Flight restrictions on F-35 since June will be lifted

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WASHINGTON, D.C. — A new government report says the flight testing restrictions that have been in place on the F-35 ever since the Air Force version of the jet caught fire in late June, will be lifted this month.

The Pentagon’s office of the Director of Operational Test & Evaluation in late January released its annual report to Congress, which investigates weapons programs across all military services to identify common problems and other themes in operational testing of Department of Defense weapons systems. 

This year’s report includes a lengthy section on the F-35 Joint Strike Fighter program. According to the report, after an F-35A aircraft assigned to the training center at Eglin AFB, Florida, experienced an engine failure on take-off, which caused it to burst into flames on June 23, the F-35 program office instituted a series of actions that affected flight operations for both the fielded production aircraft and the test aircraft.

One of those actions — the institution of engine power restrictions during flight testing — remains in place today.

After a fleet-wide suspension of flights that was ordered in light of the fire was lifted on July 8, the program office began permitting engine runs up to 30 percent power for engines that had completed special inspections with a piece of equipment called a borescope.

Those operating limitations have since been incrementally revised to allow flight testing to continue, but although aircraft in what is known as the “flight sciences” series of each variant had been cleared to continue testing without engine restrictions, the rest of the test fleet continues to conduct flight testing with the restrictions in place. 

The program plans to remove all engine‑imposed restrictions from the developmental test fleet by the end of February, after modifications to the engines of each aircraft are complete.

The report says the engine failure created a “debt of flight sciences testing” on the F-35A that will need to be overcome in 2015 and early 2016 to maintain the current release schedule for the delivery of software that provides full war fighter capability for the jet.

The report also gives specifics on what caused the June engine failure.

On Oct. 10, the program confirmed that excessive rubbing between a seal and the titanium interface of a rotor led to the engine failure. Friction from the rubbing created excessively high temperatures within the titanium rotor, creating small cracks that eventually led to “catastrophic failure of the rotor during the take-off on June 23,” the report says.

Defense officials say the challenges won’t delay the stealth jet’s operational timeline or its arrival at Hill Air Force Base, which will be home to the first three operational F-35 squadrons and will begin receiving what will ultimately be a total of 72 jets in September.