Overview
The accident occurred during a descent from 12,000 feet after the flight was cleared to maintain 9,000 feet. About 1-1/2 minutes after the clearance, the crew declared a mayday emergency. Radio and radar contact were subsequently lost. The aircraft crashed in a near-vertical descent. Radar data indicated that after starting the descent, the aircraft entered a left descending maneuver. The last transponder reply was received at 2,800 feet.
Inflight Breakup
During the descent, the left outboard wing panel and both engines separated from the aircraft while still in flight. The National Transportation Safety Board (NTSB) trajectory study determined that the inflight separation occurred at approximately 5,600 feet. At that time, the aircraft was heading southeast in a dive angle between 50 and 70 degrees. The separated wing panel and parts of the engine cowling were found about 3/4 mile from the main wreckage.
Wreckage Examination
Examination of the separated left wing panel revealed that it had failed due to positive overload. No evidence of fatigue or pre-existing cracks was found at any fracture area. Damage was observed on the left engine's inboard cowling that matched damage on the vertical stabilizer and the right horizontal stabilizer; however, the sequence of cowling separation could not be verified. The elevation trim indicator was found with a full nose-up indication. Both pilots were instrument rated. All eight occupants were killed in the accident.
Probable Cause
The official findings listed three occurrences. The first was loss of control in flight, with the reason for the occurrence undetermined. The second was an airframe/component/system failure/malfunction, including wing overload, exceeded design stress limits of the aircraft, wing separation, and cowling separation. The third was in-flight collision with terrain/water during an uncontrolled descent.