A new setback for the Pentagon's costliest weapons program: The military's entire fleet of 97 F-35 fighter jets has been grounded while the military probes a runway fire on one of the jets last month, reports CNN. "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," a Pentagon official says. Officials in Australia and South Korea say they haven't changed their plans to buy scores of the single-engine fighters, Reuters reports. The F-35 program, which has cost the military almost $400 billion, was grounded last year when a cracked engine blade was discovered. (More F-35 stories.)