Airman Jack Gagnon reads instructions to Airman Joseph Rhym, 364th Training Squadron electrical and environmental systems apprentice course students, as they work in the flight deck of an F-15 Eagle at Sheppard Air Force Base, Texas, Oct. 5, 2018. Gagnon and Rhym are working on replacing an oxygen regulator. For training, they will remove and replace the component multiple times in the week, but on the operational side the regulator is usually replaced every six months. (U.S. Air Force photo by Airman 1st Class Pedro Tenorio)