Tech. Sgt. Chris Anderson, 373rd Training Squadron, instructs students how to check for resistance on a bondage strip on a KC-135 Stratotanker, during an auxiliary power unit craftsman course at Fairchild Air Force Base, Wash., on Jan. 25, 2012. Each engine is capable of producing more than 21,000 pounds of thrust and can propel the Stratotanker to more than 500 mph. (U.S. Air Force photo/Airman 1st Class Taylor Curry)