Manufactured in 1977 it was modified by Sierra Industries, Ltd., of Uvalde, Texas, USA, in 2000. They offer a modification package named Sierra FJ44 Eagle II. This includes the replacement of the Pratt & Whitney JT15D engines by Williams FJ44 engines. Options are wing modification for faster cruise and greater range, state-of-the-art avionics and refurbishment.
N501GS has been reregistered to N15FJ in 2003 and to N449DT in 2004.