Accident Overview
On a flight returning to the float-plane base (CEN9) in Yellowknife, Northwest Territories, along the western shore of Great Slave Lake, a de Havilland DHC-6-300 Twin Otter (registration C-GARW, serial number 367) equipped with floats was landing. The aircraft carried 2 crew members and 7 passengers. During touchdown, the aircraft bounced, porpoised, and landed hard on the right float. The flight crew initiated a go-around; the aircraft lifted off at low speed in a nose-high, right-wing-low attitude and continued in a right turn toward the shore. As the turn progressed, the right wing contacted power lines and cables before the float bottoms impacted the side of an office building. The aircraft then dropped to the ground on its nose and cartwheeled into an adjacent parking lot. Both crew members suffered fatal injuries; 4 passengers sustained serious injuries, and 3 passengers had minor injuries. The aircraft was substantially damaged, and the 406 MHz emergency locator transmitter activated. No fire occurred. The accident happened at 1318 Mountain Daylight Time.
History of Flight
The crew began their duty day with a departure from CEN9 at 1058 on a 45-minute cargo flight to a mining camp at Thor Lake, Northwest Territories. C-GARW departed Thor Lake at 1248 for the return flight to CEN9 with 7 passengers, climbing to 3500 feet above sea level. The first officer acted as pilot flying from the right seat, and the captain was pilot not flying in the left seat. The crew obtained weather information from Yellowknife Airport (CYZF) automatic terminal information service and briefed their planned approach to CEN9. When joining a left base for landing, the CYZF control tower advised that winds at the airport were variable from the southwest at 10 knots, gusting to 30 knots. CEN9 is not visible from CYZF. Due to 2 to 3-foot waves on the lake, the crew planned to land close to the shore, avoiding the passage between the shore and Jolliffe Island. The captain advised maintaining airspeed above 80 knots indicated airspeed, 10 knots above the normal full-flap approach speed of 70 knots. During the approach, the captain twice cautioned the first officer about low airspeed. The aircraft touched down in the intended area, bounced, then contacted the water a second time with the right float first. The float dug in, causing the aircraft to yaw right toward the shore. The stall warning sounded for about 0.3 seconds.
Analysis
No indication of an aircraft system malfunction was found. The analysis focused on crew coordination and handling during the landing and attempted go-around. The crew briefed the approach aware of strong southerly winds and rollers, agreeing on an approach speed above 80 knots. Airspeeds prior to touchdown were at or below 80 knots, evidenced by the captain's warnings. Strong westerly winds just before touchdown created crosswind and wind shear, likely aggravated by turbulence from The Rock upwind of the touchdown zone. This combination caused airspeed fluctuations, leading to the initial hard landing and bounce as the first officer flared. After the bounce, the aircraft was in slow flight. The strong right crosswind and pilot aileron compensation likely caused the right float to contact water first during the second touchdown. The aircraft yawed right, and the nose pitched down. Aft elevator control was used to counter the nose-down movement and initiate a go-around. This, combined with the pitch-up effect of adding full power, resulted in the aircraft lifting off in a very nose-high, right-wing-low attitude. With full flaps and both wings in a stalled or semistalled condition, the aircraft could not accelerate or climb. Since the captain assumed control without declaring it, both pilots may have been manipulating controls during the go-around. By allowing the nose to continue pitching up when full power was added, airspeed could not increase, resulting in wing stall and loss of control.
Findings as to Causes and Contributing Factors
Airspeed fluctuations at touchdown, coupled with gusty wind conditions, caused a bounced landing. Improper go-around techniques during recovery from the bounced landing resulted in a loss of control. It is possible that confused crew coordination during the attempted go-around contributed to the loss of control.