THC was the prime factor.
The TSB’s Analysis
The TSB determined the airplane and its systems were working properly before the crash. What follows is from the TSB analysis of the incident:
When C-GATV departed for Lutsel K'e, the weather at Yellowknife was marginal for VFR flight. Low clouds persisted for the entire flight, which was flown at low level so the pilot could maintain visual contact with the ground. The descent during the last 2 min. of the flight suggests that the ceiling had become lower.
The conduct of the flight and the nature of the impact were characteristic of a CFIT event: the aircraft struck rising terrain under the pilot's control at cruise speed, with a wings-level attitude and a heading generally consistent with the direct track to the destination. Because no effective evasive maneuvers were made before impact, it is likely that the crest of the Pehtei Peninsula was obscured in fog and not visible to the pilot. The application of increased engine power immediately before impact was likely made when the terrain in front of the aircraft suddenly became visible.
When the pilot transmitted a position report 6 nm closer to Lutsel K'e than the actual position, it is possible that he believed that the shoreline of Great Slave Lake had been crossed and that open water at about 500 ft. ASL lay ahead. Since GPS was likely the primary navigational aide, there should have been little ambiguity in position, unless the unit was set to a waypoint associated with the RNAV approach at Lutsel K'e. However, the location of the site and the wreckage trail track indicate that the aircraft was proceeding directly to the airport. If an instrument approach had been planned, the aircraft should have been navigating toward a waypoint associated with the approach, and at an altitude no lower than 3,100 ft. in accordance with the company-published route.
A TAWS installation in C-GATV could have warned of the impending collision with the ground, possibly in sufficient time to prevent the accident.
Investigators could not determine why the pilot chose to fly the trip under VFR. Conditions were suitable to enable operation under IFR at altitudes providing safe terrain clearance. The pilot, the aircraft and the company were qualified to operate the trip under IFR. The en route weather was suitable, and with the freezing level well above the minimum IFR route altitude, icing was not a factor to preclude IFR flight. The cloud base was above the minimums required for successful completion of an approach and landing at Lutsel K'e. Before departure, the forecast weather was such that Yellowknife could be filed as an IFR alternate.
The fuel load was not considered to be a factor in the pilot's decision to fly the trip under VFR rather than IFR. Fuel was readily available at Yellowknife, and there was adequate time between the arrival from Fort Simpson and the departure for Lutsel K'e to bring the fuel quantity to IFR requirements under the supervision of dispatch personnel.
Although the pilot had gained experience in an IFR environment during his flying as a copilot in multiengine aircraft, he had limited experience in single-pilot IFR operations. This may have led to reluctance to file an IFR flight plan on the accident flight, and the decision to remain visual in marginal VFR weather conditions. The route lay mostly in uncontrolled airspace, and when flight visibility deteriorated, the pilot had the option of climbing without ATC clearance to a safe altitude, and conducting an instrument approach at Lutsel K'e. The pilot apparently was willing to fly in cloud as indicated by the earlier flight from Fort Simpson to Yellowknife, albeit on a VFR flight plan in controlled airspace.