Accident Summary
On an unspecified date, a four-engine airplane departed Kenneth Ingalls Sawyer Air Force Base en route to Chicago-O'Hare International Airport. The aircraft carried 23 passengers and a crew of four. After being cleared to descend from 22,000 feet to 8,000 feet, the crew reduced speed. At an altitude of 13,700 feet and a speed of 313 knots, an in-flight explosion occurred.
The explosion caused both wings to detach, all four engines to separate, and the horizontal and vertical stabilizers to break away. Out of control, the airplane dove into the ground and crashed in an open field near Greenwood, approximately 37 miles northwest of Chicago-O'Hare. The aircraft was totally destroyed, and all 27 occupants perished.
Investigation
Investigators were unable to determine the exact cause of the accident with certainty. The most probable scenario identified was an over-pressurization event beneath the cargo floor, an area that housed fuel tanks and other potential sources of ignition. An explosion caused by the ignition of accumulated combustible vapors in that area could rapidly propagate to adjacent fuel-containing zones.
Strong evidence indicated explosive over-pressures in the forward, aft, and upper fuel tank areas. The investigation noted that if the walls or fittings of the rubber bladder cells containing fuel were to fail, fuel or vapor could be released into the tank cavity and subsequently migrate to other parts of the aircraft.
Probable Cause
The official probable cause states that the exact cause could not be determined with certainty. Considered as 'most probable' was an over-pressurization under the cargo floor, an area that houses fuel and other potential sources of ignition. An explosion caused by the ignition of accumulated combustible vapors occurring in that area could rapidly propagate to adjacent areas where fuel is present. There was also 'strong evidence' of explosive over-pressures in the forward, aft and upper fuel tank areas. Significantly, investigation showed that were the walls or fittings of the rubber bladder cells containing the volatile liquid to fail, fuel or vapor could be released into the tank cavity and in turn migrate to other parts of the aircraft.