On July 16, 2017, about 2010 eastern daylight time, an experimental light sport Aeroprakt A-20 Vista Cruiser, N55US, was substantially damaged during a forced landing into trees, following a total loss of engine power on final approach to Brookhaven Airport (HWV), Shirley, New York. The private pilot was 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 local flight.The pilot reported that he was performing touch-and-go landings to runway 24 at HWV. About 700 feet above ground level, the airplane encountered a downdraft and the engine lost all power. The pilot was unable to restart the engine and realized that the airplane would not glide all the way to the runway. He elected to land in the tops of trees approximately .3 mile from the runway threshold. The airplane subsequently contacted the tree tops and descended left wing low to the ground. Examination of the wreckage by a Federal Aviation Administration (FAA) inspector revealed substantial damage to the wings and fuselage. The airplane was equipped with a Rotax 912 S, 100-horsepower engine. Subsequent examination and successful test-runs of the engine by the pilot and FAA inspectors did not reveal any preimpact mechanical malfunctions. The engine operated continuously at multiple power settings, including full power. The engine's choke control was located in the vicinity of the throttle lever. During one of the test-runs, the pilot and FAA inspectors noted that when the choke control was moved approximately halfway (1 inch), the engine lost all power. The pilot and inspectors believed that during the downdraft/turbulence encounter, the pilot's hand on the throttle accidentally bumped the choke control, which resulted in a total loss of engine power.