The F-35 has been cleared for flight operations after a precautionary grounding when inspectors found a .6 in. blade crack on a 3rd-stage engine turbine Feb. 19.
The crack was found in AF-2, which has been used for testing the aircraft at the edge of its operational envelope. "The engine in question is part of the F-35 test aircraft fleet and had been operated for extended time in the high-temperature environment in its mission to expand the F-35 flight envelope," according to a statement from Lt. Cdr. Kyra Hawn, an F-35 spokeswoman. "Prolonged exposure to high levels of heat and other operational stressors on this specific engine were determined to be the cause of the crack."
Officials at engine manufacturer Pratt & Whitney have indicated this was a one-off issue, not jeopardizing other engines in the fleet.
No additional cracks were found in the fleet during post-grounding inspections.
However, this incident raises questions about the durability of the engine which pushed to its limits. AF-2 was used to test the new horizontal tail skin, and so it was run through many extra afterburner tests. Officials are sure to implement additional inspections and monitoring actions to understand more about the durability of these engines in extreme conditions.
Seventeen aircraft are being used for flight testing at NAS Patuxent River, Md., and Edwards AFB, Calif. The remainder are used for rudimentary flight training at Eglin AFB, Fla., and MCAS Yuma, Ariz.
The flight training birds are very limited in their operations to essentially conducting takeoffs, landings and flying in the pattern. So, there is likely less concern about their engines as they are not being pushed to extremes.