WHILE EN ROUTE AT FL 370, THE PLTS DECLARED AN EMERG, RPRTD A FIRE IN THE RGT ENG & REQD VECTORS TO THE NEAREST SUITABLEARPT. THEY WERE VECTORED TWD THE LEXINGTON BLUEGRASS ARPT & CLRD TO DSCND. SHORTLY AFTER DECLARING AN EMERG, THE PLTS RPRTD THEY SECURED THE RGT ENG & EXTINGUISHED THE FIRE LGT. AS THE ACFT WAS ON FINAL APCH TO LND, THE LOCAL CTLR (USING BINOCULARS) CONFIRMED THAT BOTH THE GEAR & FLAPS WERE EXTENDED. HOWEVER, AS THE ACFT CONTD ONTO A SHORT FINAL APCH, AN INCREASE IN ITS PITCH ATTITUDE WAS NOTED. IT THEN DROPPED BELOW THE LVL OF THE RWY THRESHOLD & IMPACTED IN A PASTURE SHORT OF THE RWY. AFTER INITIAL IMPACT, THE ACFT WENT THRU A STONE FENCE, HIT 2 UTILITY POLES, CROSSED A HIWAY, CAME TO REST AT THE PERIMETER FENCE & BURNED. AN AUTO WAS DMGD BY DEBRIS; 2 OCCUPANTS RECD MINOR INJURIES. AN INV REVEALED THE ACFT IMPACTED WITH THE GEAR EXTD, BUT THE FLAPS & FLAP HANDLE WERE FND IN THE UP PSN. AN EXAM OF THE RGT ENG REVEALED ITS OUTER EXHAUST CONE WAS CRACKED IN THE VCNTY OF A FIRE DETECTION LOOP. NO OTR PREEXISTING MECH PROBLEMS WERE EVIDENT.