U.S. Air Force Airman 1st Class Tessa Lyde, an aerospace ground equipment technician assigned to the 28th Maintenance Squadron, inspects the electrical system of a self-generating nitrogen servicing cart at Ellsworth Air Force Base, S.D., on Sept. 7, 2010. The use of nitrogen in B-1B Lancer aircraft tires prevents water vapor from freezing inside the tire at high altitudes.