Accident Sequence
The float-equipped airplane initiated takeoff in light winds and calm water conditions. Witnesses observed the airplane achieving a steep climb with a nose-high attitude. Throughout the climb, no reduction in engine noise from takeoff power to climb power was heard. At approximately 200 feet above the water, the airplane entered a steep left bank, then rapidly rolled to the right and descended at a steep angle, impacting the water.
Aircraft Modifications
The airplane had been modified via a Short Take Off and Landing (STOL) kit. Certification flight tests for this modification determined that it eliminated aerodynamic warning cues for impending stalls, thus requiring installation of an audible stall warning system. The tests also mandated addition of a ventral fin and horizontal stabilizer finlets to meet directional stability certification. The least stable configuration identified during testing was the takeoff flap configuration during climb.
Certification Requirements
The Supplemental Type Certificate (STC) for the modification specified that both a ventral fin and an audible stall warning system must be installed. However, the manufacturer produced a marketing video prior to STC approval claiming the stall warning system was not required in the U.S. The company stated that this tape was used for training and served as a basis for pilots to routinely disable the stall warning horn by pulling the circuit breaker.
Investigation Findings
At the time of the accident, the airplane lacked the required ventral fin. The flaps were set to the takeoff position, and the audible stall warning circuit breaker was found in the pulled (disabled) position. The local FAA Flight Standards Office had conducted 14 inspections of the accident airplane in the preceding 29 months, yet none referenced the missing ventral fin.