What happened
On July 27, 2017, an Aerofab Inc Lake LA 4 250 amphibious airplane, registration N1400P, crashed into the water at Vette/Blust Seaplane Base in Oshkosh, Wisconsin. The accident resulted in 2 fatal injuries and 1 minor injury.
Earlier that day, the pilot had addressed issues with the left wing sponson, which had been taking on water. After draining the water and fuel from the sponson and performing a field repair on a missing inspection cover, the pilot prepared for departure. Despite warnings from the harbormist and other pilots regarding deteriorating water conditions—specifically waves measuring 1.5 to 2 feet, which exceeded the aircraft's maximum demonstrated wave height of 18 inches—the pilot elected to depart.
The pilot chose to perform a takeoff in a northwesterly direction, which resulted in a downwind takeoff into large waves. As the aircraft was being towed out of the harbor, the pilot repeatedly attempted to start the engine before the tow line was cleared. Once the tow was complete, the pilot applied full power. The aircraft accelerated for approximately 60 seconds before porpoising and the nose rising steeply. The airplane then rolled to the left, the left wing struck the water, and the aircraft spun and sank.
Findings
Investigation of the wreckage and flight sequence revealed that the wing flaps were in the retracted position during the takeoff, despite the airplane's flight manual and a visible checklist on the instrument panel stating that flaps should be down for all takeoffs and landings. While a passenger recalled the pilot verbalizing that the flaps were down, physical evidence and video footage confirmed they were retracted.
Mechanical examination of N1400P showed that the engine was performing normally and all control surfaces remained continuous with the cockpit controls. The elevator trim was found near the neutral position.