"Dulles International Airport, Chantilly, Va., 1958-63. Eero Saarinen, architect. Mobile lounges." A sort of giant rolling jetway (mostly out of frame at left) that carried passengers at Dulles from terminal to plane. The stair truck supported the gangway. 120mm color transparency by Balthazar Korab.
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Here's a cool old photo of passengers boarding a flight at Dulles Airport, probably some time in the early 1960s. If you've lived in the area for a long time, you'll remember those old gangways, when the mobile lounges would take you directly to the airplane. Don't forget to check out this post on Dulles Airport and this one with a great old promotional video from the 1960s.