The U.S. Air Force's F-22 fighter remains subject to the longest full-force grounding of any combat aircraft in recent history, with no cause firmly identified. Meanwhile, documents show that the focus of the investigation—the onboard oxygen-generation system (Obogs)—has been a flight safety issue for many years on the F/A-18C/D Hornet, increasing the number of cases where aircrew were affected by hypoxia, or lack of oxygen, in flight.
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