Detached Fueldraulic Line Grounds F-35B

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The U.S. F-35 Joint Program Office has grounded its young fleet of F-35Bs after the failure of a propulsion fueldraulic line during a takeoff attempt last week at Eglin AFB, Fla.

The Pentagon’s air worthiness authorities, which have oversight of airspace issues for the integrated test teams at NAS Patuxent River and Edwards AFB, Calif., and Naval Air Systems Command officials, who oversee airspace for the F-35B at Eglin AFB, Fla., and Marine Corps Air Station Yuma, Ariz., made the decision to ground the fleet pending further investigation, according to Cdr. Kyra Hawn, an F-35 spokeswoman.

The grounding impacts 25 F-35Bs that have been delivered to the Marine Corps and those at prime contractor Lockheed Martin’s Fort Worth assembly facility. Ground-based static operations will continue.

On Jan. 16, an F-35B experienced a propulsion fueldraulic system failure while the pilot was initiating a conventional takeoff roll. The F-35B is unique among the three Joint Strike Fighter variants because it can takeoff vertically – like a Harrier -- using an inventive lift-fan incorporated into the propulsion system. The system relies on vectoring the exhaust nozzles for the exhaust system. This fueldraulic line controls the actuators for the short-takeoff-and-vertical-landing vectoring exhaust system.

During the incident, the pilot aborted the takeoff. No one was injured and the aircraft was towed to a maintenance hangar.

Officials at Pratt & Whitney, which manages the propulsion system, say the fueldraulic line in the aft portion of the engine compartment had become detached near the bearing swivel module. Rolls Royce provides these modules.

“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,” Hawn says. “Once the causal and contributing factors are understood, a determination will be made when to lift the suspension and reinstate F-35B flight operations.”

Determining the cause is a top priority for the F-35 team, she says.

Flight testing on the F-35B had been ahead of plan before this incident. Hawn says the program office is assessing the impact of the grounding to the testing schedule.

Officials will want to find out how the fueldraulic line became detached, and they are likely inspecting the remainder of the fleet to see if these lines are loose or detached on any other aircraft.

The U.S. Marines are the first customer planning to declare initial operational capability, and delays in testing can impact the service’s ability to do so.

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