DURING A NIGHT ARRIVAL, THE PLT WAS CLEARED FOR A VOR/CIRCLING APCH TO THE SIDNEY MUNI ARPT. THE PUBLISHED APCH WAS FROM THE HANCOCK VOR WITH A NORTHERLY HEADING TO THE ARPT OF 354 DEG. SUBSEQUENTLY, THE ACFT CRASHED & BURNED ON WOODED TERRAIN ABOUT 1 MI NORTH OF THE ARPT IN THE VICINITY OF A LEFT DOWNWIND LEG FOR RWY 7. INITIAL IMPACT OCCURRED WITH TREES AT AN ELEVATION OF ABOUT 1550 FT WHILE PARALLELING RWY 7/25 (HEADING 255 DEG). THE ELEVATION OF THE ARPT WAS 1027 FT. THE MIN DESCENT ALT (MDA) FOR THE VOR APCH WAS 2280 FT. AN EXAM OF THE WRECKAGE REVEALED NO EVIDENCE OF A PREIMPACT PART FAILURE OR MALFUNCTION. THE PROP BLADES HAD EVIDENCE OF ROTATIONAL DAMAGE. A TEST OF THE PLT'S BLOOD SHOWED AN ALCOHOL LEVEL OF 101 MGS% (.101%); HOWEVER, THE PLT'S BODY (& THE WRECKAGE) WERE NOT FOUND UNTIL 8/15/84. THERE WAS EVIDENCE THAT ALCOHOL IN THE PLT'S BLOOD WOULD HAVE RESULTED FROM PUTREFACTION. ABOUT 26 MI SW AT BINGHAMTON, NY, THE 0051 EDT WX WAS, IN PART: 1500 FT SCATTERED, 5500 FT OVERCAST, VISIBILITY 7MI, WIND 120 DEG AT 5 KTS.