In the mid-70's American Airlines phased out its 747-123 services in favor of the DC-10. In 1974, N9668 was sold to NASA initially for use as a SCA (Shuttle Carrier Aircraft). It was used to test the Space Shuttle Enterprise prototype in gliding flight and then to transport the orbiters from Edwards AFB to Cape Kennedy. American briefly operated 747s again in SP form for Asian routes in the late 80's and early 90's before the MD-11 was delivered. NASA acquired N747BL from JAL in 1988 bringing the fleet to two. This example was undergoing maintenance at Evergreen in July, 1996.