Staff Sgt. Cody Carlson, a Crew Chief assigned to U.S. Air Force aircraft 80104, a KC-135R Stratotanker, assists with replacing bearings in a new nose gear tire before installing it on April 10, 2012. Staff Sgt. Carlson, from Sandwich, Ill., is assigned to the 126th Maintenance Squadron, a unit 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)