Background
The aircraft, a de Havilland DHC-3 Otter owned by Deraps Aviation Inc., registration C-FLGA, serial number 279, was operated by a pilot who held a commercial pilot licence since May 1990. He had accumulated approximately 7,980 hours of flying time, with nearly 7,800 hours on aircraft equipped with floats or skis. In recent years, he primarily flew the DHC-3 Otter and served as the company's chief pilot, responsible for professional standards.
Flight
On the day of the accident, the aircraft departed from Lake de l'Avion, Quebec, near Natashquan Airport, at approximately 1050 Eastern Daylight Time. The flight was bound for a hunting camp located 57 miles north along the Aguanish River. On board were the pilot and three passengers. The take-off weight was within prescribed limits, and the aircraft was equipped and maintained in accordance with existing regulations.
For the first 40 nautical miles, weather conditions allowed a direct course. However, thereafter, clouds frequently descended to mountaintop level, compelling the pilot to make detours. Winds were calm. According to Environment Canada, weather at Natashquan Airport improved from 1018 to 1143, with the cloud base rising from 600 to 5,500 feet above ground level. Winds were light (4–6 knots), visibility remained at least 8 statute miles, but the report noted that in mountainous terrain, clouds could linger.
Accident Sequence
Upon arriving near the destination at approximately 1135, the pilot flew over the camp to assess the landing area. He noticed moose tracks on the bank and initiated a left turn to show the passengers. The turn was performed at about 95 mph. The pilot perceived that during the turn, while close to the mountain, the aircraft drifted toward it. After completing nearly 360 degrees, he felt vibrations he attributed to wake turbulence. Sensing the aircraft sinking, he applied full power. The left wing then struck the tops of several trees, and the aircraft flipped before crashing upside down on the mountain slope.
The aircraft cut a 460-foot-long swath through trees along a constant left curve. Initially only treetops were impacted, but then the aircraft dropped rapidly, cutting trees progressively closer to the ground. The left wing tore off, contributing to the aircraft flipping due to lift asymmetry. The right wing showed little damage. Pieces of aircraft, including a pitot tube from the left wingtip, were found at the beginning of the impact path.
Investigation
The aircraft was equipped with an Apollo GPS model 360, which stored data from the last five flights. Analysis of the final flight showed a constant course for the first 32 nautical miles, then a route following the Aguanish River. The last three GPS points indicated a bank angle of 18° to 35° during the 360° turn.
The engine was producing high power at impact; the propeller had cut trees exceeding eight inches in diameter. The engine mount broke, shifting the engine rearward and rightward, pushing back the firewall and instrument panel. Passenger seat fasteners failed due to forward movement of the plywood subfloor. Cargo netting was ineffective as the aircraft was inverted at trajectory's end. Control cable continuity was maintained despite left wing separation.
The pilot reported nothing unusual about the aircraft's operation before the accident. Examination found no evidence of airframe failure or system malfunction.
Cause
Because of the geographic and weather conditions, the pilot probably had trouble judging his horizontal and vertical distance with respect to the mountain, and the aircraft crashed.