"Government and industry engineering teams investigating the origins of a failed propulsion fueldraulic line on an F-35B Short Takeoff and Vertical Landing (STOVL) variant have identified the probable cause and are developing a return to flight plan to lift the suspension of flight operations," the F-35 Joint Program Office (JPO) says.
According to the JPO, engineers have ruled out any design or maintenance problems. "Evidence revealed a quality discrepancy from the company that produces the fueldraulics line," the JPO says. "The investigation determined the line was improperly crimped."
The investigating team found that six other aircraft had the same manufacturing defect. The faulty parts have been returned to F-35 propulsion system prime contractor Pratt & Whitney for replacement. The fueldraulic line is built by Stratoflex. The company, along with Rolls-Royce and Pratt &Whitney, has "instituted corrective actions to improve their quality control processes and ensure part integrity," the JPO says.
The fueldraulic line powers the actuator movement for the F-35B's STOVL vectoring exhaust system. Instead of traditional hydraulic fluid, the system uses fuel as the operating fluid to reduce weight.
NAVAIR and the JPO are currently "developing a return to flight plan which details the removal and inspection requirements of currently installed fueldraulic lines on the 25 F-35B variants affected by the flight suspension." The B-model has been grounded since 18 January, but the US Air Force's F-35A and US Navy F-35C were not affected.