What happened
While operating at 12,000 feet above the freezing level, the flight received clearance to descend to an altitude of 9,000 feet. Shortly after beginning this descent, the crew issued a mayday emergency call. Following this transmission, all radio and radar communication with the aircraft ceased.
Radar tracking indicated that the aircraft entered a left-hand descending maneuver during its descent. During this period, the left outboard wing panel and both engines detached from the airframe while still in flight. The final transponder signal was recorded at an altitude of 2,800 feet. The aircraft eventually struck the ground following a near-vertical descent. All eight occupants were killed in the accident.
Findings
Investigation of the wreckage revealed that the left wing panel had detached due to positive structural overload. No evidence of fatigue or pre-existing cracks was identified at the fracture sites. Investigators also noted damage on the inboard cowling of the left engine that corresponded with damage found on both the vertical and right horizontal stabilizers, though the exact sequence of these failures could not be confirmed.
An NTSB trajectory analysis determined that the in-flight separation occurred at roughly 5,600 feet while the aircraft was traveling southeast in a steep dive between 50 and 70 degrees. Additionally, the elevation trim indicator was discovered in a full nose-up position. The investigation concluded that the structural failure involved the wing and engine cowlings exceeding their design stress limits.