Pratt & Whitney Rolls Out Engine Fix to F-35 Fighter Fleet

 - April 6, 2015, 3:34 PM
This drawing shows the location of a seal identified as the root cause of an F135 engine fire last June. (Image: Lockheed Martin)

Pratt & Whitney is installing a retrofit in its F135 engine to repair the problem that prevented the F-35 Joint Strike Fighter from making its international debut last summer. It expects to complete the fix fleetwide by early next year.

An engine fire in an F-35A that was preparing to take off for a training mission at Eglin Air Force Base, Fla., last June caused the Pentagon to ground the entire fleet, preventing the F-35’s planned international debut the following month at both the Royal International Air Tattoo and the Farnborough Airshow in the UK. The new time and place of that debut remain unannounced. Speaking with reporters in Washington, D.C., on March 24, show organizers said they do not expect the F-35 to appear at the Paris Air Show in June.

Investigators determined that the F135 fire started as a result of excessive rubbing of a polyimide plate seal between the second- and third-stage integrally bladed rotors in the engine’s compressor section. The rubbing caused excessive heating and led to the failure of the third-stage fan rotor.

Once the root cause of the engine fire was identified, Pratt & Whitney developed two fixes. The first, “controlled rub-in” procedure involves flying the F-35 in a series of planned maneuvers so that seal, which is designed to be abraded into a groove, or trench, wears in a controlled manner. The second fix was to create a “pre-trench” in the seal during the manufacturing process and retrofit the part in fighters that have been already delivered.

“We basically said, instead of rubbing it in, let’s just cut it out,” Mark Buongiorno, Pratt & Whitney’s F135 program vice president, told AIN. “We basically machined that trench in as part of the manufacturing process as opposed to letting the engine do it itself. That fix has been validated. We demonstrated that there was an insignificant loss in performance because of it and we are in the process of retrofitting the fleet to that pre-trench configuration.”

Interviewed during Pratt & Whitney’s media day in Hartford, Conn., on April 2, program officials said the retrofit has been installed on all but one of 17 system development and demonstration (SDD) fighters; the exception being an F-35 that was unavailable because it was undergoing climatic testing at Eglin AFB. The engine manufacturer is rolling out the retrofit to the remainder of the fleet using its field technicians. As of late January, F-35 manufacturer Lockheed Martin said it had delivered 131 fighters to the Department of Defense.

Buongiorno described the retrofit as “relatively minimally invasive” and accomplished in two eight-hour work shifts. He said the manufacturer is on track to complete the retrofit on the F-35Bs the Marine Corps plans to use to declare initial operational capability (IOC) this summer, and on F-35As the Air Force plans for IOC in 2016.