PART 135 PA31 PLT IS CONCERNED WITH ATC CLRNC FOR APCH; BUT DEVIATES OFF ADF FINAL APCH COURSE AND NAV ERROR IS CAUGHT BY CTLR.

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I (X) ASKED ZOB FOR A PRACTICE NDB APCH TO RWY 23 AT ARNOLD PALMER REGIONAL ARPT (LBE). I WAS E OF THE NDB (BENJE-BHU) WHEN CTR TOLD ME TO FLY HEADING 310 DEGS. HE ALSO TOLD ME I WOULD 'HAVE TO DO THIS APCH ON MY OWN.' I ASSUMED THIS TO MEAN I WOULD BE RESPONSIBLE FOR MY OWN TFC AND TERRAIN SEPARATION. AFTER THE APCH; I REALIZED HE MAY HAVE WANTED ME TO DO THE PROC TURN. HOWEVER; WHEN BEING RADAR VECTORED; A PROC TURN IS NOT NECESSARY ACCORDING TO THE AIM. IN ADDITION; WHEN I WAS CLRED FOR THE APCH; I WAS ALREADY ESTABLISHED INBOUND ON THE 233 DEG COURSE TO THE NDB OUTSIDE OF TINEY INTXN. AT THIS LOCATION; ACCORDING TO THE APCH CHART; I WOULD HAVE BEEN ON THE PROC TURN INBOUND WITH NO NEED (OR CLRNC) TO GO AROUND THE HOLDING PATTERN. WHEN I LEARNED HOW TO FLY INSTS; I WAS TAUGHT THERE WAS 2 KINDS OF APCHS; A STRAIGHT-IN (NO PROC TURN) APCH; AND A FULL (PROC TURN) APCH. IF THE CTLR WANTED ME TO DO THE PROC TURN; HE SHOULD HAVE STATED 'CLRED FOR THE FULL NDB RWY 23 APCH.' I STILL DON'T KNOW WHAT 'YOU'LL HAVE TO DO THIS APCH ON YOUR OWN' MEANS. HOWEVER; I SHOULD HAVE ASKED. ONCE ESTABLISHED BTWN TINEY AND BHU I DSNDED FROM THE LAST ASSIGNED ALT TO 3900 FT. MY ADF SHOWED I WAS ON COURSE; BUT THE ARPT WAS OFF TO THE R. APPARENTLY THE RIDGELINE TO THE E OF THE FINAL APCH COURSE AFFECTED THE ACCURACY OF THE NDB AND LED ME OFF COURSE. THE CTR CTLR TOLD ME I WAS OFF COURSE AND BELOW HIS MINIMUM SECTOR ALT (WHICH ARE NOT PUBLISHED ON APCH CHARTS). I THEN PROCEEDED VISUALLY BACK ON COURSE TO THE ARPT. CORRECTIVE ACTIONS COULD HAVE BEEN THE USE OF 'FULL APCH' OR 'STRAIGHT-IN APCH' BY ATC; MY QUESTIONING ON UNCLR INSTRUCTION; AND BETTER FAA MONITORING OF THE ACCURACY OF NAVAIDS ESPECIALLY NDB'S.