AT 0833 ADT, THE ACFT DEPARTED BETHEL, AK ON A SCHEDULED PAX/CARGO COMMUTER FLT TO CHEVAK, SCAMMON BAY & HOOPER BAY, AK. THE OPERATOR'S COMMUTER FLTS HAD NOT LANDED AT SCAMMON BAY FOR SVRL DAYS SINCE THE RWY WAS SOFT & MUDDY FROM MELTINGSNOW. BFR DEPARTING CHEVAK, 902 LBS OF MAIL & BAGGAGE WAS PLACED IN THE AFT BAGGAGE COMPARTMENT. ALSO, 2 PAX'S WERE ASKED TO SIT IN THE MOST AFT SEATS "TO LIGHTEN THE NOSE." AT SCAMMON BAY, THE UNEVENTFUL LNDG WAS MADE FROM A SHALLOW APCH WITH HI PWR. AFTER LANDING, 278 LBS OF MAIL WAS REMOVED FROM THE NOSE COMPARTMENT, LEAVING IT EMPTY, & 191 LBS OF CARGO WAS REMOVED FROM THE CABIN. THIS WAS DONE WITH 1 ENG RUNNING, NO OTR LOAD CHGS WERE MADE BFR TKOF. THE PAX RPRTD THAT DRG APCH TO HOOPER BAY, THE PWR WAS REDUCED ON A SOMEWHAT STEEPER APCH & THE SQUARE (FLAP) HNDL WAS MVD. THEY RPRTDTHAT SOON THEREAFTER, THE NOSE PITCHED UP & STALL WRNG SOUNDED. THE PLANE CRASHED APRX 1320 FT SHORT OF RWY 13. AN INVESTIGATION REVEALED THE CG WAS APRX 7.7% BHND THE MAX AFT LMT. NO PREIMPACT, MECHANICAL FAILURE WAS FOUND.