FLC OF AN MLG DSNDED FOR APCH AT THE WRONG ARPT DURING NIGHT TIME OPS RESULTING IN PENETRATION OF ANOTHER ATA (CLASS D AIRSPACE).

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WE WERE AT 3000 FT BEING VECTORED FOR AN ILS TO RWY 31 AT BNA TO MAINTAIN 2600 FT UNTIL ESTABLISHED ON THE LOC. THE FO WAS FLYING AND AS HIS LOC CAME ALIVE I TUNED THE #1 VOR FROM THE BNA VOR TO THE BNA RWY 31 ILS. WE WERE VISUAL AT THIS POINT AND THE RWY WAS IN SIGHT ALONG WITH THE VASI. WE SHOWED OM PASSAGE BUT THE INSTS SHOWED US BEING TO THE L OF THE LOC AND BELOW GS. HOWEVER; WE WERE LINED UP WITH THE RWY AND ON GS ACCORDING TO THE VASI. I RETUNED TO THE BNA VOR FOR A DME FIX. THE FO HAD STARTED TO DSND ON THE VASI. THE OVERALL PICTURE WAS NOT RIGHT AND I TOLD THE FO TO LEVEL OFF AND STOP THE DSCNT. BY THIS TIME THE DME LOCKED IN AND SHOWED APPROX 14 DME AND I REALIZED THAT THIS WAS SMYRNA ARPT NOT BNA. THE FO LEVELED OFF AT 1300 FT MSL. JUST THEN WE RECEIVED A TCASII RA SHOWING AN ACFT AHEAD; BELOW AND CLBING. AS WE HAD STARTED TO CLB THE RA WAS RESOLVED. WE CONTINUED TO CLB BACK TO ALT AND COMPLETED THE APCH TO BNA. IN THE CLB BNA CAME INTO VIEW. THE APCH AND RWY LIGHTS WERE ON AND TURNED UP HIGH AT SMYRNA AND THE RWY LINES UP WITH RWY 31 AT BNA. ALSO BNA RWY LIGHTS WERE LOW. IF THE ILS HAD NOT BEEN TUNED IN IT COULD HAVE BEEN WORSE. IT WOULD HELP IF THE BNA RWY 31 ILS HAD DME AND THE RWY LIGHTS WERE TURNED UP. I SHOULD HAVE CAUGHT THIS EARLIER AND IN THE FUTURE I WILL LEAVE THE VOR DME TUNED IN UNTIL ESTABLISHED ON THE ILS.