B737 CPR PLT RESPONDS TO TCASII AND SCT TFC ALERT WHEN DSNDING INTO VNY.

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WE WERE ON RADAR VECTORS TO INTERCEPT LOC RWY 16R AT VNY AND CLRED TO DSND TO 6000 FT; CLRED FOR APCH. PASSING 7000 FT AND AS WE WERE INTERCEPTING LOC; OUTSIDE KADIE INTXN; BUT INSIDE UMBER FIX; SOCAL CALLED TFC AT 11 O'CLOCK POS. SOCAL LEVELED US AT 6000 FT AND SAID TFC WAS NOT IN CONTACT WITH THEM. AS OUR ACFT INTERCEPTED LOC; I SAW THE TFC PASS UNDER OUR NOSE. THE TFC; A LIGHT TWIN; APPEARED TO BE ALSO INTERCEPTING THE LOC UNDER US. A FEW SECONDS LATER; OUR TCASII SOUNDED AN RA 'MONITOR VERT SPD.' AFTER COMPLYING WITH THE RA; WE PASSED THE LOM (KADIE) ABOUT 1 DOT HIGH ON THE GS. AFTER THE RA CLRED; I INCREASED DSCNT TO CAPTURE THE GS. A FEW SECONDS LATER; THE TCASII SHOWED THE TFC 600 FT BELOW AND SLIGHTLY BEHIND AND THEN WE GOT A SECOND TCASII RA 'MONITOR VERT SPD' REQUIRING A SECOND DECREASE IN DSCNT RATE. AFTER WE LANDED; WE ASKED TWR ABOUT THE OTHER ACFT. WE WERE TOLD THAT IT WAS A SENECA. IT WAS NOT IN CONTACT WITH SOCAL APCH AND HAD JUST CONTACTED TWR AFTER IT PASSED UNDER US. THIS INCIDENT SOUNDS VERY CLOSE TO WHAT HAPPENED DURING THE MIDAIR A FEW YRS AGO AT VNY. DIFFERENT PROCS NEED TO BE DEVELOPED TO SEPARATE IFR AND VFR TFC APCHING VNY FROM THE N. AT LEAST THE REQUIREMENT THAT ALL TFC BE IN CONTACT WITH SOCAL BEFORE XING 15 DME FROM THE VNY VOR. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: RPTR ADVISED THAT HE IS VERY FAMILIAR WITH VNY AND THIS WAS HIS FIRST 'CLOSE' EVENT.