![Boeing Model 40-B4 mail plane at Boeing factory, August 24, 1929 - Museum of History and Industry - University of Washington Digital Collections Boeing Model 40-B4 mail plane at Boeing factory, August 24, 1929 - Museum of History and Industry - University of Washington Digital Collections](https://digitalcollections.lib.washington.edu/digital/iiif/imlsmohai/4322/full/full/0/default.jpg)
Boeing Model 40-B4 mail plane at Boeing factory, August 24, 1929 - Museum of History and Industry - University of Washington Digital Collections
![Boeing Model 40-B4 biplane at Boeing plant, Seattle, September 26, 1929 - Museum of History and Industry - University of Washington Digital Collections Boeing Model 40-B4 biplane at Boeing plant, Seattle, September 26, 1929 - Museum of History and Industry - University of Washington Digital Collections](https://digitalcollections.lib.washington.edu/digital/iiif/imlsmohai/8461/full/full/0/default.jpg)
Boeing Model 40-B4 biplane at Boeing plant, Seattle, September 26, 1929 - Museum of History and Industry - University of Washington Digital Collections
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