Accident Overview
During a cruise phase of flight at 4,000 feet, the copilot declared a mayday indicating an uncontrolled spin. Radar tracking data revealed that the aircraft decelerated from 180 to 120 knots over a two-minute interval while maintaining a constant altitude. This steady altitude is consistent with the use of autopilot and autotrim, particularly in light of reported turbulence and icing conditions. Post-accident examination found the elevator trim set at approximately 13 degrees nose-up. Investigators found no evidence of any preimpact failure or malfunction in the aircraft's powerplants, structure, or systems.
Sequence of Events
The evidence suggests a scenario where the crew became inattentive after reducing power with the autopilot altitude hold engaged. When power was subsequently increased, the aircraft pitched up from a low airspeed, leading to uncontrolled flight. At the time of the mishap, the crew's duty day was approaching 11 hours.
Investigation Findings
The official probable cause findings identified the following elements: (1) loss of control in flight; (2) the pilot-in-command did not maintain proper aircraft handling; (3) fatigue from the flight and ground schedule; (4) improper use of throttle/power controls; (5) improper elevator trim setting; and (6) weather conditions including icing and turbulence. The event was categorized as a stall/spin. All five occupants were killed.
Probable Cause
The probable cause of the accident is loss of control in flight due to the pilot-in-command's failure to maintain aircraft handling, exacerbated by fatigue, improper throttle/power control, improper trim setting, and the presence of icing and turbulence.