Senior Airman Zachary L. Creek and Senior Airman Brandon L. Johnson prepare to measure the gap on a C-17 Globemaster III engine proximity sensor Aug. 3, 2010, at Charleston Air Force Base, S.C. The gap is measured with a feeler gauge. Airman Creek and Airman Johnson are jet engine mechanics with the 315th Aircraft Maintenance Squadron here. (U.S. Air Force photo/Staff Sgt. Shane Ellis)