In this image released by the U.S. Navy courtesy of Lockheed Martin, the U.S. Navy variant of the F-35 Joint Strike Fighter, the F-35C, conducts a test flight February 11, 2011 over the Chesapeake Bay. (Photo by U.S. Navy photo courtesy Lockheed Martin via Getty Images)
The Pentagon says it has lifted an order that briefly grounded its fleet of F-35 fighter jets.
The Fort Worth, Texas-built Lockheed Martin jets were grounded on Feb. 21. That was after the discovery of a small crack in the turbine blade of an engine in one F-35 at Edwards Air Force Base, Calif.
On Thursday evening the Pentagon said all 51 planes had been cleared to resume flight operations.
It said prolonged exposure to high levels of heat and other unspecific "stressors" were determined to be the cause of the crack. No additional cracks were found.