"F-35 flight operations have been cleared to resume," JSF program spokeswoman Kyra Hawn said in a statement on Friday.
Pentagon officials ordered the Air Force, Navy and Marine Corps versions of the plane grounded last Friday, after the turbine cracks were uncovered aboard an Air Force version of the jet stationed at Edwards Air Force Base, Calif.
Subsequent engine tests by prime contractor Pratt & Whitney at the company's facility in Middletown, Conn., found the crack was due to "prolonged exposure to high levels of heat and other operational stressors," according to Hawn.
"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," she added.
"No additional cracks were found during inspections of the remaining [F-35] inventory," Hawn said in the statement.
As a precautionary measure, DOD and JSF program officials have tested and cleared all 17 test aircraft in the JSF fleet and are continuing rigorous inspections on the 34 operational F-35 fighters based at Air Force and Marine Corps air bases in Florida and Arizona.
Testing on the operational F-35 fleet, which began on Thursday, is still ongoing.
With a total cost estimate at more than $400 billion, the F-35 is the most expensive weapon development program in the history of the Pentagon.
The fighters' recent failures, combined with the program's massive price tag, have prompted some inside the Pentagon and on Capitol Hill to call for massive reductions or the outright cancellation of the next-generation jet.
Looming fiscal pressures tied to $500 billion in expected cuts to DOD coffers under the administration's sequestration plan have only contributed to that criticism.
In 2011, former Defense Secretary Leon Panetta officially took the Marine Corps plane off probation. Recent reports, however, claim the jet fleet, considered the most expensive acquisition program in Pentagon history, is currently $150 billion over budget, based on initial cost estimates.