THE AIRCRAFT WAS OPERATING AS CONTINENTAL EXPRESS FLIGHT 2286. DURING THE APPROACH IN IFR CONDITIONS, THE AIRCRAFT WENT BELOW THE MINIMUM DESCENT ALTITUDE THEN STRUCK THE TERRAIN AT 7180 FEET MSL. EXAM OF THE AIRCRAFT DID NOT DISCLOSE ANY PRE-IMPACT FAILURES OR SYSTEM MALFUNCTIONS. THE EVIDENCE INDICATED THAT THE COPILOT WAS FLYING THE AIRPLANE DURING THE APPROACH. EVALUATION OF THE RADAR DATA SHOWED AN EXCESSIVE RATE OF DESCENT BEFORE THE COLLISION WITH TERRAIN. POST- MORTEM TOXICOLOGICAL EXAMINATION SHOWED THAT THE CAPTAIN HAD USED COCAINE PRIOR TO THIS FLIGHT. THE SAFTEY BOARD CONCLUDED THAT THIS USE HAD ADVERSLY AFFECTED HIS ABILITY TO MONITOR THE UNSTABILIZED APPROACH FLOWN BY THE COPILOT. RECORDS OF BOTH CREWMEMBERS REVEALED PRIOR TRAFFIC VIOLATIONS AND ACCIDENTS, AND, IN THE CASE OF THE CAPTAIN, A PREVIOUS AIRCRAFT ACCIDENT. EVALUATION OF THE WEATHER CONDITIONS INDICATED THAT A 10 TO 15 KNOT TAILWIND CONDITION EXISTED THROUGHOUT THE APPROACH.