AT ABT 2158 MDT, THE EMERG MED SVC (EMS/MEDEVAC) HELICOPTER (HEL) PLT CTCD BILLINGS TWR & ADZD HE WOULD BE MAKING APCHS TO SAINT VINCENTS HOSP FOR (NGT) CURRENCY. APRX 9 MIN LATER, HE CTCD THE TWR AGAIN & ADZD HE WAS BEING DISPATCHED ON AN EMS FLT. THE EMS FLT WAS TO A RANCH (WNW OF BILLINGS). THE PLT HAD DIFFICULTY FINDING THE RANCH AT NGT, BUT ARRIVED AT 2238 MDT. THE PATIENT WAS LOADED & THE PLT WAS ADZD OF TRRN CONDS. A WITNESS SAID THE HEL LIFTED OFF FAST, THEN SWIVELEDARND QUICKLY (TOWARD EAST) & TOOK OFF W/O HESITATION. AFTER DEPG, THE HEL CROSSED A HILL & CRASHED AT HI SPD ON LWR TRRNIN A SLGT NOSE LOW, RGT BANK ATTITUDE, HDG 330 DEG. NO PREIMPACT MECH PRBLM WAS FND. THE PLT HAD BEEN RECENTLY HIRED BY THE OPERATOR; PREV EMPLOYMENT INVOLVED FLYING A DISSIMILAR HEL (BK-105) IN THE GULF OF MEXICO AREA, LIMITED TO DAY VFR. THE PLT'S LAST RECORDED NGT FLT WAS ON 6/16/87; HIS LAST RECORDED INST FLT WAS PRIOR TO JUNE 1984. NO RECORD WAS FND OF FAMILIARIZATION TRAINING FOR THE GEOGRAPHICAL AREA. RELATIVES OF THE PATIENT DESCRIBED THE ACDNT AREA AS A BLACK HOLE.