An Asian tour designed to test reliability of the A350-1000 was postponed after engineers discovered a problem with its Trent XWB-97 engines, Challenges magazine reported last month.

Two people familiar with the issue said the problem affected a part attached to the combustor inside the engine, the most powerful powerplant developed by the UK engine maker.

“We are working closely with Airbus to support their plans to begin functional and reliability testing in the coming weeks, having addressed a quality finding in an engine component,” a Rolls-Royce spokesman said.

An Airbus spokeswoman said it was still on schedule to win safety certification in the fourth quarter.

The so-called route-proving tests mimic airline operations and are designed to put the 366-seat aircraft through its paces on the long-haul trips for which it is designed.

The first delivery to inaugural customer Qatar Airways is scheduled before the end of the year.