Ever wonder what aircraft maintenance looked like in the late 1930s? Here, mechanics are working on the engines of a Douglas DC-3 Mainliner during the aircraft’s routine visit to United’s Cheyenne, Wyoming, maintenance base. Image: United Air Lines, Cheyenne, Wyoming, Douglas DC-3, late 1930s. Gift of United Airlines Archives. 1999.047.243 This image was posted on April 13, 2020.