ACR X TCASII TA RA HAD LTSS FROM ACR Y. SYS ERROR.

Narrative

ACR X ON VECTOR FOR APCH TO SLC AT APPROX 13000 FT; THE TCASII CALLED OUT 'TFC' FOLLOWED SHORTLY BY 'DSND; DSND.' WE ACQUIRED VISUAL CONTACT ON THE OTHER ACFT; ACR Y; AS WE INITIATED A DSCNT AND FLEW UNDER ACR Y. WE NOTIFIED APCH OF THE CONFLICT AND DIVERSIONARY TACTICS. APCH SAID THAT THEY SAW NO TFC UNTIL JUST THAT INSTANT THAT WE CALLED. THERE SEEMED TO BE MUCH CONFUSION ON THIS DSCNT AND ARR INTO THE SLC AREA WITH NUMEROUS SPD (INCREASE -- SLOW DOWN) CHANGES AND HDG CHANGES. THE CTLR LATER TOLD US THAT WE PASSED WITHIN 100 FT VERT AND LESS THAN A MI HORIZ FROM ACR Y. SUPPLEMENTAL INFO FROM ACN 263638: WE GOT A TCASII ALERT OF 'TFC; TFC' FOLLOWED INSTANTLY BY 'DSND; DSND.' AT THIS TIME I STARTED A DSCNT AND JUST THEN WE HAD VISUAL CONTACT OF THE INTRUDING ACFT AT 11:30 POS; LEVEL; APPROX 1 MI. I IMMEDIATELY STARTED A R TURN WHILE DSNDING AND EASILY AVOIDED THE INTRUDING ACFT. WE WERE GIVEN A HDG TO 030 DEGS/DSND TO 8000 FT. WE CONTINUED TO SLC AND LANDED. I CALLED AND TALKED TO APCH CTL SUPVR AND WAS INFORMED THE INTRUDER WAS VFR OFF OGDEN ARPT. THEY DID NOT HAVE RADAR CONTACT. TODAY I FOUND OUT FROM COMPANY SAFETY THAT THE ACFT WAS A METROLINER; WAS TALKING TO ATC; IN FACT RECEIVING AN IFR CLRNC AND HE WAS ACTUALLY OFF FROM OGDEN ARPT.