MLG HAS TCASII RA ON APCH; RESPONDS.

Narrative

RECEIVED A POP-UP TARGET ON TCASII AT LEVEL-OFF 6000 FT MSL ON GEETR ARR. 15 DME FROM BNA; TARGET WAS 11 O'CLOCK 2-3 MI 100 FT BELOW -- CONVERGING PATH. WE IMMEDIATELY RECEIVED A 'TA;' AND APPROX 5 SECONDS LATER AN 'RA' TO CLB AT APPROX 3000 FPM. I DID SO AND 10 SECONDS LATER RECEIVED THE CLEAR OF TA. DEV WAS 800 UP AND ATC WAS ADVISED IMMEDIATELY. THE CTLR SAID TFC PASSED OUR L SIDE BY A MI AND HE WAS NOT IN CONTACT WITH HIM. WE NEVER SAW HIM. NO FURTHER INCIDENT FOR REMAINDER OF FLT. NO TIME TO ADVISE PAX OR CABIN CREW ON THE NOTICEABLE EVASION ACTION. CALLED ATC ON THE PHONE LATER; THEY WERE UNCONCERNED WITH THE DEV SINCE OUR DEV DID NOT CREATE A CONFLICT AND WAS MOMENTARY IN NATURE. HE FIGURED IT WAS VFR TFC IN 'UNPROTECTED AIRSPACE;' AND SAID ATC WAS TOO BUSY TO NOTICE THE TARGET. UNDERSTANDABLY; IT IS A 'TIME PERMITTING' FUNCTION OF ATC IN THIS CASE; BUT CONSIDERING OUR CLOSE PROX TO THE ARPT; AND OUR ALT ON THE STAR; WHY AREN'T WE PROTECTED BY A TCA? AFTER ALL; IT IS A HUB FOR MY CARRIER WITH MULTIPLE COMPLEXES. THANK GOODNESS FOR OUR TCASII FOR ALL ITS SHORTCOMINGS; IT MIGHT HAVE PREVENTED A MAJOR MISHAP ON THIS BEAUTIFULLY CLR DAY.