A U.S. Marine F-35B taxis last year at Marine Corps Air Station Yuma, Ariz. (U.S. Marines)
The DoD office in charge of the Joint Strike Fighter suspended flight operations on the F-35B (STOVL) variant Friday for precautionary reasons after a problem was discovered with the fueldraulic system in the jet, officials confirmed for Defense News.
All STOVL variant aircraft operating at Eglin Air Force base, Fla., Marine Air Station Yuma, Ariz., and Lockheed’s production factory in Fort Worth, Texas, have been grounded while engineer teams review data on the jet.
The office made the decision after a 10:00 a.m. CST test flight at Eglin was aborted by the pilot during a conventional takeoff roll. There were no injuries to the pilot or the crew.
The abort occurred because of a failure to a propulsion fueldraulic line, which enables movement in the actuators for the STOVL’s exhaust system.
The F-35A (conventional) and F-35C (carrier) variants are unaffected.
“Implementing a precautionary suspension of flight operations is a prudent response until F-35B engineering, technical and system safety teams fully understand the cause of the failure,” wrote JPO spokesman Joe DellaVedova in an emailed statement.
“Once the causal and contributing factors are understood, a determination will be made when to lift the suspension and reinstate F-35B flight operations,” DellaVedova wrote. He added that impact on flight test operations are being assessed, and ground operations on the F-35B will continue.
A spokesman for Lockheed Martin, the prime contractor on the 5th generation fighter, directed questions to Pratt & Whitney, which designed the engine on the JSF. Pratt & Whitney has delivered 87 F-35 engines, including 40 of the STOVL variety.
“An initial inspection discovered a detached fueldraulic line in the aft portion of the engine compartment near the bearing swivel module,” spokesman Matthew Bates wrote in an emailed statement. “This component is not used in the CTOL or CV variant aircraft. A team of Pratt & Whitney and Rolls-Royce engineers is investigating the cause of the incident and working closely with Lockheed Martin and the F-35 Joint Program Office to resolve the matter.”
Bates also noted that P&W engines have successfully completed almost 25,000 hours of testing, including 4,270 flight hours.
The fueldraulic system was highlighted as a potential issue in the annual report to Congress released this week by the Pentagon’s Operational Test and Evaluation office (OT&E). The report noted that part of the fueldraulic system was removed in 2008 to save 9 pounds.
The testers warned that the fueldraulic system leaves open the chance of a sustained fire if exposed, but noted that the program office “is accepting the increased vulnerability associated with the fueldraulic system and is currently not considering reinstating the fueldraulic fuses in the production aircraft configuration.”