U.S. Air Force Air Education and Training Command (AETC) found that damage to an F-35Athat caught fire last year after a catastrophic engine mishap totaled more than $50 million.
With such damage, “It is likely parts will be returned to the F-35 spares inventory as appropriate,” says F-35 Joint Program Office spokesman Joe Dellavedova. “Other components of the aircraft will be evaluated for potential reuse in other aircraft or training systems.”
The F-35A, part of the 58th Fighter Squadron, caught fire after taxi and before takeoff June 23, 2014, during a training mission at Eglin AFB, Florida. The pilot safely aborted takeoff and exited the aircraft.
The fire prompted a fleetwide grounding and led to the notorious absence of the F-35B at the Royal International Air Tattoo outside London and Farnborough air show last year. Basic flying operations were restored, only with G and speed limits, less than one month following the incident. The fleet is flying normally today.
AETC’s accident investigation validates the findings of the Pentagon and Pratt & Whitney, the F135 engine manufacturer.
The board “found the cause of the mishap was catastrophic engine failure. The engine failed when the third-stage forward integral arm of a rotor fractured and liberated during takeoff,” AETC says in an announcement. “Pieces of the failed rotor arm cut through the engine’s fan case, the engine bay, an internal fuel tank and hydraulic and fuel lines before exiting through the aircraft’s upper fuselage.” Leaking fuel and hydraulic fluid ignited and burned the “rear two thirds of the aircraft,” the announcement says.
Friction caused the integral arm in the third-stage rotor to break. The fix from Pratt is to “pre-trench” the polyimide foam lining between the stators and knife-edge seal forward of the third-stage integrally bladed rotor. The mishap occurred because of a low tolerance, causing friction.
The problem had not been seen in earlier jets because they were flown in gradually more complex flight profiles, effectively “burning in” that trench. The fix is being added to the existing fleet and will be cut into the production line.
The next big milestone for the F-35 is initial operational capability for the U.S. Marine Corps with the “B” model. Though the milestone was slated for July 1, USMC Deputy Commandant for Aviation Lt. Gen. Jon Davis says it will likely be later in the month due to an operational readiness inspection.
The fire “event had negligible impact on service IOC timelines,” Dellavedova says. Six F-35Bs just wrapped up operational testing on the USS Wasp last month.