High Quality Content by WIKIPEDIA articles! 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. The tower controllers on duty that day at National testified that the P-38 had taken off on Runway 3, turned left north of The Pentagon, circled over Arlington, then returned, requesting permission to land due to engine trouble. The controller cleared the aircraft to join the left traffic pattern, but instead it flew south of the airport and entered a long straight-in approach at the same time Flight 537 was turning onto a shorter final.