While the U.S. Air Force has fielded some 250 Lockheed Martin [LMT] F-35As, at the current buy rate of 60 per year, it would take until 2048 for the service to field its planned number of 1,763. That number is in question, as the Air Force and the Pentagon Office of Cost Assessment and Program Assessment (CAPE) conduct a tactical aircraft (TACAIR) study on the service's future fighter needs--an undertaking announced last month by Air Force Chief of Staff Gen.…