A STUDENT PLT WITH A FLT INSTRUCTOR CAME WITHIN 100 FT OF AN ACFT AT AN UNCTLED FIELD.

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I WAS ON DOWNWIND ABEAM THE LNDG NUMBERS TO RWY 18 AT WITH CFI ON BOARD. I ANNOUNCED EACH LEG OF THE PATTERN. THERE WERE 2 OTHER ACFT IN THE PATTERN. WITH NO WARNING OR COMS THE AA5 SUDDENLY APPEARED AT 1 O'CLOCK POS; OPPOSITE DIRECTION; ABOUT 20 DEGS L BANK IN A L TURN. I POINTED THE ACFT OUT TO MY INSTRUCTOR WHO CALLED ON THE RADIO TO ASK THE OTHER PLT IF HE HAD HEARD US OR THE OTHER TFC ON CTAF. THE AA5 PLT RESPONDED THAT HE HEARD NOBODY. I CONTINUED THE APCH TO A TOUCH-AND-GO. THE AA5 LANDED AFTER US AND TAXIED INTO A HANGAR; THEREFORE; I DIDN'T GET HIS REGISTRATION. I AM AN ATC CTLR AT ZME. OLV IS TOO BUSY TO BE AN UNCTLED ARPT. IN MY SHORT TENURE FLYING AT OLV; I HAVE OBSERVED THAT ABOUT 1/2 OF THE NON-STUDENT PLTS FOLLOW NO ESTABLISHED PROCS OR TRADITIONS. THE STUDENTS FOLLOW; OR AT LEAST TRY TO FOLLOW; FAA RECOMMENDED PROCS. SOME OWNER PLTS DO WHAT EVER THEY WANT; SAFETY AND ORDER NOTWITHSTANDING. WITH THE VERY HIGH VOLUME OF TFC AT OLV; A CTLR IS ESSENTIAL. PLEASE COMPLETE THE ALREADY PLANNED TWR SOON!