Piece together
U.S. Air Force Master Sgt. Eric Horton, right, and Tech. Sgt. Michael Griggs, 23d Component Maintenance Squadron aerospace propulsion craftsmen, attach a gear box to a GTCP-3650 auxiliary power unit (APU) Dec. 15, 2014, at Moody Air Force Base, Ga. The APU is a small gas turbine engine that provides power to the TF-34 engine on the A-10C Thunderbolt II. (U.S. Air Force photo by Senior Airman Olivia Bumpers/Released)