On September 10, 1994, at 1315 eastern daylight time, a ASW-15 (Glider), N827, registered to and piloted by William L. Christie, sustained substantial damage at Dansville Airport, Dansville, New York. The pilot was not injured. Visual meteorological conditions prevailed, and no flight plan was filed. The flight was operated under 14 CFR Part 91. According to the pilot's statement on the NTSB Form 6120.1/2, he elected to extend the downwind leg due to powered aircraft traffic ahead of him on the approach. When the pilot turn from base to final he saw another powered airplane ahead and lower. The powered airplane saw the glider and discontinued his approach. The glider pilot wrote: ...next I looked at approach and decided not to employ spoilers as the distance was too far. Within seconds my altitude an speed was reduced, I reacted by pushing forward on [the] control stick to gain speed. The sailplane did not respond...I was being forced down from above at a rapid rate...I thought [this] was a violent down draft.... The glider struck a tree with the left wing about 400 feet short of runway 30.