Pilots Kept Losing Oxygen and the Military Had No Idea Why. Now There’s a Possible Fix.

Officials from both services have pointed to two main causes of these events: flaws in the system that provides oxygenated air for pilots to breathe, and an environmental-control system that is unable to maintain the appropriate air pressure inside the cockpit. The former has resulted in episodes of hypoxia. The latter caused some pilots to suffer decompression sickness, comparable to what deep-sea divers can experience if they do not surface slowly enough for nitrogen to be removed from their bloodstream and expelled through their lungs.

In earlier decades, fighter jets carried liquid oxygen onboard for pilots flying at high altitudes. But over the past 20 years, both services have been transitioning to a system that collects air from outside the aircraft and filters nitrogen from it until it is safely breathable. The change was an attractive safety feature because liquid oxygen can be a fire hazard, and the new system offered, in theory, a functionally limitless supply of air. But the newer system also lacked sensors to monitor the air quality and had no alarm that could alert pilots to any problems. After Navy pilots reported increased physiological problems as these oxygen concentrators aged, the devices were taken apart and examined. Sailors who work on the planes found a surprising amount of wear inside, including contamination from engine exhaust. This led Navy officials to recommend that certain oxygen-system parts be regularly inspected regardless of their performance and to redesign the internal nitrogen filter.