Narrative:

At the time of the near midair collision, we were on a radar vector with clearance to descend to 11000 ft. At about 120000 at TCASII TA sounded which rapidly warned 'reduce descent.' I observed another aircraft well below us on a converging course. I thought this was the TCASII target. The first officer was talking to approach control which confirmed we were cleared to 11000. TCASII then warned 'climb.' a climb was initiated immediately. Within 5 seconds and about 100-200 ft increase in altitude, a single engine low wing blue and white aircraft passed directly below us in the opposite direction. I think he was about 300 ft below us. We were never advised of this aircraft. TCASII probably prevented a midair. We advised approach control of the climb and evasive action, and he confirmed we were clear of it, and gave us a turn to avoid the converging aircraft. Approach control was very busy at the time. Supplemental information from acn 215214: PF observed a regional carrier turboprop aircraft to our left and below on a converging course, and assumed he had traffic in sight. Flight engineer relayed the climb command to PF who then added power and climbed. PF then observed a single engine low wing GA aircraft pass directly below us about 200-400 ft vertical separation 180 degree opposite course. No traffic call from approach control. In fact, approach then gave a call to an incorrect call sign for us to turn right about 60 degrees. By now the regional carrier turboprop aircraft was still converging, and we were becoming concerned about it. Approach control then issued a turn to us using the proper call sign and also turned the regional carrier turboprop aircraft away from us.

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Original NASA ASRS Text

Title: AN MLG CREW RESPONDED TO A TCASII COMMAND TO 'CLB.' THEY DID, AND MISSED AN SMA BY ABOUT 300 FT.

Narrative: AT THE TIME OF THE NMAC, WE WERE ON A RADAR VECTOR WITH CLRNC TO DSND TO 11000 FT. AT ABOUT 120000 AT TCASII TA SOUNDED WHICH RAPIDLY WARNED 'REDUCE DSCNT.' I OBSERVED ANOTHER ACFT WELL BELOW US ON A CONVERGING COURSE. I THOUGHT THIS WAS THE TCASII TARGET. THE FO WAS TALKING TO APCH CTL WHICH CONFIRMED WE WERE CLRED TO 11000. TCASII THEN WARNED 'CLB.' A CLB WAS INITIATED IMMEDIATELY. WITHIN 5 SECONDS AND ABOUT 100-200 FT INCREASE IN ALT, A SINGLE ENG LOW WING BLUE AND WHITE ACFT PASSED DIRECTLY BELOW US IN THE OPPOSITE DIRECTION. I THINK HE WAS ABOUT 300 FT BELOW US. WE WERE NEVER ADVISED OF THIS ACFT. TCASII PROBABLY PREVENTED A MIDAIR. WE ADVISED APCH CTL OF THE CLB AND EVASIVE ACTION, AND HE CONFIRMED WE WERE CLR OF IT, AND GAVE US A TURN TO AVOID THE CONVERGING ACFT. APCH CTL WAS VERY BUSY AT THE TIME. SUPPLEMENTAL INFO FROM ACN 215214: PF OBSERVED A REGIONAL CARRIER TURBOPROP ACFT TO OUR L AND BELOW ON A CONVERGING COURSE, AND ASSUMED HE HAD TFC IN SIGHT. FLT ENGINEER RELAYED THE CLB COMMAND TO PF WHO THEN ADDED PWR AND CLBED. PF THEN OBSERVED A SINGLE ENG LOW WING GA ACFT PASS DIRECTLY BELOW US ABOUT 200-400 FT VERT SEPARATION 180 DEG OPPOSITE COURSE. NO TFC CALL FROM APCH CTL. IN FACT, APCH THEN GAVE A CALL TO AN INCORRECT CALL SIGN FOR US TO TURN R ABOUT 60 DEGS. BY NOW THE REGIONAL CARRIER TURBOPROP ACFT WAS STILL CONVERGING, AND WE WERE BECOMING CONCERNED ABOUT IT. APCH CTL THEN ISSUED A TURN TO US USING THE PROPER CALL SIGN AND ALSO TURNED THE REGIONAL CARRIER TURBOPROP ACFT AWAY FROM US.

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.