United Air Lines Flight 521 was a scheduled passenger flight operated by a Douglas DC-4 from LaGuardia Airport in New York City to Cleveland, Ohio. On May 29, 1947, while attempting to take off on runway 18, the aircraft failed to get airborne, overran the end of the runway, ripped through an airport fence onto traffic on the Grand Central Parkway, and slammed into an embankment, ultimately plunging into a pond and exploding. Ten people escaped the flaming wreckage; only five of them survived.