Engineers working on the Lockheed Martin F-35 Joint Strike Fighter (JSF) have identified the likely culprit behind a fueldraulic line failure on 16 January that led to the temporary grounding of the US Marine Corps' B-model aircraft.

"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."

 RAF F-35

 Lockheed Martin

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.

Source: Flight International