The inspection at Edwards Air Force Base in California Friday revealed a crack on a turbine blade in the jet engine of an F-35A plane. The modern aircraft is the Air Force version of the sleek new warplane.
A total of 51 planes were grounded pending the investigation. In a statement, the Pentagon said it was too early to know whether the entire fleet was affected by the engine issue, but was suspending all flights until the investigation was completed.
Officials said the engine was being shipped to Pratt & Whitney, the United Technologies Corp unit in Conn. that builds the engine, for a thorough evaluation and root cause analysis.
The nearly $400 billion F-35 Joint Strike Fighter program is the Pentagon's biggest weapons program. The grounding comes as the program has been drawing criticism from Congress for its expense and delays.
The Associated Press contributed to this report.