BASED ON AVAILABLE EVIDENCE, IT IS BELIEVED THAT THE ACCIDENT OCCURRED BETWEEN 0700 AND 0830 HRS DURING A PERIOD OF LOW CEILINGS AND RESTRICTED VISIBILITIES IN THE AREA WHERE THE ACCD TOOK PLACE. THE ACCD SITE IS LOCATED IN A MOUNTAIN PASS AREA BETWEEN TWO VALLEYS. THE DEPT POINT, TIME, ROUTE OF FLT, AND DEST OF THE FLT ARE UNK. A WHITE POWDERY SUBSTANCE, LATER IDENTIFIED AS METHAMPHETIMINE, WAS FOUND WIDELY DISTRIBUTED THROUGHOUT THE CABIN AREA AND THE SORROUNDING GROUND AT THE ACCD SITE. EXAM OF THE WRECKAGE INDICATED THAT THE ACFT COLLIDED WITH THE 46 DEGREE SLOPE OF THE MOUNTAIN IN A HIGH SPEED DESCENT AT AN ANGLE OF ABT 45 DEGREES NOSE DOWN. NO PREIMPACT MECHANICAL MALFUNCTIONS OR FAILURES WERE IDENTIFIED DURING THE INVESTIGATION. THE ACFT HAD NOT HAD AN ANNUAL INSPECTION IN TWO YEARS AND THE LAST DOCUMENTED BFR FOR THE PLT WAS IN AUGUST OF 1983. THE RESULTS OF THE TOXICOLOGICAL TESTS WERE NEGATIVE FOR ALCOHOL AND ALL DRUG SUBSTANCES.