Accident Sequence
A witness reported that the multi-engine turboprop airplane was on final approach to land when it suddenly veered to the left and entered a rapid descent. The witness heard the "whine of the engines" before the airplane impacted terrain about half a mile south of the runway threshold.
Maintenance History
In the days preceding the accident flight, the airplane had been at a maintenance facility to resolve a vibration in the rudder system while the autopilot system was engaged. A test flight completed immediately before the accident flight revealed no anomalies with the autopilot system. However, a mechanic noted anomalies with the rate gyro and recommended replacing it, but the pilot departed on the accident flight without the recommended repair having been completed.
Autopilot and Flight Controls
Examination of the autopilot annunciator panel indicated that the autopilot was likely not engaged at the time of impact, likely because the airplane was on a short final approach for landing. Accordingly, any existing autopilot faults would not have affected the flight as the autopilot system was likely not in use. No failures were identified with the primary flight controls, engines, or propellers that would have prevented the pilot from maintaining control of the airplane manually.
Toxicology
Toxicological testing revealed the presence of Zolpidem (the trade name for Ambien, used for short-term treatment of insomnia) in the pilot's blood; however, the reported levels would likely not have resulted in any impairment.
Probable Cause
The official probable cause is the pilot's failure to maintain airplane control during final approach.