1937 Civil airways of the United States as designated in Civil Air Regulations - chapter 60, by the U.S. Department of Commerce, Bureau of Air Commerce, from the Digital Commonwealth - commonwealth 0z709330j. (<a rel="nofollow" class="external free" href="https://www.digitalcommonwealth.org/search/commonwealth:0z709330j">https://www.digitalcommonwealth.org/search/commonwealth:0z709330j</a>)
U.S. Department of Commerce, Bureau of Air Commerce
Digital Commonwealth