Accident Overview
An aircraft collided with trees and mountainous terrain at an elevation of about 9,500 feet msl. The accident site was on the lee side of a mountain, in a grassy meadow surrounded by high terrain on all sides. Approximately 100 feet in front of the aircraft, a rocky embankment sloped upward at about 30 degrees. About 100 feet behind the tail, terrain dropped off into a steep cliff sloping down about 65 degrees, with a valley about 1/4 mile wide at the base.
Wreckage and Scene
The farthest piece of debris was located 410 feet from the main wreckage site in a grove of trees, where fifteen tree disturbances were noted. The first disturbance began near the tops of trees and continued in a descending path. Much of the airframe exhibited semicircular impressions consistent with trunk diameters of the disturbed trees, and organic material transfer was evident in these impressions.
Meteorological Conditions
Analysis of meteorological data indicated that clear or scattered cloud conditions likely existed in the accident area, with visibility probably unrestricted. An extended north-northwestward/south-southeastward cloud band was located over the Sierra Nevada Mountains about 9 to 10 miles southwest through west of the accident location around the time of the accident. Winds aloft at 10,000 to 12,000 feet msl in the mountains were estimated from approximately 270 degrees at 40 to 45 knots. Additionally, moderate or greater turbulence and strong updrafts and downdrafts were reported along the pilot's route of flight.
Examination Findings
No mechanical discrepancies were found with the airframe or either engine during the postaccident examination.
Probable Cause
The official probable cause is: The pilot's encounter with a downdraft while approaching high terrain at an altitude insufficient to ensure adequate terrain or obstacle clearance.