On June 23, 2010, about 1425 eastern daylight time, an experimental, amateur-built SeaWind 3000 amphibian airplane, N79DJ, operated by an airline transport pilot (ATP), was substantially damaged during descent near Sanibel Island, Florida. The certificated ATP and passenger were not injured. The personal flight was conducted under the provisions of 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed and no flight plan was filed for the planned flight to Sarasota/Bradenton International Airport (SRQ), Sarasota, Florida. The flight originated from Key West International Airport (EYW), Key West, Florida, about 1345. The pilot reported that the airplane was descending through 6,000 feet mean sea level, over the Gulf of Mexico, about 40 miles west of Southwest Florida International Airport (RSW), Fort Myers, Florida, when a vibration developed in the elevator control. The pilot reduced engine power, and the vibration decreased. When the pilot increased engine power, the vibration increased and he had to reduce engine power to a point where the airplane could not maintain altitude. The pilot subsequently performed a forced landing to water, about 200 feet offshore of Sanibel Island. The landing was hard, which resulted in damage to the engine nacelle and empennage. Postaccident examination of the airplane by a Federal Aviation Administration inspector revealed that a portion of the elevator had separated in-flight. The pilot attributed an initial vibration as a result of a separated elevator balance horn. The vibration steadily increased, and the pilot believed the increased vibration ultimately caused the separation of the second elevator balance horn. Subsequently, three-fourths of the elevator separated and the airplane began to shake. The separated elevator and balance horns were not recovered. Approximately one-fourth of the elevator remained attached to the airplane and was forwarded to the NTSB Materials Laboratory, Washington, DC, for further examination. Metallurgical examination of the elevator revealed that the adhesive exposed in the areas where the skin was missing had remnants of carbon fibers still bonded in it, which was consistent with an overload failure and not an adhesive failure. The bottom surface of the elevator trim tab was missing the entire skin panel. The missing skin on the bottom surface of the elevator was consistent with the elevator failing in the downward direction and the skin peeling off the bottom surface as the outboard portions of the elevator departed. The four-seat, high-wing, amphibian airplane, serial number 48, was equipped with a Lycoming IO-540-EXP, 400-horsepower engine. The pilot, who was also the owner/builder, completed construction of the airplane on June 4, 2010. The airplane had accrued 43 total hours of operation since its completion. The airplane was equipped with an empennage manufactured by Precision Design. The pilot reported that Precision Design offered an empennage with increased performance at less cost than an empennage manufactured by SeaWind. According to the owner of Precision Design, the company had not manufactured any parts for SeaWinds in about 10 years prior to the accident. He estimated that Precision Design made about 20 SeaWind empennage sections in total. According to the owner of SeaWind, Precision Design stopped producing SeaWind empennage sections about 2002. The owner added that Precision Design offered an empennage that was 49 percent larger than the SeaWind empennage. Although the increased size did not add much weight, it added significant surface area, resulting in increased gust loads, with no added engineering to compensate for such loads. The owner believed that there were approximately 10 Precision Design empennage sections on the market, and he was aware of three (including the accident airplane) that went in to flutter. The owner further stated that he was concerned some owner/builders were not heeding the recommendations of the experimental SeaWind 3000 kit. He noted that the maximum rated engine recommended for the airplane was 300 horsepower; however, the accident airplane had a 400-horsepower engine, and some owner/builders are installing turbine engines. The owner stated that the airplane's never exceed speed (Vne) was 230 mph (200 knots) and the maneuvering speed (Va) was 180 mph (156 knots). Review of a radar plot for the accident flight, overlaid on top of weather radar data, revealed that the accident airplane was traveling at a groundspeed of approximately 200 knots, in the vicinity of convective activity. Southwest Florida International Airport (RSW), Fort Myers, Florida, was located about 20 miles east of Sanibel Island. The reported weather at RSW, at 1453, was: wind from 060 degrees at 14 knots, gusting to 19 knots; visibility 10 miles; few clouds at 5,000 feet; temperature 35 degrees Celsius (C); dew point 22 degrees C; altimeter 30.05 inches of mercury.