The ARJ-21 uses a variant of an engine which first ran in 1982, (the ARJ-21 variant first ran in 2007) while the 717 had a new engine of which the basic version first ran in 1995, & the variant in the 717 first ran in 1997.Eventough using MD-80/Boeing 717 desain, ARJ-21 claim to be provide more economics costs per seat due to better engine and construction materials.