USA: Pratt & Whitney Engine Fix By February

United Technologies expects to solve by February an ongoing issue with its Pratt & Whitney aircraft engines that can cause excessive friction under some circumstances, chief executive Gregory Hayes said.

The problem occurs when the engine is shut down for 1.5 to 2 hours because "the top of the engine actually cools more slowly" than the rest of the engine, Hayes said in his first public explanation of the problem.

Uneven cooling creates bending in the engine shaft, requiring operators to "windmill" air through the engine for three minutes to even out the temperature before starting the engine, he said.

"You don't want to start that jet engine up with a shaft that's bent, even if we're talking about 5/10,000 of an inch," Hayes said. "You do three minutes of windmilling operation to cool the entire hot section of the aircraft down to the same temperature."

The issue this week prompted Qatar Airways to suggest it may not take delivery of the first Airbus A320neo, which is powered by the Pratt PW1100G engine, by the end of 2015 as planned. Instead, Lufthansa said it will take the first delivery.

If the engine has been idle for less than an hour or for three hours the temperature gradient is not a problem, he said. But within 1.5 to 2 hours, shaft "bowing" can cause rubbing in the engine compressor, Hayes said.

Pratt & Whitney has developed software to solve the problem through windmilling. It also has a hardware fix that will be incorporated in February, he added.

The engine already has been certified by the European Aviation Safety Agency and US Federal Aviation Administration.

Engines that already have been produced can be retrofitted, the company said.