* Exec says fault not to do with low pressure turbine
* Relatively minor adjustment needed for seals in oil system
* Sees orders this year rising to about 6,000 after air show (Adds more comments on fault, F-35, order expectations)
LONDON, July 13 (Reuters) - Executives at aircraft engine maker Pratt & Whitney said a fault on the engines for Bombardier's CSeries planes was to do with a seal in the oil system that would require a relatively minor adjustment, and not to do with the low pressure turbine.
The company, a division of United Technologies Corp, makes the engine for Bombardier's CSeries narrow-body plane, but the aircraft has been grounded since late May after a major engine failure in testing.
"The issue is a seal problem in the oil system. The fan-drive gear system is rock solid," Pratt Commercial Engines President David Brantner told journalists at a briefing ahead of the Farnborough air show.
He said it was not anything to do with the low pressure turbine, after some initial reports had suggested that was the case, and also said it was not linked to the engine failure on the F-35 fighter jet, which is also grounded and will not be flying at the air show on Monday as planned.
Graham Webb, the company's chief engineer for commercial engines, said it was a relatively minor adjustment for the CSeries engine. "We will have them back up and flying in the very near future but we have to ensure the validation is robust," he said.
Bombardier hopes to dominate the 110- to 149-seat plane market with the CSeries, built with lightweight composite materials and other technologies designed to reduce fuel burn, noise and operating costs.
It said on Saturday that Falko Regional Aircraft Limited, a lessor based in Britain, had signed two letters of intent to buy up to 24 CS100 jets, the first new CSeries deal announced since the first quarter. It is not clear whether Bombardier will be announcing any major orders during the air show.
Pratt said it expected the airshow would bring its order total so far this year to 6,000 engines, from 5,500 before the show started.
Separately on Sunday, Pratt's Canadian unit signed a deal for its PWC150C turboprop engine to power the new MA700 regional turboprop aircraft being launched by AVIC Xi'an Aircraft Company of China. (Reporting by Victoria Bryan; Editing by Mark Potter)