On September 1, 1961, at 02:05 CDT, the flight crashed into a field south of Clarendon Hills, IL shortly after takeoff from Midway Airport (ICAO: KMDW) in Chicago, killing all 73 passengers and five crew on board; it was at the time the deadliest single plane disaster in U.S.

[1][2] The accident was investigated by the Civil Aeronautics Board, which concluded its probable cause was the loss of a 5/16 inch bolt which fell out of the elevator control mechanism during the climb from Chicago, resulting in an abrupt pitch up followed by a stall and crash.

[3][4] The four-engine propliner originated in Boston, and after making intermediate stops in New York and Pittsburgh, arrived at Chicago Midway Airport at 01:18 CDT, where a new crew took over, and fuel and oil were added.

[3] The CAB investigated the accident, and as the wreckage pieces were reassembled and scrutinized, it became apparent that a critical 5/16 inch AN-175-21 nickel steel bolt was missing in the elevator boost linkage mechanism.

"[4] As a result of their investigation of the accident, the CAB urged the FAA to mandate a redesign of the elevator boost control, so that the shift to manual mode could be easily carried out by the pilots, even when applying nose down pressure.