What happened
On the day of the accident, the DHC-6 Twin Otter, registered as C-GKBM, was performing a repositioning flight under contract for the U.S. Forest Service. The aircraft was traveling toward John Day, Oregon, to collect passengers. At approximately 11:35 PDT, the pilot communicated with the John Day Dispatch, providing an estimated arrival time of 12:15 PDT.
Shortly after 11:40 PDT, while flying near the 5,000-foot level of Battle Creek Mountain, the aircraft's right wing struck three trees. This collision caused the wing to break into three separate pieces as the plane moved over the mountain edge. The aircraft eventually came to a stop in a steep canyon located to the east of the ridgeline.
Findings
Investigation of the flight path revealed that the aircraft had been drifting off course to the right for roughly five minutes prior to the tree impacts. Data indicated a steady descent rate of approximately 400 feet per minute during this period.
Medical records for the pilot revealed several undisclosed health issues, including chronic neck and back pain, leg pain, numbness in the feet, and persistent fatigue. The pilot had intentionally withheld information regarding these conditions from both his supervisor and the FAA-designated medical examiner. Based on the flight track and the pilot's history of falling asleep, investigators concluded that acute in-flight incapacitation due to sleep was the primary factor in the accident. There were 0 fatalities and 0 injuries reported.