Updated

The U.S. Navy and Air Force have approved a limited return to flight for their new-generation F-35 fighter jet, keeping alive the possibility that it could make an appearance at the Farnborough International Airshow in England this week.

The Pentagon said Tuesday that Navy and Air Force officials on Monday approved the flight resumption but imposed restrictions that will remain in effect until the root cause of a June 23 engine fire is identified and corrected. The entire fleet of nearly 100 planes was grounded after the fire at Eglin Air Force Base in Florida.

The F-35 is the Pentagon's most expensive aircraft program, costing an estimated $400 billion.

Three variants of the aircraft are being developed and built, one each for the Air Force, Navy and Marine Corps.