The NASA Langley Research Center received authorization from NASA Headquarters on September 18, 2017 to acquire three excess C-20B Gulfstream III aircraft from the U.S. Air Force. Two of these aircraft are used as parts support for the Agency, and the third aircraft is used for research. The research G-III (C-20B) aircraft, designated NASA 520, replaced the Dassault HU-25A Guardian aircraft (NASA 524). The research aircraft arrived at NASA Langley on December 7, 2017. NASA Langley has installed the following features:  an engine hush kit; research power distribution system; intercom system; dropsonde capability; and, two nadir portals in the fuselage. The hush kit enables the aircraft to be Stage III noise compliant, allowing the aircraft to deploy nationwide and worldwide without requiring engine noise waivers. The nadir portals allow the aircraft to install earth science sensors, as is possible with the Center’s B200 King Air aircraft, NASA 529.