Crumbling avionics lines are the latest setback for the jet, which had been riding a wave of progress.
On Aug. 2, the Air Force said 10 F-35s at Hill Air Force Base in Utah were ready for war. Forty-four days later, those planes have been grounded in the latest embarrassing setback for the most expensive project in Pentagon history.
The problem: “peeling and crumbling insulation in avionics cooling lines inside the fuel tanks,” Air Force officials said in a statement on Friday afternoon. “Engineers with the F-35 Joint Program Office and Lockheed Martin and Hill Air Force Base maintenance Airmen have conducted inspections of eight aircraft and are currently developing procedures to resolve or mitigate the issue prior to release of affected production aircraft to the field and the return of affected operational aircraft to flight operations.”
The grounding order affects 57 aircraft, some of which belong to Norway, officials said. Fifteen of them are operational jets, the 42 others are in various states of production.
The grounding interrupts a general wave of progress for the $400 billion program, which made its debut at the Farnborough Air Show in England this summer and has been getting rave reviews from pilots. (In 2014, an engine fire caused the previous high-profile grounding and scotched the plane’s first planned trip to Farnborough.)
This new restriction is sure to cast a shadow over next week’s annual Air Force Association convention, where military leaders were expected to praise the aircraft’s latest achievements.
A spokesman for Lockheed Martin, the maker of the plane, said the 42 jets on its production line would be fixed before they’re delivered.
"This is not a technical or design issue,” Michael Rein said in an email. “It is supply chain manufacturing quality issue. It will likely require depot-level maintenance to address the corrective actions for the 15 jets in the field."
The problem only affects the A model of the F-35, not the Marine Corps’ short-takeoff-and-vertical landing planes or the Navy’s carrier-capable aircraft.
"The root cause of the problem was determined to be use of nonconforming material for the tubing insulation and improper manufacturing processes during fabrication of the cooling lines," the F-35 program office said in a statement. "The nonconforming material that was used is not compatible with fuel, causing degradation of the insulation and resulting in it falling off the tubing."