Accident Summary
A pilot and three passengers were departing a remote lake in a float-equipped airplane. The pilot had positioned the hydraulic actuated flaps to 20 degrees before takeoff. After becoming airborne, at about 150 ft above the water, the pilot moved the flap lever to the 'UP' position in preparation for pumping the flaps up, but stated that he did not move the pump handle. Turbulence was present during the takeoff.
Sequence of Events
While in a left turn, the pilot encountered a severe gust at the moment he positioned the flap lever. The airplane stalled in the left turn, which steepened to almost a 90-degree bank. The airplane descended, and the left wing contacted the surface of the lake. The impact tore the left wing from the fuselage and crushed the floats upward. The right wing flap and right aileron were observed at the accident scene to be extended to an intermediate position.
Weather Conditions
The weather at the time included wind at 20 knots, turbulence, and rain. The pilot expressed concern that the flaps may have retracted without being pumped to the up position.
Post-Accident Examination
An examination of the flap system and the ratchet valve assembly was conducted after the airplane was recovered and the wings were removed. Leakage of hydraulic fluid and air was observed through the ratchet valve. However, additional testing of the ratchet valve at an overhaul facility did not reveal any leakage.
Probable Cause
The official probable cause was stated as: Failure of the pilot to maintain sufficient airspeed during the initial climb after takeoff, which resulted in an inadvertent stall and collision with the terrain (water). Turbulence was a related factor.