On June 5, 1999, about 1248 eastern daylight time, a Cessna 152, N68762, registered to Chapel Hill Flying Club, crashed during a go-around at Horace Williams Airport, Chapel Hill, North Carolina, while on a Title 14 CFR Part 91 instructional flight. Visual meteorological conditions prevailed at the time and no flight plan was filed. The aircraft was destroyed and the student pilot received serious injuries. The flight originated from Chapel Hill, the same day, about 1100. The pilot stated to an FAA inspector after the accident that he did not remember anything about the accident. A flight instructor in another aircraft stated that as he and his student entered right downwind for runway 27 at Horace Williams Airport, they observed N68762 turn from base leg to final approach, while still at about traffic pattern altitude. He diverted his attention and when he looked back, he saw N68762 about half way down the runway , still at a high altitude. A few moments later he observed N68762 over the trees at the end of the runway, in a nose-high attitude and moving very slowly, on the edge of a stall. The aircraft then yawed sharply left and disappeared into the trees in a steep nose down , near vertical attitude. Postcrash examination of the aircraft was performed by an FAA inspector. All components of the aircraft necessary for flight were on or around the main wreckage. Continuity of the flight control systems was established. The engine rotated and produced normal compression in each cylinder. Continuity of the crankshaft, camshaft, valve train and all accessory drives was established. Each magneto produced spark when rotated by hand. The carburetor was loose at the attach point to the engine and the case halve screws were loose. There was no indication of failure or malfunction of the carburetor. Postcrash toxicology testing performed on specimens obtained from the pilot during hospital admission shortly after the accident was performed by McLendon Clinical Laboratories, University of North Carolina Hospitals, Chapel Hill, North Carolina and Federal Aviation Admonistartion, Toxicology and Accident Research Laboratory, Oklahoma City, Oklahoma. The McLendon Clinical Laboratories tests were positive for Cannabinoid, Amphetamine, Opiate, and Salicylate in urine. Quantities were not established. The Federal Aviation Administration tests were positive for .019 ug/ml Tetrahydrocannabinol and .027 ug/ml Tetrahydrocannabinol Carboxylic Acid in serum. The FAA tests were also positive for .247 ug/ml Tetrahydrocannabinol Carboxylic Acid and 112.2 ug/ml Salicylate in urine. Tetrahydrocannabinol (THC) is the active substance in marijuana and tetrahydrocannabinol carboxylic acid is the inactive metabolite of THC.