The US Air Force has ordered a temporary pause in flight operations for 15 Lockheed Martin F-35A fighters after discovering peeling and crumbling insulation in avionics cooling lines inside the fuel tanks, the service says in a statement today.

During a routine maintenance check, insulation from an avionics cooling line within a fuel tank was found detached from the line of one F-35A fighter, the F-35 Joint Programme Office said today. A supplier used nonconforming material for the tubing insulation which was not compatible with fuel and caused the insulation to deteriorate, according to the JPO.

“This insulation could, under certain circumstances, obstruct fuel flow in and out of various fuel tanks,” the JPO says. “Thorough review of production records indicates the problem is limited to only 57 F-35A aircraft.”

The issue affects 15 aircraft, including 13 USAF fighters and two Norwegian fighters. Four of the 15 fighters, two USAF and two Norwegian, were housed at Luke Air Force Base, Arizona, for training. One USAF F-35A completing operational test and evaluation at Nellis Air Force, Nevada and 10 aircraft at Hill Air Force Base, Utah will not fly.

The maintenance issue will also affect 42 production line aircraft, which the USAF and partner nations have not yet accepted, a USAF spokeswoman told FlightGlobal. Those partner nations include Norway, Japan, Israel and Italy, a Lockheed spokesman confirmed. Lockheed says the supply chain issue should not affect negotiations with the USAF or Norway.

“This was an issue where we got a bad part,” he says. “It has nothing to do with the capabilities of the airplane, contract negotiations or weapons employment. I don’t want this to get mixed up with other SDD [System Development and Demonstration] issues we’ve dealt with in the past, we haven’t had any of these issues.”

Lockheed has determined the issue is limited to the conventional takeoff variant based on when the parts were installed on the jet, Lockheed says. Although the F-35 fighters are common, the three variants’ wing designs are distinct and the tubes delivered to Lockheed were designed for the A model wings, Lockheed says. The company is working on finding the best way to replace the tubes on the 42 production aircraft, but has not determined if that change will cause a delay, he adds.

Source: FlightGlobal.com