A crew works atop exhaust cooler 1 of the Aeropropulsion Systems Test Facility at Arnold Air Force Base, Tenn., Sept. 14, 2021. A section of the ducting was cut away to allow heat exchangers to be installed in the cooler, as part of the Next Generation Turbine Engine Test Capability project. A hatch will be installed to allow access for future maintenance. (U.S. Air Force photo by Jill Pickett)