A four ship F-16 Fighting Falcon formation flies through the sky on a mission in northern Minnesota on Nov. 17, 2007. The F-16's, from the 148th Fighter Wing of the Minnesota Air National Guard in Duluth, were practicing mid-air refueling from a KC-135 Stratotanker in order to fulfill training requirements. (U.S. Air Force photo by Tech. Sgt. Brett R. Ewald) (Released)