Eastern Air Lines Flight 537, registration N88727, was a Douglas DC-4 aircraft en route from Boston, Massachusetts to Washington, D.C. via intermediate points on November 1, 1949. NX-26927 was a Lockheed P-38 Lightning being test-flown for acceptance by the Government of Bolivia by Erick Rios Bridoux of the Bolivian Air Force. The two aircraft collided in mid-air at an altitude of 300 feet about half a mile southwest of the threshold of Runway 3 at Washington National Airport, killing all 55 aboard the DC-4 and seriously injuring the pilot of the P-38. At the time it was the deadliest airliner incident in United States history.^[2][3]

• http://en.wikipedia.org/wiki/Eastern Air Lines Flight 537