ACR X TCASII TA RA EVASIVE ACTION TAKEN HAD NMAC WITH SMA. SEE AND AVOID CONCEPT.

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ON 11/91; ACR X WAS INVOLVED IN A NMAC WITH AN SMA WHILE ON FINAL APCH TO SAN JOSE INTL ARPT. THE INCIDENT TOOK PLACE ABOUT 7 NM FROM TOUCHDOWN WHILE CONDUCTING AN ILS APCH TO RWY 30L. WHILE INBOUND ON FINAL APCH AND WHILE STILL COMMUNICATING WITH BAY APCH CTL. APCH CTLR AND OUR COCKPIT CREW WERE EXTREMELY BUSY AT THIS STAGE OF THE FLT. THE SMA ACFT IN QUESTION WAS NOT IDENTED AS POTENTIAL TFC EITHER BY BAY APCH CTL OR THE SAN JOSE TWR. IMMEDIATELY AFTER THE HDOF TO THE TWR; THE NMAC TOOK PLACE. THE FIRST INDICATION WAS A TCASII TA; FOLLOWED IMMEDIATELY BY A RA. THE TCASII TARGET WAS RED. THE FO; WHO WAS FLYING; REACTED IMMEDIATELY; FOLLOWING THE RECOMMENDED EVASIVE ACTION DISPLAYED ON THE TCASII VSI. THE SMA PASSED FROM R TO L. THE ONLY ALT INFO I RECALL INDICATED THE ACFT WAS 500 FT BELOW US. I DID NOT HAVE TIME TO NOTICE THE VSI DISPLAY. INSTEAD; I IMMEDIATELY DIRECTED MY ATTN TO THE TARGET ACFT. I ACQUIRED VISUAL CONTACT WITH THE ACFT JUST AS IT WAS PASSING BENEATH THE NOSE OF OUR AIRPLANE. THE TIME BTWN TCASII ALERT AND MY LOOSING SIGHT OF THE TARGET ACFT WAS LESS THEN 5 SECONDS. UPON CONTACTING THE TWR FOR THE FIRST TIME; I IMMEDIATELY NOTIFIED THEM OF THE INCIDENT. ADVISING THEM OF THE CLOSE PROX OF THE TFC. SUPPLEMENTAL INFO FROM ACN 194513. WE HAD TCASII IN THE MLG AND IT WAS ON IN THE RA MODE . THE VISIBILITY WAS OK WITH SOMEWHAT HAZY CONDITIONS. AT ABOUT 8 MI OR SO OUT THE TCASII ALERTED US TO A TA AND WE GOT AN RA WHICH STATED 'MONITOR VERT DSCNT.' THE VSI WHICH I SCANNED NEXT SHOWED ME THAT I NEEDED TO ALMOST LEVEL OFF. AT THE TIME I WAS HAND FLYING THE ACFT AND WE WERE EXACTLY ON GS AND LOC BEAM WITH ABOUT A 1300 FT RATE OF DSCNT. AS SOON AS THE RA WENT OFF I BEGAN T SLOWLY ADD PWR AND LEVEL THE ACFT. AT THE SAME TIME I ASKED THE CAPT IF THIS ALERT WAS FOR REAL AND DID HE SEE ANYTHING IN FRONT OF US AS I DID NOT SEE ANY ACFT. THE CAPT REFERENCED THE TCASII SCOPE TO SEE WHAT POS THE TARGET WAS COMING FROM AND AS HE THEN TURNED OUTSIDE TO LOOK FOR IT THE TCASII TOLD ME TO 'CLB NOW CLB.' I ADDED PWR TO ABOUT 1.7 EPR AND PUT THE ACFT IN ABOUT 800 FPM CLB (AS PER THE VSI LIGHTS). THE CAPT THEN GOT SIGHT OF THE SINGLE ENG ACFT XING OUR FLT PATH FROM R TO L AND WE KEPT VISUAL SEPARATION FROM IT. AS WE FLEW R OVER THE ACFT THE TCASII SHOWED 500 FT SEPARATION AND I WAS 1 1/2 DOT ABOVE GS. NO MENTION OF THIS ACFT (WHO HAD AN OPERABLE TRANSPONDER WITH MODE C) WAS MADE BY APCH CTL OR SAN JOSE TWR WHICH IS WHO WE WERE CHKING IN WITH AT THE TIME. IF WE HAD NOT HAD THE TCASII AND BEEN RIGHT ON GS OR SLIGHTLY BELOW IT A COLLISION COULD HAVE BEEN POSSIBLE AS THE ACFT WAS VERY HARD TO PICK OUT. SAN JOSE APCH CORRIDOR HAS ALWAYS BEEN A HOT SPOT. THEY NEED TO HAVE TOTAL SANITATION OF THE AIRSPACE IN THE APCH CORRIDOR TO ACFT INBOUND TO SJC ONLY.