All Grounded F-35 Test Jets to Return to Flight

After weeks of being grounded the three late model F-35 Lighting II Joint Strike Fighter test jets have been cleared to fly. The jets' return to flight comes after program officials tweaked maintenance procedures which had led to the failure of two generators and an oil leak during a test flight of an F-35A on March 9.

A March 25 email from the Pentagon's F-35 office states:

Flight clearance was reinstated after an investigation and test data indicated a maintenance procedure resulted in excess oil remaining within the [alternate engine starter/generator] lubrication system. Previous maintenance procedures could allow a small amount of extra oil to remain within the generator following servicing. Under some conditions, the extra oil that is churning inside a narrow air gap within the AES/G could cause internal temperatures to increase. It was assessed that high temperatures led to the generator failures. Maintenance documents have been amended to provide improved engine starter/generator servicing procedures."

The backup generator kicked in during the March flight of an Air Force test F-35 known as AF-4, allowing the plane to safely return to Edwards Air Force Base in California.

The two most recent production F-35s have also been cleared to fly and the grounding did not have a "significant" impact the JSF's development or production, according to the e-mail.