Civil Aeronautics Board report into the crash of United flight 21 on 4 December 1940.
Civil Aeronautics Board, US Department of Commerce
after 1940 <div style="display: none;">date QS:P,+1940-00-00T00:00:00Z/7,P1319,+1940-00-00T00:00:00Z/9</div>
US Department of Transportation Special Collection <a rel="nofollow" class="external autonumber" href="http://specialcollection.dotlibrary.dot.gov/Document?db=DOT-AIRPLANEACCIDENTS&amp;query=(select+92)">[1]</a>