THE PILOT HAD NOTIFIED JACKSON AUTOMATED FLIGHT SERVICE STATION OF HIS INTENTION TO FLY FROM JACKSON, TN, TO TULLAHOMA, TN, AT 3000' MSL. ALONG THE ROUTE NEAR MOUNT PLEASANT, WITNESSES HEARD A LOUD BANG. SHORTLY AFTERWARDS, WRECKAGE FROM THE HELICOPTER WAS FOUND SCATTERED OVER A 1500' PASTURE AREA. EXAMINATION OF THE WRECKAGE REVEALED THAT A MAIN ROTOR BLADE HAD DIVERGED FROM ITS NORMAL PLANE OF ROTATION & STRUCK THE LEFT DOOR FRAME IN-FLIGHT. VISUAL METEOROLOGICAL CONDITIONS PREVAILED. ABOUT 35 MILES NORTH-NORTHEAST AT NASHVILLE, THE 1647 CDT SURFACE WIND WAS REPORTED TO BE FROM 010 DEGREES AT 10 GUSTING 21 KNOTS; WINDS ALOFT AT 3000' WERE REPORTED AS 22 KNOTS. DARK CLOUDS WERE REPORTED NORTHWEST OF THE ACCIDENT SITE. THERE WAS NO EVIDENCE OF MECHANICAL MALFUNCTION PRIOR TO THE IN-FLIGHT STRIKE OF THE AIRFRAME.