The U.S. Air Force will gradually lift flight restrictions placed on its Lockheed Martin F-22 Raptor fleet in response to unexplained incidents of hypoxia, or oxygen deprivation, experienced by pilots dating as far back as 2008.
Defense Secretary Leon Panetta approved a phased return to normal flight operations on July 20 after receiving assurances from Air Force leaders that corrective actions will minimize hypoxia-like events. The service leadership believes the supply of oxygen delivered to pilots, not the quality of oxygen, is the “root cause” of the problem, Pentagon press secretary George Little said July 24. “We have high confidence that we’ve identified the issue,” he told reporters.
Two changes are being made to the F-22 cockpit life support system to improve the oxygen supply. First, the Air Force will replace a valve in the upper pressure garment vest worn by pilots during high-altitude missions. “The valve was causing the vest to inflate and remain inflated under conditions where it was not designed to do so, thereby causing breathing problems for some pilots,” Little said. The upper pressure garment was suspended from flight in June. Second, a filter installed to detect oxygen contamination has been removed, increasing the volume of air flowing to pilots. Oxygen contamination has been ruled out as an issue.
In March, the Air Force Scientific Advisory Board concluded a seven-month investigation of the unexplained hypoxia incidents without identifying the “root cause,” initially thought to be tied to the aircraft’s onboard oxygen generation system. In May, the Pentagon added to earlier steps undertaken to prevent hypoxia by restricting F-22s to flying “within the proximity of potential landing locations” and assigning long-duration flights in Alaska to other aircraft.
Among corrective measures, the Air Force will install an emergency back-up oxygen system in 187 operational F-22s. After testing a modified pilot’s upper pressure garment this fall, and upon installation of the back-up oxygen system and the completion of other measures recommended by the Scientific Advisory Board and an independent analysis by NASA, the service will seek approval to remove F-22 flight restrictions and resume airspace control alert missions in Alaska.
Following the briefing last week by Air Force leaders, Panetta authorized deployment of a squadron of F-22s to Kadena Air Base in Japan. F-22s have flown more than 7,000 sorties and 9,000 hours since the last incident involving hypoxia-like symptoms on March 8. Two incidents since then involving oxygen-related issues were attributed to mechanical malfunctions.