Civil Aeronautics Board report into the crash of United Flight 16 on 4 November 1940.
Civil Aeronautics Board, US Department of Commerce
US Department of Transportation Special Collections <a rel="nofollow" class="external autonumber" href="http://specialcollection.dotlibrary.dot.gov/Document?db=DOT-AIRPLANEACCIDENTS&amp;query=(select+91)">[1]</a>