THE STUDENT PILOT DEPARTED EARLY IN THE MORNING AND WAS NOT FOUND UNTIL THE NEXT AFTERNOON. THERE WERE NO WITNESSES TO THE ACCIDENT. THE AIRCRAFT IMPACTED THE GROUND IN A 50 DEGREE NOSE DOWN ANGLE AT A HIGH RATE OF SPEED WITH EVIDENCE OF AIRCRAFT ROTATION AROUND THE LONGITUDINAL AXIS. A TOXICOLOGICAL EXAMINATION REVEALED THE PRESENCE OF A THERAPEUTIC LEVEL, 0.2 UG/ML OF DIAZEPAM, (VALIUM) IN THE PILOT'S BLOOD. IN ADDITION 56 NG/ML OF MARIJUANA METABOLITE WERE FOUND IN THE URINE AND 27 NG/ML OF 9-CARBOXY-THC, THE PRINCIPAL METABOLITE OF TETRAHYDROCANNABINOL WHICH IS THE PRINCIPAL PSYCHOACTIVE CONSTITUENT OF MARIJUANA, WERE FOUND IN THE PILOTS BLOOD. THE DETECTED CONCENTRATION OF MARIJUANA METABOLITE IN BLOOD IS ASSOCIATED WITH MARIJUANA USE WITHIN THE PRIOR HALF DAY; AND THE COMBINATION OF VALIUM AND RECENT MARIJUANA USE MAY RESULT IN AN ADDITIVE EXTENT OF IMPAIRMENT.