U.S. grounds all F-35 jets in wake of runway fire incident

WASHINGTON, July 4 (UPI) -- Late Thursday, the Pentagon announced it had grounded its entire fleet of F-35 jets as it continues to look into the cause of a jet engine fire on a runway early last week.

The fire and subsequent grounding of all F-35 Joint Strike Fighter jets is the latest in a series of hiccups that have plagued the Pentagon's most expensive weapons program to date. Built by defense contracting stalwart Lockheed Martin, the $399 billion program has endured failing tires, engine oil leaks and even problems with pilot helmets.

The Pentagon, Boeing and Pratt & Whitney -- the engine unit of United Technologies, which built the jet's engine -- are looking into the fire that erupted at Eglin Air Force Base in Florida on June 23.

"The root cause of the incident remains under investigation," the Pentagon confirmed in a statement.

Until that investigation is complete, the F-35 jets won't return to the skies. "Defense Department leadership supports this prudent approach," the Pentagon said.

Several F-35 test jets were set to perform as part of an international air show in the United Kingdom next week. Preparations for that event will continue as planned, the Pentagon said, but a final decision on whether the jets will actually fly won't come until early next week.