NMAC; TCASII RA.

Narrative

VFR CONDITIONS. CLRED FROM OVER CEDES INTXN HDG 230 DEGS DSND FROM 11000 FT TO 7000 FT AT 170 KTS. PASSING 9500 FT RECEIVED TA ON TCASII. CAPT FLYING; FO LOOKED TO R AND SAW KING AIR BELOW AND AT TIME PARALLELING COURSE. AT 9100 FT GOT RA AND FO LOOKED OUT TO R AND KING AIR HAD TURNED DIRECTLY TOWARDS US. FO CALLED FOR AN IMMEDIATE LEVEL OFF. I DISCONNECTED AUTOPLT AND LEVELED ACFT AT 9000 FT. KING AIR PASSED DIRECTLY BELOW US AT 8500 FT. I SAW ACFT APPEAR AS IT CAME IN VIEW FROM MY L WINDOW. HAD DSCNT CONTINUED THERE WOULD HAVE BEEN A COLLISION. FO IMMEDIATELY CONTACTED APCH CTL ASKING ABOUT TFC. APCH SEEMED VAGUE ABOUT WHO IT WAS. THE KING AIR MUST HAVE BEEN MONITORING THE FREQ. HE RESPONDED TO APCH'S QUESTIONING HIS LOCATION AND SAID; 'I HAD XX IN SIGHT.' I DON'T THINK HE WAS AWARE OF OUR IMMEDIATE ACTION OF STOPPING OUR 1800-2000 FPM RATE OF DSCNT TO AVOID COLLISION. I CONTACTED APCH CTL SUPVR UPON ARR AT SFO. HE HAD ALREADY SPOKEN TO CTLR AND APPARENTLY KING AIR WAS VFR. CTLR WAS WORKING US AND AN ACFT DIRECTLY BELOW US AND AS KING AIR GOT CLOSE TO BEING BTWN BOTH OURSELVES AND LOWER ALT ACFT; HE BLENDED IN ON CTLR'S SCOPE. SUPVR APOLOGIZED AND SAID HE HAD NO REAL ANSWERS ONE BECOMES CONFIDENT AND TRUSTING WHEN BEING CTLED INTO AN ARPT OF THE SIZE OF SFO. WE RELY ON TFC SEPARATION. IT IS ALSO A TIME THAT IS VERY BUSY FOR FLC -- SETTING UP FMS; FINAL APCH BRIEFINGS; CHKLISTS; MONITORING APCH FREQS TO HEAR WHAT OTHER ACFT ARE DOING. THANKS TO A DILIGENT AND OBSERVANT FO AND TCASII; THIS POTENTIAL COLLISION WAS AVOIDED. SUGGESTIONS: WHEN VFR TFC IN ARR AREA AS THIS; APCH SHOULD TRY TO CONTACT AND ADVISE OF DSNDING TFC AND/OR DO NOT DSND ARRIVING TFC THROUGH VFR TFC UNTIL CLR AND/OR PUT ARR IN THE TCA TO AVOID THIS TYPE OF CONFLICT/OR MAKE IT AN ARR CORRIDOR WITHIN TCA.