Investigators are inspecting the young U.S. Marine Corps fleet of F-35Bs after a manufacturing defect was found in a number of fueldraulic lines, but program officials suggest the grounding of the short-takeoff-and-vertical-landing (Stovl) aircraft will not last long.

Officials have found six fueldraulic lines with manufacturing defects thus far in the Pentagon's 25 flyable F-35Bs. The lines carry fuel rather than traditional hydraulic fluid to enable actuator movements for F-35B's vectoring exhaust system. The aircraft, slated to be a Harrier replacement, was grounded Jan. 18 after a pilot was forced to abort a conventional takeoff during an incident at Eglin AFB, Fla., where pilots and maintenance staff are trained. Inspection later revealed a detached fueldraulic line on this aircraft, according to Matthew Bates, a spokesman for Pratt & Whitney, which makes the F135 powerplant.

The “non-compliant” units have been removed from aircraft and will be replaced, says Joe Dellavedova, the Pentagon's F-35 spokesman. Stratoflex, a division of Parker Aerospace, manufactures the fueldraulic lines. The F-35 Joint Program Office plans to fully inspect all F-35Bs for this problem.

At issue are tubes that were manufactured to the design specifications but not crimped properly, Bates says. Program sources indicate that the company has narrowed the defect to specific lots and are able to inspect first those tubes considered most suspect.

Meanwhile, the companies are implementing corrective actions to improve quality control in building the fueldraulic lines, Dellavedova says.

Neither Bates nor Dellavedova said who will pay for the repairs. But Pentagon officials typically look to the contractor to pick up the tab in the case of a defect, as with Martin-Baker ejection seats, which last year were found to have been packed backward. Some seats were recalled for rework.

The Marine Corps, the U.K. and Italy are slated to buy the F-35B.

Though the grounding is expected to be temporary, this further delays flight-testing of the B model. The Marine Corps is the customer most eager to field the aircraft, and it is first in line to declare initial operational capability, a date that has slipped repeatedly because of technical challenges or defects found in flight testing.