Narrative:

Air carrier X on vector for approach to slc at approximately 13000 ft, the TCASII called out 'traffic' followed shortly by 'descend, descend.' we acquired visual contact on the other aircraft, air carrier Y, as we initiated a descent and flew under air carrier Y. We notified approach of the conflict and diversionary tactics. Approach said that they saw no traffic until just that instant that we called. There seemed to be much confusion on this descent and arrival into the slc area with numerous speed (increase -- slow down) changes and heading changes. The controller later told us that we passed within 100 ft vertical and less than a mi horizontal from air carrier Y. Supplemental information from acn 263638: we got a TCASII alert of 'traffic, traffic' followed instantly by 'descend, descend.' at this time I started a descent and just then we had visual contact of the intruding aircraft at 11:30 position, level, approximately 1 mi. I immediately started a right turn while descending and easily avoided the intruding aircraft. We were given a heading to 030 degrees/descend to 8000 ft. We continued to slc and landed. I called and talked to approach control supervisor and was informed the intruder was VFR off ogden airport. They did not have radar contact. Today I found out from company safety that the aircraft was a metroliner, was talking to ATC, in fact receiving an IFR clearance and he was actually off from ogden airport.

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Original NASA ASRS Text

Title: 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.

Data retrieved from NASA's ASRS site as of July 2007 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.