What was found
DURING TAKEOFF, BOTH PROP DRIVE BELTS BROKE CAUSING LOSS OF THRUST. ACFT DESCENDED RAPIDLY AND IMPACTED THE TERRAIN. BELTS HAD CONSUMED 220 HRS OF 300-HOUR REPLACEMENT TIME. FAILURE NOT SPECIFICALLY DETERMINED, BUT COULD INCLUDE CAUSAL FACTORS SUCH AS UNEVEN WEAR OR TENSION, OR FAILURE OF ONE BELT CAUSING FAILURE OF SECOND DUE TO ENTANGLEMENT. A SINGLE WIDE BELT IS ONLY CONFIG NOW AVAILABLE FROM ENG MFG. SUBMITTER RECOMMENDED ALL 2 BELT CONFIGS STILL IN USE BE CLOSELY INSPECTED AND ADJUSTMENT VERIFIED. (X)