What happened
A float-equipped airplane was observed taking off in light winds and calm water. During the initial climb, the aircraft achieved a nose-high attitude and a steep climb angle. Witnesses noted that there was no audible reduction in engine noise, suggesting the engine remained at takeoff power rather than transitioning to climb power. Approximately 200 feet above the water, the airplane entered a steep left bank before rolling rapidly to the right and impacting the water at a steep angle.
The investigation
The aircraft had been modified with a Short Take Off and Landing (STOL) kit. Certification flight tests for this modification revealed that the kit eliminated the aerodynamic warnings typically associated with an impending stall, making an audible stall warning system mandatory. Furthermore, test results indicated that to meet directional stability certification requirements, both a ventral fin and horizontal stabilizer finlets were required. These tests specifically identified the takeoff flap configuration during climb as the least stable flight condition.
The Supplemental Type Certificate (STC) for the STOL modification mandated the installation of the ventral fin and the audible stall warning system. Investigators found that at the time of the accident, the ventral fin was not installed on the aircraft. Additionally, the takeoff flaps setting was selected, and the circuit breaker for the audible stall warning horn had been pulled, effectively disabling the system.
Investigators also noted that a marketing video produced by the manufacturer prior to STC approval stated the stall warning system was not required in the United States. The company stated this video was used for training, which contributed to a practice where pilots routinely disabled the stall warning horn by pulling the circuit breaker. Records showed the local FAA Flight Standards Office had inspected the aircraft 14 times over the preceding 29 months without noting the absence of the ventral fin.