The ‘stand-down’ order on the entire fleet of 165 planes was issued by General William Fraser, Commander of the US Air Force Air Combat Command on May 3rd 2011. The fleet’s grounding is taking place as a precautionary measure against potential malfunction of the aircraft’s On Board Oxygen Generating System OBOGS. The OBOGS system had already been at the center of an investigation after the crash of a F-22 in Alaska on November 16th 2010. The plane, assigned to the 525th fighter squadron operating out of Elmendorf Air Force Base Alaska had crashed during a night time training flight, killing the pilot Air Force captain Jeffrey Haney. A subsequent measure implemented by the Air Force limiting the plane’s operation to below 25,000 feet confirmed the scrutiny had centered around the aircraft oxygen generation system. With an official crash investigation’s findings yet to be revealed, the latest grounding for an as yet undetermined period of time occurs pending the introduction of new safety procedures and/or corrective work on the aircraft.