Defense secretary restricts flights of F-22 Raptors Concerns about the Air Force's problem-plagued fleet of F-22 Raptor fighter jets led Defense Secretary Leon E. Panetta to restrict flights of the aircraft because of problems with its oxygen systems that can cause its pilots to become disoriented mid-flight. In addition, Panetta wants a monthly progress report on the investigation into the root cause of the F-22's oxygen problems and ordered the Air Force to speed up the installation of an automatic backup oxygen system. Panetta also called on Navy and NASA personnel to find a solution. "The secretary believes that this is the prudent course of action to take at this time," Pentagon spokesman George Little said at a Tuesday media briefing. As I indicated, he will be receiving regular updates, and all options remain on the table going forward. The announcement is the latest blemish for the controversial F-22, the world's most expensive fighter jet, which was made by Lockheed Martin Corp. and has never been used in combat since entering service in 2005. Since 2008, F-22 pilots have reported more than a dozen incidents in which the jet's systems weren't feeding them enough oxygen, causing hypoxia-like symptoms in the air. Hypoxia is a condition that can bring on nausea, headaches, fatigue or blackouts. The malfunction is suspected of contributing to at least one fatal accident and led to the grounding of the entire F-22 fleet last year for nearly five months. But even after the grounding was lifted, the Air Force said investigators could not find a "smoking gun" for the problems and that hypoxia incidents continued to occur. The Air Force acknowledged two weeks ago that some of the nation's top aviators are refusing to fly the radar-evading F-22 at the risk of significant reprimand - or even discharge from the Air Force. The pilots' reluctance played into Panetta's decision, Little said. "Effective immediately, all F-22 flights will remain within the proximity of potential landing locations to enable quick recovery and landing should the pilot encounter unanticipated physiological conditions during flight," he said. This month, two F-22 pilots appeared on CBS' "60 Minutes" to discuss why they refused to fly the jet. Virginia Air National Guard Capt. Joshua Wilson and Maj. Jeremy Gordon said they would not fly the F-22 until the oxygen problems were solved. After the segment aired, other F-22 pilots have contacted Rep. Adam Kinzinger (R-Ill), a former Air National Guard pilot, and Sen. Mark R. Warner (D-Va.) to address concerns about the F-22. The congressmen last week requested additional information from the Air Force to further determine the scope of safety concerns, and on Tuesday held a teleconference with reporters to applaud the Pentagon's announcement. "I think we've got their attention," Warner said on the teleconference. Panetta "took an appropriate first step." Kinzinger said that each of the sleek, diamond-winged F-22s are vital to national security, but its capabilities are only at "80% to 90%." The F-22 is considered the most advanced fighter jet in the world because it can reach supersonic speeds without using afterburners, enabling it to fly faster and farther. According to the Air Force, each F-22 costs $143 million. Counting upgrades and research and development, the U.S. Government Accountability Office estimates each F-22 costs taxpayers $412 million. It was conceived during the Cold War in the early 1980s to beat a new generation of Soviet fighter jets in dogfights. But with the collapse of the Soviet Union, the Soviet fighter jets that U.S. military planners feared were never built. The Air Force received the last of its order of 188 planes two weeks ago. The jets are stationed at seven military bases across the country, and some are now deployed to Southwest Asia.