Narrative:

I was captain of abc flight talking to chicago approach control at 7000 ft, heading 310 degrees, speed 170 KTS on downwind to runway 14R at ord. Xyz flight was somewhere ahead on downwind. At a point approximately 5 mi south of ord, approach said 'abc turn right to 050 degrees, descend to 4000 ft.' I repeated the clearance and called out of 7000 ft for 4000 ft. At approximately 5600 ft in the descent on a 050 degree heading, we received a TCASII RA. The traffic was indicated at 2 O'clock, 1 mi and 400 ft low. We responded to the climb advisory and called out our diversion. Approach said 'you should be at 7000 ft heading 310 degrees.' I replied that I had read back the clearance directed to abc and that we had a traffic problem. After leveling at 7000 ft and a 310 degree heading, approach said 'abc turn right 050 degrees.' this clearance was immediately challenged by us. Approach said 'abc fly heading 310 degrees, 7000 ft.' approach then gave a 050 degree heading to xyz flight. I feel our original clearance to 050 degrees and 4000 ft was meant for xyz flight. I believe this incident was caused by: 1) controller error. 2) controller workload. 3) similar sounding call signs, and 4) my failure to immediately question a clearance which 'didn't seem right' for ord. I now, also, am a believer in TCASII. Supplemental information from acn 249361: in later conversation with captain on xyz, we confirmed that the controller was switching our call signs in error.

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Original NASA ASRS Text

Title: APCH CTLR SWITCHES CALL SIGNS RESULTING IN TCASII RA.

Narrative: I WAS CAPT OF ABC FLT TALKING TO CHICAGO APCH CTL AT 7000 FT, HDG 310 DEGS, SPD 170 KTS ON DOWNWIND TO RWY 14R AT ORD. XYZ FLT WAS SOMEWHERE AHEAD ON DOWNWIND. AT A POINT APPROX 5 MI S OF ORD, APCH SAID 'ABC TURN R TO 050 DEGS, DSND TO 4000 FT.' I REPEATED THE CLRNC AND CALLED OUT OF 7000 FT FOR 4000 FT. AT APPROX 5600 FT IN THE DSCNT ON A 050 DEG HDG, WE RECEIVED A TCASII RA. THE TFC WAS INDICATED AT 2 O'CLOCK, 1 MI AND 400 FT LOW. WE RESPONDED TO THE CLB ADVISORY AND CALLED OUT OUR DIVERSION. APCH SAID 'YOU SHOULD BE AT 7000 FT HDG 310 DEGS.' I REPLIED THAT I HAD READ BACK THE CLRNC DIRECTED TO ABC AND THAT WE HAD A TFC PROB. AFTER LEVELING AT 7000 FT AND A 310 DEG HDG, APCH SAID 'ABC TURN R 050 DEGS.' THIS CLRNC WAS IMMEDIATELY CHALLENGED BY US. APCH SAID 'ABC FLY HDG 310 DEGS, 7000 FT.' APCH THEN GAVE A 050 DEG HDG TO XYZ FLT. I FEEL OUR ORIGINAL CLRNC TO 050 DEGS AND 4000 FT WAS MEANT FOR XYZ FLT. I BELIEVE THIS INCIDENT WAS CAUSED BY: 1) CTLR ERROR. 2) CTLR WORKLOAD. 3) SIMILAR SOUNDING CALL SIGNS, AND 4) MY FAILURE TO IMMEDIATELY QUESTION A CLRNC WHICH 'DIDN'T SEEM RIGHT' FOR ORD. I NOW, ALSO, AM A BELIEVER IN TCASII. SUPPLEMENTAL INFORMATION FROM ACN 249361: IN LATER CONVERSATION WITH CAPT ON XYZ, WE CONFIRMED THAT THE CTLR WAS SWITCHING OUR CALL SIGNS IN ERROR.

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.