F-22 hypoxia might have been caused by an inflatable vest worn by pilots to prevent damage to their lungs, according to CBS News. The F-22 Raptor is considered by many to be America’s most advanced fighter plane, with each plane costing roughly $143 million to manufacture. When you’re shelling out that much money for a single jet, the last thing you want is to hear that your pilots are having trouble keeping their oxygen levels under control.

That’s precisely what was happening to those who were flying the F-22, much to the dismay of military officials who were attempting to justify the cost of their plane to the powers that be. Despite several investigations into the matter, authorities could not identify the source of the problem, which, ultimately, caused the F-22 to be grounded until these issues could be solved. The fighter, for all intents and purposes, was out of commission.

Those working behind-the-scenes couldn’t put their finger on why, exactly, their pilots were suffering from hypoxia. That is, of course, until Major General Charles Lyon’s team of investigators set their sights on an inflatable vest designed to prevent the pilot’s lungs from exploding when they reach high altitudes.

“The vest was inflating every time you pull G’s in the aircraft and then staying inflated which was making it more difficult to take air,” Col. Robbins explained. He added, “No one has gotten to the point where they’re completely, where they’re delirious. They’re still able to function, still able to bring the aircraft back safely.”

Of course, two instances of oxygen depravation were recorded during a few test flights following the removal of the vest, though General Lyons seems to think this was a result of some unrelated mechanical issues. Until all of these issues are hammered out, the expensive F-22 Raptor may spend more time on the ground than in the air.