USAF Indefinitely Grounds F-22 Raptors By SCOTT FONTAINE and DAVE MAJUMDAR Published: 5 May 2011 17:48 The U.S. Air Force has grounded all of its F-22 Raptors until further notice because of potential malfunctions in the fighter jets' oxygen-generation system. The On-Board Oxygen Generating System has been under investigation since a November 2010 crash in Alaska. (File photo / U.S. Air Force) Gen. William Fraser, commander of U.S. Air Combat Command, ordered a stand-down of the 165-plane fleet May 3, ACC spokeswoman Capt. Jennifer Ferrau said. Ferrau didn't immediately know how long the Raptors will be out of service. The On-Board Oxygen Generating System (OBOGS) has been under investigation since an F-22 crashed in November just outside Joint Base Elmendorf-Richardson, Alaska. Until the stand-down, Raptor sorties had been restricted to an altitude of 25,000 feet or below for training missions because of the potential malfunctions. The limits were "designed for mishap prevention and is a prudent measure to ensure the OBOGS are operating safely," ACC spokesman Col. William Nichols said in March, when the command first publicly disclosed the investigation. An OBOGS malfunction can be potentially life-threatening, said Hans Weber, who sat on the U.S. Federal Aviation Administration's Research, Engineering and Development Advisory Committee, and is president of Tecop International, a San Diego consulting firm. "It's a big deal if you're at high altitude and you run out of oxygen," Weber said in a March interview. At 50,000 feet, a human being has less than 10 seconds of useful consciousness, he said. The 25,000-foot altitude restriction would allow the pilot to quickly dive below 18,000 feet, where the atmosphere has enough oxygen to ensure prolonged survival in case of an emergency. "It would take you so long when you're way up high, you may black out before you make it to a safe altitude," Weber said.