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The U.S. Air Force’s F-22 Raptor fleet remains grounded into a fourth month as the Air Force Scientific Advisory Board conducts a study of the F-22 and other aircraft using onboard oxygen generation systems (Obogs). The system is the suspected cause of a fatal crash on November 16 last year of an F-22 assigned to the 525th Fighter Squadron at Joint Base Elmendorf-Richardson near Anchorage, Alaska, and other incidents in which pilots experienced hypoxia, or oxygen deprivation. The length of the safety standdown–ordered May 3–has led to concern that F-22 pilots are “losing their training edge,” reported a television station in Panama City, Fla., near Tyndall Air Force Base, the F-22 training base. Before the grounding, the F-22 fleet was restricted to flying below 25,000 feet starting in January.
Air Force Secretary Michael Donley directed the service’s scientific board to conduct a “quick-look study…and recommend any needed corrective actions on aircraft using onboard oxygen generation systems.” The board was to conduct controlled flight tests “to examine subsystems identified in reported incidents,” including the pressurization system, mask and cockpit oxygen levels. The review includes the A-10, F-15E, F-16, F-35, B-1, B-2, CV-22 Osprey and T-6 Texan II. On July 21, the Air Force said, “There is no intention to direct a standdown of any other aircraft in the inventory.”
Obogs reportedly has been implicated in problems involving Navy F/A-18C/Ds, which use a Cobham system, as well as the F-22 fitted with a Honeywell system. Obogs use engine bleed air, separating out nitrogen and other components through a molecular sieve and providing a continuous supply of near-pure breathing oxygen. “The product gas is then monitored for oxygen purity and regulated before it is delivered to the pilot,” Cobham said, describing its system for the F-16. “A solid-state oxygen monitor is employed to ensure the oxygen concentration exceeds minimum physiological breathing requirements.”