Rachel Garrard, a test manager with the Propulsion Test Branch of Arnold Engineering Development Complex (AEDC), explains how the C-1 altitude engine test cell works to Maj. Gen. Evan Dertien, commander, Air Force Test Center, during Dertien's visit to Arnold Air Force Base, headquarters of AEDC, Oct. 13, 2021. In C-1, large military and commercial engines are tested at simulated altitude conditions. In recent years, C-1 has primarily been used to test F119 engines for the F-22 Raptor and the F135 engines for the F-35 Lightning II. (U.S. Air Force photo by Jill Pickett)