Air Force Grounds 'Combat Ready' F-35s Over Coolant Line Flaws

Seven weeks after the Air Force declared its first F-35 jets combat ready, 10 of the aircraft aren't flying after service mechanics discovered "peeling and crumbling" insulation wrapped around lines that carry liquid to cool combat systems and computers.

The poor insulation is suspected on 57 aircraft, including 42 on Lockheed Martin Corp.'s production line. The issue is not a design flaw with the aircraft but instead caused by manufacturing quality glitches with one of two subcontractors which make the 18 lines through which the coolant flows, according to an Air Force statement and an interview with a service official, who asked not to be identified.

If not fixed, the crumbling insulation could become lodged in the lines connecting the aircraft's wing and fuselage fuel tanks causing potential overpressure or underpressure that "may cause structural damage to the fuel tanks," according to a statement sent Friday to House and Senate defense committees.

"The issue was discovered during depot modification" of an Air Force jet and has resulted this month in a "temporary pause in flight operations," according to a separate statement from the service. Ten of the 15 aircraft not flying are located at Hill Air Force Base, Utah, home of the service's first combat-ready squadron. The other five aircraft don't have the flawed insulation and continue to fly regular sorties, the office said. Two aircraft delivered for Norway are also not flying, said the official.

'Corrective Actions'

Fourteen of the aircraft that need to be fixed on the production line belong to Norway, Italy, Japan, and Israel, according to Air Force data.

Lockheed Martin spokesman Michael Rein didn't have an immediate response when contacted by Bloomberg News. The Air Force has taken delivery of 100 F-35A models but the Pentagon's Defense Contract Management Agency has suspended delivery of additional aircraft "until corrective actions" are in place, according to the Air Force statement.

"Lockheed Martin has begun developing the repair process for these aircraft," the Air Force statement said.

The official, who follows the F-35 program closely, said the Air Force, Lockheed Martin and the Pentagon program office know precisely which planes have the suspect insulation, so the overall program impact is not widespread.

Still, it's unknown at this point how long the aircraft will be grounded and when the 42 aircraft currently on Lockheed Martin's production line will be modified with new insulation, the official said. Air Force and Lockheed engineers should finalize a formal recovery plan by next week, the official said.