(Bloomberg) -- Lockheed Martin Corp. halted deliveries of its F-35 jets to the U.S. Air Force for much of this month because of a flaw in a system used to prevent explosions if fuel tanks are hit.

Flaws in tubing used to circulate inert gas into fuel tanks to prevent explosions were found in 14 of 24 Air Force models of the fighter jet inspected, the Pentagon’s F-35 program office said in a previously undisclosed June 5 memo that highlighted the halt in deliveries.

But Lockheed said Wednesday that it resumed deliveries, with two of the fighter jets provided on Tuesday. It recommended that flights be restricted “within 25 miles of lightning or thunderstorms” as a safety precaution while the contractor works with the Defense Department’s F-35 program office on a corrective plan.

The Air Force plans to buy 1,763 F-35s, the most in the program that also provides models for the Marine Corps and Navy.

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