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U.S. Air Force Lt. Col. Nathaniel Halley, 20th Fighter Wing instructor and evaluator pilot, performs an F-16 Viper pre-flight inspection before a functional check flight (FCF) at Shaw Air Force Base, South Carolina, Nov. 30, 2021. An FCF determines whether an aircraft airframe, engine or engines, accessories or equipment is functioning according to established standards while the aircraft operates in its intended environment. (U.S. Air Force photo by Senior Airman Cody Sanders)