Airman 1st Class Allison Freeman, 82nd Aerospace Medicine Squadron aerospace and operational physiology technician, assists a Euro-NATO Joint Jet Pilot Training student with his oxygen mask prior to an altitude chamber flight June 8, 2012 at Sheppard Air Force Base, Texas. Undergraduate Pilot Training students are exposed to low-pressure altitude flights to experience the onset of hypoxia, or a lack of oxygen to the blood and brain, as part of the physiology training required of all military aviators. (U.S. Air Force photo/Dan Hawkins)