The Air Force now thinks that a faulty valve installed in pressure vests — not oxygen contamination — has been causing the hypoxia-like symptoms reported by some F-22 Raptor pilots. Twelve incidents involving hypoxia-like symptoms were reported between April 2008 and January 2011, and one fatal crash has been linked to oxygen-delivery problems.At least one report even indicated toxins had been found in the blood of Raptor pilots. The Air Force briefly grounded the roughly $80 billion fleet of 180 Raptors while it failed to source the problem and thenattempted a list of fixes without results. Some attention had already been directed at the pressure vests. Now they believe a faulty valve on those vests can prevent the vest from deflating and that, they think, is the problem.
After the grounding, the Air Force then restricted how the F-22 was flown. Then it equipped the Raptors’ oxygen system with charcoal filters to remove contaminants, but those were removed after some pilots began coughing up black mucus. In June, the Air Force ordered pilots to stop wearing their pressure vests. No pilots have reported symptoms since March. In June, reports about the pressure vests suggested that they weren’t properly fitted for some pilots, but fixing the problem wasn’t expected to resolve the hypoxia-symptom issue. At that time, Air Combat Command spokesman Lieutenant Colonel Edward Sholtis said the vest had not been identified as the root cause of the problems and the vest had not been implicated as the cause of reported incidents. Last month, the Air Force was looking at issues regarding the layering of clothing and flight suits with regard to the vest.
