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The U.S. Air Force has lifted a temporary altitude restriction that required Lockheed Martin [LMT] F-35A Lightning IIs at Luke Air Force Base in Arizona to fly below 25,000 feet.The altitude limit, which ended Aug. 30, was imposed at the training base June 20 after five pilots experienced oxygen deprivation-like symptoms above 25,000 feet in May and early June. The Air Force said that while it has not identified the cause of the symptoms, it has taken steps to minimize…
