The Defense Department believes it knows how an F-35A caught fire in June and the head of the program believes he will have a root cause analysis complete as to why it happened by the end of the month.
F-35 Program Executive Officer (PEO) Air Force Lt. Gen. Christopher Bogdan said Wednesday the F135 engine of the impacted jet was put through maneuvers three weeks before the fire that were “well within the envelope” of the airplane. Bogdan said because the engine hadn’t been what he called “fully burned-in,” engine fan blades and a rubber material rubbed together, causing an engine fan to overheat, reaching 1,900 degrees Fahrenheit. The engine fan was only supposed to reach 1,000 degrees Fahrenheit, Bogdan said.
The overheating caused the engine to develop microcracks, which Bogdan said continued to grow into what he called “high-cycle fatigue” over the span of three weeks. On the day of the mishap, Bogdan said, the engine’s fan blade system cracked too much and cracked on takeoff, setting off a chain reaction of events that lead to the fuel tank catching fire.
“We know very, very precisely what happened,” Bogdan told an audience at the ComDef conference in downtown Washington. “We’re really close (to knowing why). We went from 138 different possible reasons. We’re down to four.”
Bogdan said a combination of those four reasons could be why the fire started. But he also warned that this would not be the last mishap on the F-35. Bogdan said Pratt & Whitney, developer of the F135 engine, would pick up the tab to retrofit 156 engines with “some kind of solution” and that future problems with the engine would have risk split between DoD and the company.
“Pratt & Whitney’s reaction to this problem…has been very good,” Bogdan said. “They’ve clearly recognized this is a problem they need to solve.”
The initial F-35A conventional Air Force variant fire took place June 23 and eventually led to DoD grounding its entire fleet. DoD lifted its department-wide grounding July 14 (Defense Daily, July 15).
The F-35 is developed by Lockheed Martin [LMT] with subcontractors BAE Systems and Northrop Grumman [NOC]. Pratt & Whitney is a division of United Technologies Corp. [UTX].