What happened
During a departure from a remote lake, a float-equipped aircraft was climbing through approximately 150 feet when the flight crew encountered significant weather disturbances. The flight conditions at the time included rain, turbulence, and winds of 20 knots. While performing a left turn, the pilot encountered a severe gust of wind. At the same moment, the pilot moved the flap lever to the 'UP' position, though the manual pump handle had not yet been operated to retract the flaps.
As the aircraft entered a left turn that increased to a bank angle of nearly 90 degrees, the plane entered a stall. During the subsequent descent, the left wing struck the surface of the lake. The impact was severe enough to tear the left wing from the fuselage and crush the floats upward. There were four fatalities resulting from the accident.
Findings
Post-accident inspections of the wreckage revealed that the right aileron and the right wing flap were positioned in an intermediate state. The aircraft's flap system utilizes a double-acting cylinder and a common torque tube to actuate both flaps. Investigators noted that the pilot had expressed concerns regarding the possibility that the flaps might have retracted without the use of the manual pump.
Upon recovery of the aircraft, an examination of the ratchet valve assembly and the hydraulic system showed evidence of air and hydraulic fluid leakage. However, subsequent testing of the ratchet valve at an overhaul facility did not replicate these leakage findings.