NMAC -- IN IMC ON LOC.

Narrative

WE WERE ON THE ZIGGY 3 ARR INTO ONT. WX WAS 3000 FT BROKEN WITH TOPS ABOUT 10000 FT. APCH CTL'S PRIMARY RADAR WAS OUT AND HE WAS GETTING A SECONDARY FEED FROM CTR WHICH HAD A CONSIDERABLE DELAY FOR MODE C INFO. WE WERE DSNDED TO 8000 FT AND VECTORED ACROSS THE LOC AND THEN TURNED 180 DEG BACK TO THE N. AS WE WERE XING THE LOC THE FIRST TIME WE HEARD ANOTHER AIRLINE FLT GIVEN TFC AND A SUBSEQUENT RA (TCASII) AND FURTHER CONVERSATION WITH THE CTLR ABOUT A NEAR MISS AND AT THE SAME TIME I OBSERVED THE EVENT ON OUR TCASII EHSI. THE 2 TARGETS MERGED AT 5000 FT ABOUT 2 MI E OF PETIS ON THE LOC. AS WE PROCEEDED S THROUGH THE LOC AND WERE VECTORED BACK N THE INTRUDER ACFT CONTINUED CLBING AND PROCEEDING E; GENERALLY OUT THE RWY 26L LOC AND UP THE GS. WE TURNED AS HE TURNED AND WE WERE ISSUED TFC BY THE CTLR WITH A 300-400 FT LAG ON TCASII READOUT OF HIS ALT AND WHAT THE CTLR WAS SEEING. THE TCASII 'TA' WAS INTERRUPTED BY THE TCASII RA 'DSND XING DSND.' WE DSNDED ABOUT 500 FT AND CAUGHT A GLIMPSE OF THE ACFT THROUGH A SMALL BREAK IN THE CLOUDS. IN MY OPINION THERE WAS NO WAY THIS ACFT WAS KEEPING VFR CLOUD SEPARATION. HE WAS TRYING TO CLB OUT TO GET ON TOP BY TRACKING OUT A VERY BUSY ILS. THE INTRUDER WAS PROBABLY A SINGLE ENG (POSSIBLY LIGHT TWIN) WITH A T-TAIL. I FILED A NEAR MID-AIR RPT SO THAT AN INVESTIGATION WOULD BE PURSUED.