Narrative:

ATIS was calling for low scattered with approximately 6000' ceiling, 5 mi visibility, ILS approachs 16 is use. Air carrier X was being vectored by approach control, we assumed we were being vectored for the ILS because of the ATIS. (Approach never clarified). We were on a 120 degree heading at 7000'. We were given a turn to 070 degree and descend to 4000'. We started to descend to 4000' when I noticed first officer was turning to 170 degree heading (I pointed out read back 070 degree). The first officer started to turn to 070 degree after I pointed out we should be 070 degree. I called approach for a clarification. I looked out to our 9 O'clock position and saw air carrier Y at our altitude (5000'). We were descending through. We turned back south while I tried to call approach for clarification. Approach kept calling the air carrier Y call sign but our flight number, he was obviously confused. During this confusion we were able to pick out the airport visly and when the confusion subsided we informed approach we had the airport. We were cleared for a visibility runway 16R and air carrier Y was cleared visibility runway 16L. I called the supervisor after our landing. He apologized for the confusion and said he was expecting our call. He said the controller had transposed our call signs and was giving our instructions to air carrier Y and vice-versa. He explained the controller was experienced but just got confused and was corrected by the controller sitting next to him. Good thing we were visibility and saw the other traffic. Our horizontal sep was less than 1000'. I have no doubt that if we were IMC we would have collided.

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Original NASA ASRS Text

Title: ACR X HAD LESS THAN STANDARD SEPARATION FROM ACR Y. SYSTEM ERROR.

Narrative: ATIS WAS CALLING FOR LOW SCATTERED WITH APPROX 6000' CEILING, 5 MI VISIBILITY, ILS APCHS 16 IS USE. ACR X WAS BEING VECTORED BY APCH CTL, WE ASSUMED WE WERE BEING VECTORED FOR THE ILS BECAUSE OF THE ATIS. (APCH NEVER CLARIFIED). WE WERE ON A 120 DEG HDG AT 7000'. WE WERE GIVEN A TURN TO 070 DEG AND DSND TO 4000'. WE STARTED TO DSND TO 4000' WHEN I NOTICED F/O WAS TURNING TO 170 DEG HDG (I POINTED OUT READ BACK 070 DEG). THE F/O STARTED TO TURN TO 070 DEG AFTER I POINTED OUT WE SHOULD BE 070 DEG. I CALLED APCH FOR A CLARIFICATION. I LOOKED OUT TO OUR 9 O'CLOCK POS AND SAW ACR Y AT OUR ALT (5000'). WE WERE DSNDING THROUGH. WE TURNED BACK S WHILE I TRIED TO CALL APCH FOR CLARIFICATION. APCH KEPT CALLING THE ACR Y CALL SIGN BUT OUR FLT NUMBER, HE WAS OBVIOUSLY CONFUSED. DURING THIS CONFUSION WE WERE ABLE TO PICK OUT THE ARPT VISLY AND WHEN THE CONFUSION SUBSIDED WE INFORMED APCH WE HAD THE ARPT. WE WERE CLRED FOR A VIS RWY 16R AND ACR Y WAS CLRED VIS RWY 16L. I CALLED THE SUPVR AFTER OUR LNDG. HE APOLOGIZED FOR THE CONFUSION AND SAID HE WAS EXPECTING OUR CALL. HE SAID THE CTLR HAD TRANSPOSED OUR CALL SIGNS AND WAS GIVING OUR INSTRUCTIONS TO ACR Y AND VICE-VERSA. HE EXPLAINED THE CTLR WAS EXPERIENCED BUT JUST GOT CONFUSED AND WAS CORRECTED BY THE CTLR SITTING NEXT TO HIM. GOOD THING WE WERE VIS AND SAW THE OTHER TFC. OUR HORIZ SEP WAS LESS THAN 1000'. I HAVE NO DOUBT THAT IF WE WERE IMC WE WOULD HAVE COLLIDED.

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.