TOULOUSE, France—Airbus Group SE has encountered delays in flight trials of its new A320neo single-aisle jet because of a problem on one of the engines, although the program remains on track for its first plane delivery this year.

Flight testing is currently on hold for the A320neo powered by PW1100G engines from Pratt & Whitney, an arm of United Technologies Corp., said Didier Evrard, the head of programs for Airbus's commercial jetliner unit, on Thursday. The delay should only be a matter of days, he said.

The problem relates to clips that hold a seal in the area of the high-pressure compressor of the engine, Mr. Evrard said. Some batches of the component appear not to have had proper temperature treatment.

The A320neo, the replacement to the A320 single-aisle jet now in service, is the backbone of the plane maker's future production. Meeting its planned launch date is critical for Airbus, which is battling rival Boeing Co. to win new orders in the key market of narrow-body aircraft.

A spokeswoman for Pratt & Whitney said the engine maker understands the nature of the problem and is addressing it.

"We are confident that the A320neo with Pratt & Whitney engines will resume flight tests in the coming weeks," spokeswoman Sara Banda said. "And we remain on track to support an entry into service in the fourth quarter of this year."

For Pratt & Whitney, the delay is an unwelcome wrinkle in the rollout of one of the company's most crucial products—a new family of engines built around a sophisticated gearing mechanism that the company says will produce major gains in fuel efficiency and reductions in engine noise.

The engine is otherwise performing as expected, Airbus's Mr. Evrard said, adding the target to deliver the first A320neo before the end of the year seems "reasonable."

The problem that has delayed the A320neo flight tests hasn't occurred on other engines in Pratt & Whitney's PurePower engine line, such as those for the Bombardier C-Series, a person familiar with the matter said.

Airbus, which began A320neo flight trials with the Pratt & Whitney engine in September, said it logged 139 flights and more than 420 hours. Those tests have been interrupted for a few weeks since the problem was discovered, Airbus said.

Airbus also offers the A320neo with engines made by CFM International, a joint venture of General Electric Co. and Safran SA. That model is due several months later. Airbus this month began flight testing an A320neo with the engine, called the Leap-1A.

Mr. Evrard said he was comfortable that the Leap-1A engine would meet fuel-consumption targets amid reports that early versions of the turbine aren't as efficient as intended. "The Leap will get there," Mr. Evrard said.

Write to Robert Wall at robert.wall@wsj.com and Ted Mann at ted.mann@wsj.com

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