DRG ARRIVAL TO PICK UP A MED-EVAC PATIENT, THE FLT WAS CLRD FOR AN LDA-1 RWY 8 APCH VIA THE ASORT TRANSITION. THUS, THE PLT SHOULD HAVE CONTD SE ON J-541 TWD THE SSR VORTAC & INTERCEPTED THE LOCALIZER (LOC) AT ASORT; THEN TRACK INBND ON THELOC (062 DEG), USING I-JDL FREQ 109.9 MHZ (FREQ FOR LOC & CO-LOCATED DME). AFTER ASORT, MIN ALT WAS 6500' TO DIBOL INTX,5100' TO LYNNS INTXN & 3400' TO THE FAF AT BARLO INTXN. DME FM I-JDL TO THE INTXNS WAS: 18.2, 13.5 & 8 MI. DME FM SSR (SOUTH OF LOC TRACK) TO THE INTXNS WAS 11.2, 12.7 & APRX 16 MI. FLT RPRTD ASORT INBND WHILE DSCNDG THRU APRX 9500'. LASTRDO CALL WAS 30 SEC LATER WHILE DSCNDG THRU 8200', 14 MI WEST OF DIBOL. APRX 4 MI WEST OF DIBOL, ACFT IMPACTED MTN SIDE AT 3500' MSL. NO PREIMPACT MECH MALFUNCTION WAS FND. THERE WAS EVIDENCE THAT BOTH NAV'S WERE TUNED TO 109.9 MHZ, BUT DME CTL HEAD WAS INADVERTENTLY LEFT IN 'HOLD' PSN (LOCKING DME TO SSR RATHER THAN I-JDL) & CREW BEGAN A PREMATURE DSCNT.JUNEAU WX WAS IN PART: 600' SCATTERED, 3000' OVERCAST, 7 MI VISIBILITY. PIC WAS CURRENTLY FLYING BOTH LEARJET & DHC-7.