What happened
While flying approximately 2.5 miles south of the airport, the pilot of a two-place glider began encountering downdrafts. The pilot initially attempted to fly back toward the airport at a speed of 63 mph.
As the aircraft reached an altitude of approximately 2,000 feet agl, located about 1.5 miles south of the airport, the pilot observed a descent rate indication of approximately 600 fpm. Believing that the airport could not be reached, the pilot elected to attempt an off-airport landing.
The investigation
An analysis of the aircraft's performance indicated that the manufacturer's published best glide speed for the two-place glider was 50 mph. At this speed, the lift-to-drag ratio was 23-1, which would have allowed for a glide of approximately 8 miles from an altitude of 2,000 feet. A review of weather reports determined that the aircraft would have been experiencing a left quartering tailwind while flying from south to north.