SINGLE PLT SMT DESCENDS PRIOR TO CROSSING BRIEL OUTBOUND FOR ILS 23 IAP TO SLK.

Narrative

TCU/CUMULO NIMBUS CLOUDS WERE ON MOST OF THE RTE. I WAS ROUTED AROUND SOME OF IT; THEN RNAV DIRECT TO SLK. AT 15 MI OUT; THERE WAS ANOTHER BUILDUP; HVY ENOUGH I DIDN'T DEEM IT SAFE TO GO THROUGH TO GET TO THE SLK VOR; SO I ASKED FOR DIRECT BRIEL. I WAS GIVEN THAT AND TO MAINTAIN 6800 FT UNTIL BRIEL OUTBOUND AND CLRED FOR THE ILS 23 APCH. I DID NOT REPROGRAM THE RNAV; I WAS USING THE NDB ONLY FOR NAV. I WAS IN IMC AT THIS POINT; WITH MODERATE TURB. FROM PREVIOUS CONVERSATIONS WITH THE CTR CTLR AND FROM ONBOARD RADAR; I KNEW THERE WERE MORE BUILDUPS N AND S OF MY CURRENT POS BY ABOUT 25 MI IN EITHER DIRECTION. AS A RESULT; AS SOON AS I SAW THE ADF NEEDLE TURNING RAPIDLY; WHAT I BELIEVED TO BE STATION PASSAGE; AND STARTED THE DSCNT. AT 6000 FT I GOT A CALL FROM THE CTR CTLR SAYING THAT I WAS NOT OUTBOUND FROM BRIEL AND THAT I WAS 800 FT LOW. I STOPPED THE DSCNT; AND AS I HAD BROKEN OUT AND WAS IN THE VALLEY; COULD CLRLY SEE THE FIELD; I CANCELED THE IFR; DSNDED NORMALLY AND MADE AN UNEVENTFUL LNDG. THINGS I SHOULD HAVE DONE DIFFERENTLY: 1) USED THE VOR/DME AS A BACKUP FOR THE INFO RECEIVED FROM THE ADF. I BELIEVE THE ADF WAS INACCURATE DUE TO THE MOUNTAINS. 2) MORE SERIOUSLY CONSIDERED A HOLD OR DIVERSION UNTIL THE BUILDUPS HAD PASSED SO I DIDN'T HAVE TO BE SO CONCERNED WITH A DSCNT BTWN 2 BUILDUPS. I DECIDED NEITHER OF THESE OPTIONS WERE GOOD ONES CONSIDERING THE SPD AT WHICH THE BUILDUPS WERE OCCURRING; LATENESS OF THE FLT (45 MINS BEHIND SCHEDULE); AND FLT TIME (ALREADY AT 6.6 HRS AT THE TIME OF THE DECISION). I SUSPECTED I DIDN'T HAVE THE FLT TIME AVAILABLE TO DIVERT TO PLATTSBURG; WAIT OUT THE BUILDUPS; AND STILL GET INTO SARANAC LAKE. OTHER CONTRIBUTING FACTORS: FATIGUE -- THIS SHIFT IS A NORMALLY-SCHEDULED 13.5 HR DUTY DAY THAT REGULAR GOES TO 14; AND IN THAT SHIFT I FLY BTWN 6-8 FLT HRS SINGLE PLT. I BELIEVE THIS IS TOO LONG A DAY WITH TOO MUCH FLYING TIME UNDER DIFFICULT CONDITIONS.