U.S. Air Force Staff Sgt. Brian Heth, 1st Maintenance Squadron precision measurement equipment laboratory technician, does a safety check on the aircrew system tester at Joint Base Langley-Eustis, Va., Nov. 3, 2016. The system makes sure pilots are provided with accurate amounts of oxygen while in flight. (U.S. Air Force photo by Airman 1st Class Kaylee Dubois)