U.S. Air Force Staff Sgt. Kritopher Castillo, a 927th Aircraft Maintenance Squadron crew chief, calls on the radio to a KC-135 Stratotanker air crew during a pre-flight inspection during a unit training assembly on MacDill Air Force Base, Fla. Prior to flight, the crew chief stands outside the aircraft, observing aircraft functions for safety prior to departure. (U.S. Air Force photo by Staff Sgt. Brad Tipton)