EE WAS OPERATING A TRACTOR BACKHOE W/HAMMER TO BREAK FROST IN GRAVEL PIT SO EXCAVATOR COULD LOAD GRAVEL. HE DROVE BACKHOE WITHIN 20 FT OF BANK IN PIT. HE STOPPED BACKHOE AND TURNED IN HIS SEAT TO OPERATE THE CONTROLS FOR THE HAMMER. THE BACKHOE STARTED TO MOVE TOWARD THE EDGE OF THE DROPOFF. BY THE TIME HE GOT TURNED AROUND TO TRY TO STOP, THE BACK HOE WENT OVER THE EDGE AND THE EE