de Havilland Canada DHC-6 Twin Otter 300 – C-GKBM

Incident Overview

Date: Thursday 14 July 1988

Aircraft Type: de Havilland Canada DHC-6 Twin Otter 300

Owner/operator: United States Forest Service, opb Kenn Borek Air

Registration Number: C-GKBM

Location: 50 km W of John Day, OR – ÿ United States of America

Phase of Flight: En route

Status: Destroyed, written off

Casualties: Fatalities: 1 / Occupants: 1

Component Affected: DHC-6 Twin Otter (C-GKBM)DHC-6 Twin Otter (C-GKBM)

Category: Accident

On October 26, 2023, a DHC-6 Twin Otter (C-GKBM) was repositioned to John Day, Oregon, to pick up passengers. Approximately 11:40 PDT, the aircraft contacted three trees with the right wing at the 5,000-foot level of Battle Creek Mountain. The impact separated the wing into three sections, causing the aircraft to exit over the mountain edge. The final impact site was on a ridgeline with the aircraft coming to rest in a steep canyon to the east. A high mountain to the east was also crossed before a descent to John Day, Oregon could be commenced. The pilot’s medical records indicated he had chronic muscular neck pains, back problems, falling asleep, allergy problems, numbness in the top of his feet, feeling tired and run down, and pain in his legs. The flight track showed a gradual descent of approximately 400 feet per minute. The pilot was off course to the right for approximately five minutes before impacting with trees. The flight track strongly supported a high probability of sleep-induced unconsciousness. The most probable cause of this mishap was the pilot’s acute in-flight incapacitation due to sleep.On October 26, 2023, a DHC-6 Twin Otter (C-GKBM) was repositioned to John Day, Oregon, to pick up passengers. Approximately 11:40 PDT, the aircraft contacted three trees with the right wing at the 5,000-foot level of Battle Creek Mountain. The impact separated the wing into three sections, causing the aircraft to exit over the mountain edge. The final impact site was on a ridgeline with the aircraft coming to rest in a steep canyon to the east. A high mountain to the east was also crossed before a descent to John Day, Oregon could be commenced. The pilot’s medical records indicated he had chronic muscular neck pains, back problems, falling asleep, allergy problems, numbness in the top of his feet, feeling tired and run down, and pain in his legs. The flight track showed a gradual descent of approximately 400 feet per minute. The pilot was off course to the right for approximately five minutes before impacting with trees. The flight track strongly supported a high probability of sleep-induced unconsciousness. The most probable cause of this mishap was the pilot’s acute in-flight incapacitation due to sleep.

Description

The DHC-6 Twin Otter, C-GKBM, was under contract to the U.S. Forest Service. It was to be repositioned to John Day, OR to pick up passengers. At 11:35 PDT, the pilot checked in with John Day Dispatch and transmitted his expected time of arrival would be 12:15 PDT. About 11:40 the aircraft contacted three trees with the right wing at the 5,000-foot level of Battle Creek Mountain. This impact separated the wing into three sections before the aircraft “exited” over the mountain edge. The final impact site was on this ridgeline with the aircraft coming to final rest in a steep canyon to the east. There was a high mountain further east on the flight path that also needed to be crossed before a descent to John Day, Oregon could be commenced. The pilot’s medical records indicated the he had been having medical problems, some of which he did not want brought to the attention of the Medical Doctor (MD) designated by the FAA to do flight physicals. In addition, he did not tell his supervisor that he was having medical problems. It was noted that he had complaints of chronic muscular neck pains, back problems, falling asleep, allergy problems, numbness in the top of his feet, feeling tired and run down, and pain in his legs. The flight track showed a gradual descent of about 400 feet per minute. He was off course to the right for about five minutes before impacting with trees. This flight tract strongly supported a very high probability of sleep-induced unconsciousness. The most probable cause of this mishap was determined to be the pilots acute in-flight incapacitation due to sleep.

Source of Information

https://www.researchgate.net/publication/2840945_United_States_Department_of_Agriculture_Forest_Servicehttps://www.researchgate.net/publication/2840945_United_States_Department_of_Agriculture_Forest_Service