On February 21, 1998, at 1500 eastern standard time, a PDPS PZL-BIELSKO SZD-48-3, N25MZ, collided with the trees during approach to landing in Pikeville, Tennessee. The personal flight was operated by the pilot under the provisions of Title 14 CFR Part 91 with no flight plan filed. Visual meteorological conditions prevailed at the time of the accident. The glider sustained substantial damage, and the commercial pilot received minor injuries. The flight originated in Whitwell, Tennessee at 1330. According to the FAA inspector, the glider lost thermal lift while soaring which led the pilot to attempt an emergency off-airport landing. During the descent, the glider collided with a tree. According to the pilot, he took an aerotow to the eastern edge of the valley and released at 3,500 feet above ground level (AGL). The pilot then flew approximately 22 miles to Crossville Airport, which he crossed at 3,000-3,500 feet AGL. The pilot stated he then proceeded to the western plateau where the thermal activity became about 2-4 knots of lift and 4-6 knots of sink. According to the pilot, the lifts were ill defined, and he flew mostly into sinks. As his altitude decreased to 2,500 feet AGL, he turned back to Pikeville. The glider continued to experience 4-6 knots of sink, so the pilot stated he began looking for a suitable field for landing. He overflew the landing field at 2,000 feet AGL and determined there was a fairly constant 6 knot sink. He stated he did not lower the landing gear or extend the spoilers in order to reduce drag. As he approached the field, he stated the sink increased, and he collided with trees at the approach end of his desired landing field.