What aircraft was involved and where did it happen?

The accident on 1996-07-20 involved a Rivière des Prairies, Quebec, operated by Cessna U206F C-GNUG, at CA.

What was the probable cause of the accident?

The pilot lost control of the aircraft during takeoff in strong crosswinds because the 20-degree flap setting and STOL kit modifications reduced roll efficiency. The difficulty of the evacuation was further compounded by the complex cargo door mechanism and the physical interference caused by the extended flaps.

Fatal Seaplane Capsizing During Takeoff in Quebec

A Cessna U206F seaplane crashed during a takeoff attempt on a river in Quebec, resulting in four fatalities after the aircraft overturned and submerged.

What happened

A float-equipped Cessna U206F was attempting a pleasure flight from Rivière des Prairies, Quebec, to the Gouin Reservoir when it encountered heavy crosswinds. During the takeoff run on a river approximately 1,000 feet wide, the aircraft lifted from the water at a very low speed. After traveling about 1,000 feet, the plane dropped back onto the water in a nose-up attitude. As the pilot continued the takeoff, the left wing struck the surface, causing the left float to dig in and the aircraft to capsize.

As the aircraft rapidly filled with water, the pilot instructed passengers to unfasten their seatbelts and attempted to reach the rear cargo doors to facilitate an escape. While a bystander arrived to assist and managed to help a woman and a child evacuate through the front door, the pilot and the remaining three passengers were unable to escape and subsequently drowned.

The investigation

The investigation examined the aircraft's configuration, which included a Robertson STOL kit and a Flint Aero wing-tip auxiliary tank kit. These modifications are designed to increase lift but can reduce roll control efficiency. Investigators found that the aircraft was maintained according to regulations and was within weight and center of gravity limits. However, the investigation noted that the aircraft had not been updated with a specific service bulletin (SEB91-04) intended to improve the cargo door latch mechanism.

An ergonomic assessment of the double cargo door revealed that the mechanism is complex and difficult to operate under normal conditions. Specifically, when flaps are extended to 20 degrees, the forward leaf of the door can only open slightly, which obstructs the opening of the rear leaf. Furthermore, the investigation found that the passenger arrangement placed children near the exit, and the lack of life jackets being worn by the occupants contributed to the difficulty of the situation.

Findings

The pilot was unable to maintain roll control of the aircraft during takeoff due to strong crosswinds and the use of 20 degrees of flap.
The use of 20 degrees of flap, combined with the Robertson kit, limited the effectiveness of the ailerons in crosswind conditions.
The complexity of the rear cargo door mechanism and the physical obstruction caused by the extended flaps made evacuation extremely difficult.
The distribution of passengers meant that adults were not positioned to easily assist with the cargo door exit.
The occupants were not wearing life jackets at the time of the accident.
The aircraft had not been updated with the recommended service bulletin to improve the cargo door latch.