Accident
At approximately 1235 Pacific daylight time, a Liard Air Limited de Havilland DHC-6-100 Twin Otter (registration C-FAWC, serial number 108) was taking off from a gravel airstrip near the Northern Rockies Lodge at Muncho Lake, British Columbia. The flight was a visual flight rules (VFR) flight destined for Prince George, British Columbia. After becoming airborne, the aircraft entered a right turn. During the turn, the right outboard flap hanger contacted the Alaska Highway. The aircraft subsequently struck a telephone pole and a telephone cable, impacted the edge of the highway a second time, and crashed onto a rocky embankment adjacent to a dry creek channel. The aircraft came to rest upright approximately 600 feet from the departure end of the airstrip. An intense post-impact fire ensued, and the aircraft was destroyed.
Injuries
One passenger suffered fatal burn injuries. One pilot was seriously burned, and the other pilot sustained serious impact injuries. The remaining two passengers received minor injuries.
Probable Cause
The investigation identified the following causes and contributing factors: 1. The takeoff was attempted at an aircraft weight that did not meet the performance capabilities to clear an obstacle, resulting in the aircraft striking a telephone pole and cable during initial climb. 2. A takeoff and climb to 50 feet performance calculation was not completed prior to takeoff, leaving the flight crew unaware of the distance required to clear the telephone cable. 3. The southeast end of the airstrip was not clearly marked, so the takeoff was initiated with approximately 86 feet of usable airstrip behind the aircraft. 4. The takeoff was attempted in an upslope direction and in a light tailwind, both of which increased the distance necessary to clear obstacles.
The investigation also noted risks: 1. Operational control within the company was insufficient to reduce risks associated with takeoffs from the lodge airstrip. 2. Takeoff weight limits for lodge airstrip operations were not effectively communicated to the flight crew. 3. Maximum performance short takeoff and landing (MPS) techniques may have been necessary, but neither the aircraft nor the company were approved for MPS operations. 4. The first officer’s shoulder harness assembly had been weakened by age and ultraviolet light exposure, causing it to fail within design limits at impact. 5. The SeeGee calculator operating index values used by Liard Air Twin Otter pilots were 0.5 to 1.0 units greater than correct values, resulting in actual center of gravity being forward of calculated. 6. No airworthiness standards specifically intended to contain fuel or prevent fuel ignition in crash conditions exist for fixed-gear aircraft under US Civil Aviation Regulation 3 and Federal Aviation Regulation 23.