The mission of the VC-25 aircraft -- Air Force One -- is to provide air transport for the president of the United States. The presidential air transport fleet consists of two specially configured Boeing 747-200B's -- tail numbers 28000 and 29000 -- with the Air Force designation VC-25. When the president is aboard either aircraft, or any Air Force aircraft, the radio call sign is "Air Force One." (U.S. Air Force photo by Senior Airman Elizabeth Slater)