On March 28, 2000, about 1708 Pacific standard time, an Airbus A300-600, N667FE, registered to First Security Bank, and operated by Federal Express, Inc, a Title 14 CFR 121 supplemental cargo flight, declared an emergency due to smoke in the cockpit while on approach to Seattle-Tacoma International Airport, Seattle, Washington (the aircraft's scheduled destination). Shortly after declaring the emergency, the aircraft landed without further incident. Visual meteorological conditions prevailed and an instrument flight plan was filed. The airline transport pilot-in-command and first officer were uninjured. The flight originated from Indianapolis, Indiana, about 4 hours prior to the incident. Maintenance personnel from Federal Express reported that a post flight inspection of the aircraft revealed a significant oil leak originating from the auxiliary power unit (APU). They also reported that the oil leaking from the APU had contaminated the environmental system resulting in smoke in the cockpit.