Passenger Account
A surviving passenger aboard the aircraft stated that after takeoff, the aircraft banked steeply to the left and shuddered. The passenger observed the pilot reaching for the flap control handle and recalled hearing a warning horn sounding in the background.
Witness Observations
Multiple witnesses on the ground reported that the aircraft's speed and rate of climb appeared slow following departure. They also noted the aircraft wobbling and dipping its wings. One witness, positioned in line with the takeoff path, saw the flaps being retracted slightly.
Wreckage Examination
Examination of the wreckage disclosed that the flap jackscrew was extended by 10 threads, measuring 1.66 inches, which corresponds to approximately 14 degrees of flaps down. The manufacturer recommends taking off with either flaps up or at the 1/4 (7.5 degrees) down setting.
Pilot Procedure
It was known that the pilot had a habit of beginning the takeoff roll with the flaps up. As liftoff speed was attained, the pilot would 'slap' the flap handle down to the detent, which is the 1/4 or 7.5-degree flaps setting.
Experimentation
Subsequent experimentation demonstrated that it was possible to inadvertently slap the flap handle past the detent to the full down position.