Flight History
During an instructional flight conducted in icing conditions and instrument meteorological conditions (IMC), the pilots reported instrumentation difficulties to air traffic control. Initial reports indicated a problem with the autopilot, followed by a navigational issue, which they later stated was resolved, and finally a problem with the left side attitude indicator. After receiving clearance to their destination, the airplane entered a descending left turn that continued into a 360° descending turn. The flight ended in an inflight breakup, with wreckage scattered over 7,000 ft of wooded terrain.
Wreckage Examination
Examination of the engines revealed no anomalies that would have precluded normal operation. Control cable continuity was established from the cockpit to all flight control surfaces through multiple overload failures. The pitot-static system was examined with no blockages noted. Rotational scoring was observed on the vertical gyro and directional gyro, suggesting they were operating at the time of the accident. The left side attitude indicator showed no anomalies. Examination of the deice valves for the deicing boots revealed that the left wing deice valve did not operate. Corrosion was present in all three valves, but it could not be determined if the corrosion resulted from postimpact environmental exposure. Cockpit switch positions were compromised, so it could not be determined if the pilots were operating the deicing system at the time.
Pilot Information
The pilot in the left seat did not hold a type rating for the accident airplane model but was scheduled to attend flight training for such a rating. The pilot in the right seat, who held a flight instructor certificate, did hold a type rating for the airplane. Based on the flight plan indicating a "training flight" and the left-seat pilot's planned type rating training, it is likely the left-seat pilot was the flying pilot for most of the flight. The right-seat pilot's autopsy noted coronary artery disease, but the condition was poorly described; the accident circumstances are not consistent with sudden incapacitation. Toxicology testing identified diphenhydramine in the right-seat pilot's blood, but the level was too low to quantify, making it unlikely to have contributed. Prior to the descending turn, ATC noted the airplane was not following assigned headings and altitudes, and the pilots reported autopilot problems. They later stated they were using the right attitude indicator due to difficulties with the left side. It could not be determined if the reported difficulties were due to autopilot malfunction or pilot management, but they likely increased workload and may have diverted attention in IMC, leading to task saturation. The reported difficulties and lack of left-seat pilot rating likely increased the right-seat pilot's workload in diagnosing and maintaining control. The airplane's track data are consistent with spatial disorientation.
Probable Cause
The pilots’ loss of control in flight in freezing instrument meteorological conditions due to spatial disorientation and the cumulative effects of task saturation.