On October 30, 1996, about 1800 eastern standard time, a Let L-13 "Blanik" glider, N15CB, collided with trees during the final approach to the Chilhowee Glider Port, Benton, Tennessee. The glider was operated under the provisions of Title 14 CFR Part 91, and visual flight rules. A flight plan was not filed for the local instructional flight. There were serious injuries to the private pilot under instruction, minor injuries to the airline transport instructor, and substantial damage to the glider. Origination of the flight was Benton, Tennessee, about 1730 on the same day. The instructor stated that when the glider was turned onto the final approach for landing on runway 21, the sun was directly in their eyes. He stated that the glare on the canopy was causing very poor visibility. He was able to barely see the runway directly in front of the aircraft and side visibility was nil. The pilot under instruction continued the final approach descent and collided with a tree short of the runway. Both pilots stated they did not see the tree until the collision occurred. The instructor indicated in his report of the accident that the tree was about 300 feet from the end of the runway. Airport information obtained from an Internet file entitled "Airnav" regarding the airport indicated that the runway 21 threshold is displaced 200 feet. A 36 foot tree is listed as an obstacle, located 500 feet from the threshold and 110 feet right of the centerline. The slope to clear the tree is listed as 13:1.