Accident Details
On the evening of the accident, a float-equipped, turbine-engine DHC-3 Otter departed Tasu, British Columbia, at about 1940 Pacific daylight saving time (PDT) on a charter visual flight rules (VFR) flight to Alliford Bay, 26 nautical miles to the north. The pilot and two passengers were on board. The aircraft did not arrive at its destination, prompting the operator to initiate a search. The wreckage was located the following day, 18 nautical miles south of Alliford Bay, in rugged terrain at an elevation of 1,700 feet above sea level (asl). The aircraft was destroyed, and there were no survivors.
Flight History and Weather Information
The aircraft had departed Alliford Bay earlier at 1836 PDT to pick up two passengers at Tasu, on the south end of Newcombe Inlet. As was informal practice, the Harbour Air flight dispatcher called the Sewell Inlet logging camp, located about two-thirds of the way along the route, for weather information. There was no weather reporting station at Sewell Inlet; the dispatcher was advised by an employee at the campsite that there was light drizzle and restricted visibility due to fog. The 2000 PDT Environment Canada report for Sandspit airport, 6 nm east of Alliford Bay, indicated scattered clouds at 900 feet and 2,800 feet, an estimated broken ceiling at 4,700 feet, overcast at 10,000 feet, visibility 15 miles in light rain showers, temperature 14°C, dewpoint 11°C, wind 240° magnetic at 6 knots, and altimeter 29.86 inches of mercury.
Witness Observations and Flight Path
A witness reported seeing the Otter flying north from Newcombe Inlet into the valley where it was later found. At the witness's position, 4 nm south of the accident site, a heavy rain shower lasting several minutes had diminished to light drizzle when the aircraft flew overhead. The witness could not estimate ceiling or cloud cover. The pilot's planned route was to head north from Tasu to the north end of Newcombe Inlet, cross low terrain for about two miles, then turn east through a valley to Sewell Inlet en route to Alliford Bay. Just north of the turn-off to Sewell Inlet, another valley leads northward into a box canyon where terrain rises abruptly to 3,350 feet asl. The two valleys are similar in appearance, both with a creek and road following the floor. The aircraft flew past the Sewell Inlet valley, continued north into the box canyon valley, and struck the side of the valley at 1,700 feet asl.
Wreckage and Engine Examination
Wreckage damage and impact scars indicated the aircraft was in controlled, wings-level flight on a heading of about 210° magnetic when it struck the ground. Evidence showed the engine was delivering power, and impact speed was estimated at about 80 miles per hour. The Pratt & Whitney PT6 A-135 turbine engine was examined at the manufacturer's facility in Montreal; it was concluded that the engine was operational at impact and capable of producing maximum rated power, though the power setting at impact was not established.
Investigation Findings
The aircraft was certified, equipped, and maintained in accordance with regulations and approved procedures. Weight and center of gravity were within prescribed limits. No pre-impact mechanical or structural failure was found. The pilot was qualified for the flight, and no evidence of physiological factors affecting performance was identified.
Probable Cause
The pilot probably made a navigational error because of restricted visibility in fog and light drizzle and inadvertently entered the valley to the north rather than turning east toward Sewell Inlet. The aircraft heading at impact, 150 degrees off the required heading, indicates the pilot had turned around, likely either recognizing he was in the wrong valley or beginning to encounter adverse weather. Because the aircraft struck in a wings-level attitude with no last-second evasive maneuvering, it is likely the pilot's forward visibility was restricted and he did not see the ground in time to avoid impact. If the weather observed by the witness prevailed in the valley, the aircraft likely entered clouds before reaching 1,700 feet. Once in cloud, the pilot would have had no option but to climb to avoid high terrain. It is probable that the pilot delayed his decision to reverse course until unable to avoid the weather.
Causes and Contributing Factors
The pilot probably made a navigational error because of restricted visibility in fog and light drizzle and entered the wrong valley, and he delayed his decision to reverse course until he was unable to avoid the weather.