Airman 1st Class Alexander Prevost, 92nd Aircraft Maintenance Squadron crew chief, installs the boom sighting window of a KC-135 Stratotanker at Fairchild Air Force Base, Wash., Sept. 25, 2013. Cleaning the boom sighting window is part of the preflight inspection, which is required prior to flight. (U.S. Air Force photo/Airman 1st Class Janelle Patiño)