US Air Force officials confirm that the Lockheed Martin F-35 Joint Strike Fighter has been cleared to resume flight operations after a recent grounding.

"The suspension of F-35A flight operations has been lifted for the air force," the service says.

USAF F-35 flight operations at Eglin AFB, Florida, will resume on 5 March because 4 March is a previously-scheduled maintenance training day, service officials say. The US Marine Corps' short take-off and vertical landing F-35Bs will resume flying at the Florida base on 1 March, the USAF says.

Operations at other bases are also cleared to be resumed.

 F-35A pair - USAF

US Air Force

All F-35s were grounded while the Joint Program Office investigated the root cause of a crack discovered on 19 February in a third-stage low-pressure turbine (LPT) blade deep inside the Pratt & Whitney F135 engine. The problem was discovered during a boroscope inspection on an F-35A at Edwards AFB, California, and confirmed by an eddy current inspection.

According to a JPO statement that was relayed to Flightglobal via P&W, comprehensive tests on the blade were conducted at the company’s facility in Middletown, Connecticut. “The engine in question is part of the F-35 test aircraft fleet, and had been operated at extreme parameters in its mission to expand the F-35 flight envelope,” the statement reads. “Prolonged exposure to high levels of heat and other operational stressors on this specific engine were determined to be the cause of the crack.”

No additional cracks or other signs of similar engine stress were found during inspections of the remaining F135 inventory, the JPO statement reads. It adds that the engine does not need to be redesigned as a result of this event.

Source: Flight International