DOD and JSF program officials have cleared the 17 test aircraft in the JSF fleet "all cleared" initial inspections, F-35 spokeswoman Kyra Hawn told The Hill on Thursday.
But officials are continuing to pour through test and flight data from those test aircraft, to see if flight conditions or any of the testing exercises could have caused the engine turbine crack that ultimately grounded the fleet, she added.
Program officials are also in the midst of rigorous inspections and evaluations on the 34 operational F-35 fighters based at Air Force and Marine Corps air bases in Florida and Arizona, according to Hawn.
Flight test data reviews are also being conducted on the operational fleet, even though those aircraft are not subjected to the same extreme conditions or operational stresses that JSF test aircraft are, she noted.
The actual F-35 fighter that suffered the engine turbine crack is undergoing a separate inspection at a Pratt & Whitney facility in Middletown, Conn. The company is the prime contractor for the F-35's main engine, dubbed the F135.
The entire JSF fleet remains banned from flight duty as DOD and program officials continue their inspection work.
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.
With a total cost estimate at over $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.
Former Defense Secretary Robert Gates put the program's Marine Corps variant, known as the F-35B, on “probation” and threatened to cancel it unless its cost and schedule problems were fixed within two years.
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.
Aside from the United States, the United Kingdom, Canada, Italy, the Netherlands, Turkey, Australia, Denmark and Norway are all scheduled to buy versions of the F-35 for their armed forces.