One defense official said maintainers at Eglin Air Force Base in Florida were using space heaters in some to warm the jets, which required removing a panel of the plane’s stealthy coatings. “It’s not ideal when you’re talking about a fighter jet that has to be ready to go at a moment’s notice,” said the official, who was not authorized to speak on the record.

Separately, the Pentagon’s F-35 program office on Tuesday lifted a January 18 order that grounded nine F-35B developmental test aircraft after a fuel line detached just before a training flight at Eglin Air Force Base in Florida.

Vice Admiral David Dunaway, head of Naval Air Systems Command, was briefed Tuesday on the inspections of the faulty components, and could lift flight restrictions on 16 additional F-35B model jets being used for training as early as Wednesday, according to two sources familiar with the matter.

(Additional reporting by Tim Hepher in Paris)