WASHINGTON, Sept 2 (Reuters) - United Technologies Corp this week will begin testing a design change to fix the problem that caused a massive engine failure on a Lockheed Martin Corp F-35 fighter jet in June, according to two sources familiar with the program.
The failure of Pratt & Whitney's F135 engine grounded the entire F-35 fleet for several weeks this summer and prevented the newest and most advanced U.S. warplane from making its international debut at two UK air shows. Flights have resumed but with certain restrictions on speed and other maneuvers.
Deliveries of the F135 engine by Pratt, a unit of United Technologies, have been on hold since the June 23 incident at Eglin Air Force Base in Florida when an engine on an Air Force F-35A broke apart and caught fire as it was preparing to take off for a training flight.
The sources, who were not authorized to speak publicly, said the testing would be done at Pratt's facility in West Palm Beach, Florida after weeks of preliminary work. The tests had been expected to start last week, but were delayed while engineers grappled with how to control the vibration of the engine as it was being tested, according to one of the sources.
Pratt spokesman Matthew Bates said the company would conduct engine and rig testing this month to validate the suspected root cause of the engine failure and test a proposed solution.
Bates said the company was working on a solution that would allow the fleet of F-35 test aircraft to resume the full range of flight tests in the near term.
Pratt was also working on tests that would clarify what changes were needed for the fleet of operational jets.
As of Sept. 2, the Pentagon's F-35 program office said it had 84 training jets and 19 test aircraft for a total F-35 fleet of 103 jets.
Bates said the company hoped to share more details about the proposed fix when the tests were completed.
He said Pratt also hoped to wrap up talks soon with the Pentagon about the next two batches of engines.
"We look forward to concluding our negotiations for the 7th and 8th lot of engines shortly," Bates said.
Separately, Pratt has sued A&P Alloys Inc, a Massachusetts titanium supplier, for fraud and breach of contract after questions over the material led Pratt to briefly suspend engine deliveries.
Officials with Pratt and the F-35 program office last week said the material did not pose a risk to flight safety. (Reporting by Andrea Shalal; editing by Andrew Hay)