C172 ON IFR ARRIVAL TO UNCONTROLLED ARPT ENCOUNTERS OTHER INBOUND TRAFFIC. FAILURE OF POSITION REPORTS TO BE TRANSMITTED ON CTAF CONTRIBUTED.

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I WAS INBOUND TO MWL ON AN ACTIVE IFR FLT PLAN. WX CONDITIONS 10 MINS PRIOR TO ARR (APPROX XA45) WERE RPTED (MWL ASOS) TO BE CEILING BROKEN AT 600 FT WITH 5 SM VISIBILITY. I WAS GIVEN VECTORS TO THE FINAL APCH COURSE; AND THEN CLRED FOR THE ILS RWY 31 APCH INTO MWL BY ZFW. WX CONDITIONS 5 MINS PRIOR TO ARR WERE RPTED AS CEILINGS BROKEN AT 100; BROKEN AT 500 WITH VISIBILITY 1 SM IN FOG. NOTE THAT ACTUAL OBSERVED CONDITIONS AT LNDG WERE ESTIMATED TO BE 2 SM VISIBILITY AND CEILING BROKEN AT 500 FT. NO CLOUD LAYER AT 100 FT AGL WAS OBSERVED. PRIOR TO FAF CURTIS; ZFW APPROVED FREQ CHANGE TO ADVISORY. I CHANGED TO MWL CTAF AND RPTED 4 MI FINAL AND 2 MI FINAL. ABOUT 2 MI FROM THE THRESHOLD; I GLIMPSED 'SOMETHING' THROUGH THE BROKEN LAYER THAT APPEARED TO BE ON THE FAR SIDE OF THE ARPT. ABOUT 1 MI FROM THE THRESHOLD; AT APPROX 300 FT AGL UNDER A 500 FT AGL CEILING; I OBSERVED ANOTHER ACFT ON THE EQUIVALENT OF A R DOWNWIND LEG TO RWY 31. OTHER ACFT WAS AT A RANGE OF APPROX 1500 FT AT APPROX 2 O'CLOCK POS AND APPROX 100 FT ABOVE (APPROX 100 FT BELOW THE CLOUD LAYER). I CONTINUED APCH TO LNDG; TAXIED CLR OF THE RWY; THEN CANCELED IFR CLRNC WITH ZFW VIA RELAY THROUGH ANOTHER ACFT. ONCE PARKED THE UNICOM OPERATOR EXPLAINED THAT HE WAS AWARE OF THE CONFLICT (AND TRIED TO ASSIST ON THE RADIO) BECAUSE HE COULD SEE ME ON COMPUTER PROGRAM AND COULD HEAR THE OTHER ACFT ON CTAF. THE UNICOM OPERATOR RPTED NEVER HEARING MY CALLS ON CTAF. MYSELF AND UNICOM OPERATOR COMPARED FREQS (122.72); BUT WERE UNABLE TO VERIFY RADIO TUNING SINCE THE RADIO HAD BEEN CHANGED TO CANCEL IFR CLRNC AFTER LNDG. THE RADIO WAS SUBSEQUENTLY TUNED AND CHKED AT MWL SUCCESSFULLY. THE ASSUMPTION IS THAT THERE WAS A RADIO PROB; OR TUNING ERROR THAT RESULTED IN THE 2 CTAF CALLS ON FINAL APCH NOT BEING HEARD. THE OTHER ACFT LANDED BEHIND ME AND TAXIED TO PARKING. SEVERAL MINS LATER; THE PLT OF THE OTHER ACFT CAME OVER TO DISCUSS THE SITUATION. HE WAS NOTICEABLY UPSET ABOUT NOT HEARING CTAF RADIO CALLS FROM ME; AS HE 'HAD HIS WIFE IN THE PLANE AND THAT JUST WASN'T SAFE.' I RPTED MAKING THE CTAF CALLS ON FINAL; BUT SAID THERE WAS A POSSIBILITY OF A RADIO TUNING MISTAKE. I INQUIRED IF THE OTHER PLT WAS FLYING UNDER AN IFR CLRNC; SINCE MWL HAS A CLASS E SURFACE AREA AND WAS RPTING WX BELOW VFR MINIMUMS. THE OTHER PLT RPTED THAT HE DID HAVE A CLRNC AND WAS 'THINKING OF DOING SOME APCHS.' I ASKED THE OTHER PLT TO CONFIRM THAT HE WAS OPERATING UNDER AN ACTIVE IFR CLRNC; SINCE THAT WOULD INDICATE THAT ATC HAD CLRED 2 ACFT INTO THE SAME SPACE AT THE SAME TIME. THE OTHER PLT BECAME UPSET AND DISCONTINUED THE CONVERSATION.