The Pentagon has grounded all of its F-35s while it investigates the cause of a fire last month involving one of the jets.
In a statement late Thursday, the Defense Department said the decision was made based on initial findings from a runway fire incident June 23 at the Eglin Air Force Base in Florida. No one was hurt.
"The root cause of the incident remains under investigation," the statement said. "Additional inspections of F-35 engines have been ordered, and return to flight will be determined based on inspection results and analysis of engineering data."
In a statement, Lockheed Martin, which makes the F-35 Joint Strike Fighter, said it was working closely with its partners in supporting the investigation.
"The F-35, the Pentagon's most expensive weapons program at $399 billion, has been beset by problems that have included failing tires, engine oil leaks and issues with pilot helmets. Development costs have risen and the military services due to operate the jet have had to delay plans to operate the plane. The U.S. Marine Corps, the first user, wants the jets to be ready by next summer."