PARIS -- Engine-maker Pratt & Whitney plans to finish retrofitting the F-35 Joint Strike Fighter fleet with an engine fix by early 2016, officials said.
Executives with the United Technologies Corp. subsidiary sat down with Military.com here before the start of this year's Paris Air Show to discuss the work they've done over the past year modifying the F135 engine after an F-35A caught fire during takeoff.
The pilot was unharmed in the incident, which took place last June at Eglin Air Force Base in Florida. But it crippled the plane, triggered a temporary fleet-wide grounding of the stealthy fifth-generation fighter and delayed the aircraft's planned international debut at the Farnborough International Air Show outside London.
"What a difference a year makes," Mark Buongiorno, vice president for the F135 program at the company's military engines unit, said in an interview on Sunday. "Although we weren't at Farnborough, we returned to flight within three weeks.
"We had expanded the envelope back to minimize any impact to flight tests," he added. "Immediately after that, we had validated root cause and then we've already incorporated the fix into production. We're in the process of retrofitting the entire fleet."
The Joint Strike Fighter is the Pentagon’s most expensive weapons program, estimated to cost about $400 billion to purchase 2,457 aircraft for the Air Force, Marine Corps and Navy. U.S. allies are expected to buy hundreds more. The engines alone are estimated to cost $67 billion, according to Pentagon budget documents.
Last year's F135 engine fire was traced to excessive rubbing of an air seal between two stages of blades against surrounding material known as a rub strip, Buongiorno said. "It was actually designed to have that contact," he said. "But what we actually learned from the event is ... the depth of rub that occurred, it generated a level of heat that we just had not calculated that we were going to experience."
The fix entailed cutting the air seal to have slightly more depth in a process known as pre-trenching, Buongiorno said. "You had this plate seal that was basically rubbing its way into some of the material and what that does is provides a barrier for high-pressure air to not flow back," he said. "All we did was basically just trenched out that material so now that plate seal doesn't rub against it and you still get that sealing benefit."
Pratt & Whitney so far has delivered almost 230 F135 engines to the Defense Department, Buongiorno said. Of the almost 130 F-35 aircraft currently flying in the fleet, more than 50 have been retrofitted with the engine fix, he said. The rest are scheduled to be retrofitted by early 2016. The modification is now part of production, so all new engines coming off the line contain the change, he said.
The U.S. military will display several aircraft at this year's show, including the F-15 and F-16 fighters, P-8 maritime patrol aircraft and the A-10 attack plane, but not the F-35. However, the plane's manufacturer, Lockheed Martin Corp., and Pratt & Whitney will be holding media briefings.