Senior Airman Kymric Walker, 28th Maintenance Squadron aerospace propulsion technician, ties a safety wire onto a B-1 engine during a preposition spare engine inspection in the propulsion back shop at Ellsworth Air Force Base, S.D., Oct. 17, 2013. Propulsion Airmen perform maintenance and repairs to ensure the efficiency and functionality of engines before they are installed into a B-1. (U.S. Air Force photo by Airman 1st Class Rebecca Imwalle/ Released)