By | April 21, 2010
U.S. Air Force Staff Sgt. Mark Graveline operates an aircraft auxiliary power unit on the flightline at Joint Base Charleston, S.C., prior to a C-17 mission to North Auxiliary Airfield in North, S.C., April 7, 2010. The power units are utilized to perform preflight checks on an aircraft before engine startup, reducing wear and tear on the aircraft's auxiliary power unit and also saving fuel. Sergeant Graveline is an aircraft crew chief with the 315th Aircraft Maintenance Squadron. (U.S. Air Force photo/Tech Sgt. Jacob Bailey)