Background
On the day of the accident, three Whistler Air Services Ltd. floatplanes were conducting 20-minute sightseeing flights over the Whistler area of British Columbia. The aircraft operated from the company dock at the south end of Green Lake, approximately three kilometres north of Whistler Village. The accident aircraft, a Cessna 185 floatplane (serial number 18502823), was piloted by a commercially licensed pilot and carried four adult passengers.
Pre-flight and Loading
Before boarding the passengers, the pilot fuelled the aircraft and pumped about 30 litres of water from two compartments of the left float that were known to leak. The floats each contained eight compartments designed to be independent, but water often migrated between adjacent compartments. The aircraft was estimated to weigh 3,280 pounds at departure, 40 pounds below the maximum gross weight of 3,320 pounds. The centre of gravity was calculated at 45.0 inches aft of the datum, within the allowable range of 41.9 to 46.5 inches.
The Flight
After departing the dock, the floatplane taxied northeast for approximately 4,500 feet before turning to begin a take-off run to the southwest. During the taxi, the pilot instructed passengers on exiting procedures and life jacket locations. The take-off run was made with wind about 20 degrees left of the nose. The engine developed correct manifold pressure and maximum rpm without unusual noises. However, the floatplane did not accelerate normally, and the take-off run was longer than usual.
Shortly after becoming airborne, the pilot noted lower-than-normal airspeed. At about 1853 Pacific daylight time, the floatplane lifted off but remained low over the lake surface. Approaching the end of the lake, the pilot turned right to avoid trees. A second right turn was made to avoid the shoreline, during which the floatplane abruptly descended and struck the water. The height during the brief flight did not exceed 50 feet, and the stall warning horn sounded intermittently.
Impact and Rescue
Upon impact, both floats broke off, and the aircraft sank in a wings-level, nose-down attitude in about 15 feet of water. The pilot opened both cabin doors and dived three times to assist the passengers. All five occupants escaped, though some reported that headset cords and heavy clothing hindered egress. A nearby boat rescued all occupants immediately.
Investigation Findings
Examination of the aircraft after recovery revealed the flap handle in the fully retracted position and the wing flaps fully retracted (0 degrees). The pilot had initially selected flaps to 20 degrees for take-off and recalled reducing them to 10 degrees during the flight. The pilot's operating handbook recommended 20 degrees of flaps for take-off and cautioned against retraction until reaching a safe altitude and airspeed.
The stall speed at the estimated weight was 50 KIAS with 20 degrees flap and 0 degrees bank, and 55 KIAS with flaps retracted. At a 30-degree bank, the stall speed increased to 59 KIAS. The two right turns would have increased the stall speed due to bank angle, and retracting the flaps further raised the stall speed, reducing the margin above stall.
The aircraft likely experienced degraded performance due to its near-maximum weight and potential water ingress into the floats. The long taxi and known leaks made additional water weight probable. The pilot's adjustments to the propeller control may have exacerbated the situation. The engine was developing power, as evidenced by propeller damage, and no pre-existing engine abnormalities were found.
Probable Cause
The investigation determined that the accident was caused by the take-off being attempted with the floatplane near its maximum allowable weight and balance and with a flap setting that adversely affected take-off performance; the floatplane's performance was insufficient to climb and clear obstacles, particularly after turning downwind; and the aircraft was at or near stall speed throughout the flight, culminating in a stall during the second turn at a height too low for recovery.