A BE35 PLT IN CONTACT WITH FOE MAKES AN APCH TO TOP ARPT IN ERROR.

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I WAS FLYING AT THE MEA (3000 FT) PLANNING A VOR APCH TO FORBES FIELD. CLOUD BASES WERE RAGGED AT MY ALT. I SPOTTED WHAT I BELIEVED TO BE FORBES FIELD AND CANCELED MY IFR FLT PLAN. I THEN CONTACTED THE TWR AT FORBES AND RETURNED POS-INTENT. THE TWR CTLR DID NOT HAVE VISUAL CONTACT AND TOLD ME TO RPT A 2 MI FINAL. WHEN I DID; I ESTIMATED 2 MI OUT 'OVER THE RIVER.' THIS WAS THEIR CLUE THAT I WAS AT THE WRONG FIELD. THEY TOLD ME I WAS PROBABLY AT BILLARD FIELD AND GAVE ME THE TWR FREQ THERE. I IMMEDIATELY TURNED AWAY AND CONTACTED THE BILLARD TWR; GOT LNDG CLRNC; AND LANDED. OF COURSE; I COULD HAVE BEEN BETTER PREPARED; BUT I THINK THE CTLRS COULD BE MADE AWARE OF THE POTENTIAL FOR A MIX-UP. BOTH FIELDS HAVE RWYS WHICH ARE APPROX ALIGNED (RWY 13 VERSUS RWY 12) WHICH FURTHER LULLED ME INTO BELIEVING I WAS AT THE RIGHT FIELD. WHEN I RPTED THE FIELD IN SIGHT; THE CTLR COULD HAVE CHALLENGED ME; OR AT LEAST ASKED IF I MIGHT BE LOOKING AT THE WRONG ARPT (BILLARD) SINCE I WAS TOO FAR AWAY FROM FORBES TO SEE IT.