On June 20, 1999, at 1215 central daylight time, a Libersat Kolb Mark 3 amateur-built experimental airplane, N106RL, owned and operated by the pilot, was substantially damaged upon impacting a tree and terrain while maneuvering near Vidor, Texas. The private pilot, sole occupant and builder of the airplane, was seriously injured. Visual meteorological conditions prevailed and a flight plan was not filed for the 14 Code of Federal Regulations Part 91 personal flight, which originated from Orange County, Texas, at 0900. According to a telephone interview conducted by the FAA inspector, who examined the accident site, the pilot reported that he circled around his property about two times after practicing landings at the Orange County airport. On the third pass at 800 feet agl, he initiated a left turn from a heading of 360 degrees to 270 degrees, and the aircraft entered a "slip." The pilot added that he could not recover from the slip and was losing altitude. The FAA inspector stated that the airplane was in a left hand turn when it clipped the top of a 75 foot tall pine tree. Subsequently, the airplane spun around and impacted the ground in a nose low attitude. In the enclosed Pilot/Operator Aircraft Accident Report (NTSB Form 6120.1/2), the pilot stated that his wife and son, who witnessed the accident, reported that the "engine was not running right;" however, he could not hear the engine, due to the helmet and built-in headset he was wearing. The pilot added in the report that "all controls were working, elev., ail., & rudder." The FAA inspector reported that the left wing's spar was fractured and bent up, the cockpit area was compromised, and the landing gear was bent up. Additional damage was sustained by one of the propeller blades. The FAA inspector stated that the engine crankshaft could be rotated by hand. He added that he found automobile gasoline and oil in the Rotax engine. One of the two carburetors was separated from the engine. No anomalies were found that would have prevented operation of the engine. At 1153, the reported weather conditions at Beaumont, Texas, which is 10 miles south of Vidor, Texas, were winds from 110 degrees at 8 knots, visibility 9 statute miles, ceilings broken at 2,700 feet agl, temperature 86 degrees Fahrenheit, dewpoint 75 degrees Fahrenheit, altimeter setting of 30.03 inches of Mercury.