Narrative:

In this situation, I was captain performing the duties of PNF, on a 2 person crew. We were cruising at FL290, and requested climb to FL330. Our call sign was air carrier xy. It is important to note that air carrier Y was also on frequency. We had acknowledged the presence of air carrier Y and air carrier Y had acknowledged our presence with respect to like call signs. When I initially requested climb from FL290, ZDV responded that we could expect the climb, and that some vectoring would be required. Soon, we were cleared to climb. A min or so later, ATC instructed air carrier Y to turn to a heading. Air carrier Y responded and turned. We saw air carrier Y above our altitude, ahead of us, and in the same direction of flight. At least 2 more instructions were then directed to air carrier Y. Turn further to a heading, and to increase the rate of turn. All radio traffic had sounded very routine to this point. Then I noticed a yellow diamond symbol on the TCASII screen (12 O'clock, minus 300 ft) at about the time ATC told air carrier Y to increase rate of turn. At that moment, I realized that the turns were actually intended for us air carrier xy. I requested instructions from ATC, but was blocked. Then our TCASII issued an RA. My copilot complied, increasing our rate of climb. We had visually acquired the approaching head-on traffic by this time, and my copilot turned to the right, to increase the separation distance. The RA cleared before we leveled at 330. I am virtually certain that ATC issued instructions to the wrong aircraft, but similar sounding call signs played a significant role in this incident, in spite of the fact that both aircrews and the controller were well aware of the potential hazard. I don't believe a midair collision was imminent, but TCASII probably prevented the incident from developing into a near midair collision.

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Original NASA ASRS Text

Title: SIMILAR CALL SIGNS ACR XY CLB THROUGH OCCUPIED ALT TCASII RA HAD LTSS FROM ACR Y. SYS ERROR.

Narrative: IN THIS SIT, I WAS CAPT PERFORMING THE DUTIES OF PNF, ON A 2 PERSON CREW. WE WERE CRUISING AT FL290, AND REQUESTED CLB TO FL330. OUR CALL SIGN WAS ACR XY. IT IS IMPORTANT TO NOTE THAT ACR Y WAS ALSO ON FREQ. WE HAD ACKNOWLEDGED THE PRESENCE OF ACR Y AND ACR Y HAD ACKNOWLEDGED OUR PRESENCE WITH RESPECT TO LIKE CALL SIGNS. WHEN I INITIALLY REQUESTED CLB FROM FL290, ZDV RESPONDED THAT WE COULD EXPECT THE CLB, AND THAT SOME VECTORING WOULD BE REQUIRED. SOON, WE WERE CLRED TO CLB. A MIN OR SO LATER, ATC INSTRUCTED ACR Y TO TURN TO A HDG. ACR Y RESPONDED AND TURNED. WE SAW ACR Y ABOVE OUR ALT, AHEAD OF US, AND IN THE SAME DIRECTION OF FLT. AT LEAST 2 MORE INSTRUCTIONS WERE THEN DIRECTED TO ACR Y. TURN FURTHER TO A HDG, AND TO INCREASE THE RATE OF TURN. ALL RADIO TFC HAD SOUNDED VERY ROUTINE TO THIS POINT. THEN I NOTICED A YELLOW DIAMOND SYMBOL ON THE TCASII SCREEN (12 O'CLOCK, MINUS 300 FT) AT ABOUT THE TIME ATC TOLD ACR Y TO INCREASE RATE OF TURN. AT THAT MOMENT, I REALIZED THAT THE TURNS WERE ACTUALLY INTENDED FOR US ACR XY. I REQUESTED INSTRUCTIONS FROM ATC, BUT WAS BLOCKED. THEN OUR TCASII ISSUED AN RA. MY COPLT COMPLIED, INCREASING OUR RATE OF CLB. WE HAD VISUALLY ACQUIRED THE APCHING HEAD-ON TFC BY THIS TIME, AND MY COPLT TURNED TO THE R, TO INCREASE THE SEPARATION DISTANCE. THE RA CLRED BEFORE WE LEVELED AT 330. I AM VIRTUALLY CERTAIN THAT ATC ISSUED INSTRUCTIONS TO THE WRONG ACFT, BUT SIMILAR SOUNDING CALL SIGNS PLAYED A SIGNIFICANT ROLE IN THIS INCIDENT, IN SPITE OF THE FACT THAT BOTH AIRCREWS AND THE CTLR WERE WELL AWARE OF THE POTENTIAL HAZARD. I DON'T BELIEVE A MIDAIR COLLISION WAS IMMINENT, BUT TCASII PROBABLY PREVENTED THE INCIDENT FROM DEVELOPING INTO A NMAC.

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.