NMAC BTWN AN SF340 COMMUTER IN CRUISE AT 16000 FT AND A CARGO B727 FROM 15000 FT ON A VISUAL CLB THROUGH OCCUPIED ALT OF THE SF340. TCASII ON SF340 SAVED THE DAY IN THIS NIGHT OP.

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OUR SAAB 340 WAS LEVEL AT 16000 FT NBOUND TO MKE. ATC ISSUED OPPOSITE DIRECTION TFC AT 15000 FT; A SWBOUND CARGO B727 FLT AT 15000 FT. WE TURNED OUR LNDG LIGHT ON AND THE B727 CALLED TFC IN SIGHT. ATC THEN ISSUED A VISUAL CLB CLRNC THROUGH OUR ALT TO THE CARGO B727 WHO WAS AT APPROX 6-7 MI ON OUR TCASII. WE COULD SEE HE STARTED HIS CLB; AND HIS LIGHT POINTED AT US. SECONDS LATER OUR TCASII ISSUED AN RA TO 'DSND; DSND NOW.' I RESPONDED TO THE RA IMMEDIATELY. AND AS QUICKLY AS I DID; THE B727 PASSED OVERHEAD. I REMEMBER MY TCASII INDICATING HIS ALT AS A +400 FT. WE COMPLETED OUR DSCNT TO 15400 FT THEN RPTED OUR DEV TO ATC AND CLBED TO ASSIGNED ALT. RECOMMEND: 1) ELIMINATE VISUAL CLB OR DSCNT CLRNCS; OR 2) ONLY ISSUE THESE CLRNCS TO ACFT HAVING TCASII; OR 3) HAVE ATC ISSUE VECTORS TO MAKE SURE ACFT MISS EACH OTHER. TCASII HELPED US MAKE THE CORRECT EVASIVE ACTION! THE HUMAN EYE COULD NOT DETECT HIS MOVEMENT; SPD OR RATE OF ASCENT. SUPPLEMENTAL INFO FROM ACN 356082: WE DISCUSSED THE SIT WITH CTR AND HE APOLOGIZED FOR THE CLOSE ENCOUNTER. WE RETURNED TO 16000 FT. WHEN I LAST LOOKED AT TCASII; WE WERE 400 FT APART. AT THAT POINT MY EYES WENT OUT THE WINDOW IN CASE I NEEDED TO DEMAND A L TURN TO AVOID HIM. HOWEVER; I DIDN'T GRAB THE CTLS OR COMMAND A TURN SINCE I SAW WE WERE CLR. I FEEL WE WERE ONLY A FEW HUNDRED FT APART AND WAY TOO CLOSE. I DON'T FEEL THE B727 EVER SAW US SINCE HE TOOK NO EVASIVE ACTION. I FEEL CTLRS SHOULD NOT ALLOW VISUAL CLBS WHEN THERE IS 600 KTS CLOSURE IN A NIGHT SIT HEAD ON. IT IS EASY TO CONFUSE TFC WITH OTHER TFC; STARS; ETC; AT NIGHT. ALSO; SINCE HE WASN'T EQUIPPED WITH TCASII; THIS CREATED MORE CONFLICT.