toulouse, Chris Cholerton, R-R director of the Trent XWB programme, said specific fuel consumption tests are tracking ahead of expectation for typical early build engines and that it is the company's expectation that the A350's engine will be the "world's most efficient civil turbofan".
The engine-maker completed its required 150h endurance test in September, as well as a bird strike test that saw four 1.1kg (2.5lb) birds ingested while at maximum take-off power.
During the endurance testing, Cholerton said R-R discovered damage on the engine's "rotating air seal that separates the [intermediate pressure] turbine from the back of the [low pressure] turbine"
"That's an issue we can easily resolve," he said, adding an updated design has already been manufactured.
"We may elect to change that prior to flight, because we can, it's simple to do," he said. "We can do it here in Toulouse. We can still be flying the flying test bed over a year ahead of first flight. We want to test the final production standard of part, that's a good thing to do for our maturity objectives."
If R-R opts to install the modification before beginning an estimated 175h of flight trials the engine will have to be removed from the A380, sliding the engine's first flight by "a few weeks".
As of 10 November, eight engines had accumulated approximately 1,200h of testing, running the engine to as high as 100,000lbs.
Airbus has not disclosed a specific time of the A380 testbed's flight, only saying the Trent XWB flight trials would start in "the coming weeks".