AT 0716, THE PILOT RCVD A WX BRIEF FOR A PROPOSED TAKEOFF OF 1130. THE FSS BRIEFER PROVIDED INFO ON TSTMS FORECAST IN GA & FL. NO INFO WAS PROVIDED ABOUT FORECAST LINES & CLUSTERS OF TSTMS IN SC CSTL PLAINS & SERN GA. EN ROUTE, THE PILOT WAS GIVEN INFO ABOUT LEVEL III TSTMS ACROSS THE PROJECTED FLIGHT PATH BY BEAUFORT & SAVANNAH APPCH CNTRL. ATC RADAR DATA REVEALED THAT THE ACFT FLEW THE ROUTE CONTAINED IN THE FLIGHT PLAN CLEARANCE. RADIO TRANSMISSIONS FROM THE ACFT INDICATED THAT ONBOARD WX RADAR WAS BEING USED. ATC RADAR DATA & RADIO COMMUNICATIONS INDICATED THAT THE ACFT ENTERED A TSTM, THEN MADE A 180 DEGREE TURN TO EXIT THE STORM. EXAMINATION OF THE WRECKAGE REVEALED PLASTIC DEFORMATION OF THE WINGS INBOARD OF THE ENGINES IN AN UPWARD DIRECTION. ALSO, BOTH WINGS BROKE OFF OUTBOARD OF THE ENGINES IN A DOWNWARD DIRECTION. THE HORIZONTAL STAB & ELEVATOR WERE NOT RECOVERED. THERE WAS FUSELAGE DAMAGE WHICH INDICATED THAT THE HORIZONTAL STAB SEPARATED AFT & DOWN.