On November 21, 1999, at 1603 eastern standard time, a homebuilt Kitfox, N993DB, was substantially damaged when it impacted terrain near Westminster, Maryland. The certificated student pilot and passenger sustained serious injuries. Visual meteorological conditions prevailed for the personal flight that originated from a grass strip near Liberty Town, Maryland. A flight plan was not filed for the flight conducted under 14 CFR Part 91. According to the pilot, he arrived at the private airstrip with his wife, about 1200. He made some repairs to the airplane's intercom system, then conducted a preflight. During the preflight he checked that the fuel quantity was full, and he noticed no anomalies with the airplane. Both he and his wife boarded the airplane, and the engine started on the first attempt. He completed the run-up check in front of the hangar, then taxied to the south runway. Once on the grass strip, the pilot advanced the throttle and departed. He flew approximately 15 minutes to visit a friend, landed, and shut down the airplane's engine. After approximately 45 minutes, the pilot and his wife re-boarded the airplane, and departed via the northeast runway for a second destination. The pilot climbed to a cruise altitude of 1,000 feet msl, and flew approximately 30 minutes. Then, while maneuvering the airplane onto a 45 degree downwind entry at 200 feet agl, the pilot saw an ultra light on a converging heading. He banked the airplane to the right, advanced the throttle, and initiated a climb. Once clear, the pilot began a turn to the left to follow the ultra light onto the downwind, but while turning, the airplane entered an "accelerated stall." The pilot estimates that at the time of the stall the airplane was nose up approximately 10 degrees, and banking to the left approximately 15 degrees.