Boeing says US airlines have grounded several of its 757 planes and are trying to repair or find replacement parts because of cracks in the airflow blades of their Pratt and Whitney engines.
The cracks have affected 757-200 planes flown by Delta Air Lines, Northwest Airlines, Trans World Airlines, United Airlines and United Parcel Service since late last year - and have caused at least two failures of in-flight engines.
Boeing spokeswoman Ms Liz Verdier says the 757 has two engines and can fly on one.
She says the in-flight shutdown rate of the engines made by Pratt & Whitney, a division of United Technologies, has risen over the past year and "doesn't live up to the standards we expect from them".
But Ms Verdier says Boeing does not believe the engines pose a safety risk. "Besides, if something happens to one engine, these airplanes are certified to fly on the other engine for 180 minutes."
The US Federal Aviation Administration was informed when Pratt & Whitney issued a recommendation that airlines inspect the part six to eight months ago, but the agency saw no need to order inspections.
Pratt & Whitney is working with airlines to repair or replace the part, which it is redesigning, but the new design is not expected to be certified for use until December.
The part affected is the stator vane, a stationary blade made of steel alloy that directs airflow through the engine.
PA