Staff Sgt. Cody Carlson (left) and Airman 1st Class Colby Mercil, Crew Chiefs assigned to U.S. Air Force aircraft 80104, a KC-135R Stratotanker, prepare to tighten a lug nut with a torque wrench while installing a new nose gear tire on April 10, 2012. Staff Sgt. Carlson, from Sandwich, Ill., is a Guardsman assgned to the 126th Maintenance Squadron while Airman Mercil, from Colorado Springs, Col., is assigned to the 906th Air Refueling Squadron, an active duty Air Force unit that is associated with the 126th Air Refueling Wing, Illinois National Guard, at Scot AFB, Ill. Crew chiefs perform and oversee everyday maintenance to aircraft. They recover and inspect aircraft after a flight, change tires and brakes, service engine oil and hydraulic fluid, and execute numerous inspections. They ensure an aircraft is safe and reliable. (National Guard photo by Master Sgt. Ken Stephens)