Narrative:

We were being vectored to approach for runway 4R at bos descending to 6000 ft and were told by approach to stop descent at 7000 ft and turn to 230 degree heading. We were IMC and noticed a target on the TCASII at 12 O'clock position at 6500 ft. TCASII target then continued to climb towards our altitude and remained on a collision course with us. TCASII target changed from white to yellow as we then turned further west to avoid it. Approach told other aircraft Y to descend back to 6500 ft immediately. TCASII target continued to close climbing to 200 ft below our altitude and went to a red RA. We climbed at 1500 FPM as recommended by TCASII RA and the target passed under us so close that the aircraft symbol on our TCASII screen blocked out the target symbol. We climbed about 200 ft, the aircraft passed under and behind us, and the TCASII informed us that we were clear of conflict. We informed approach of our turn and climb, and returned to our assigned heading and altitude. We never saw the other plane as we were in the clouds during the entire event.

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Original NASA ASRS Text

Title: WHILE DSNDING FOR AN APCH TO BOS, AN ACR FLC WAS INSTRUCTED BY ATC TO STOP DSCNT AND TURN BECAUSE OF TFC.

Narrative: WE WERE BEING VECTORED TO APCH FOR RWY 4R AT BOS DSNDING TO 6000 FT AND WERE TOLD BY APCH TO STOP DSCNT AT 7000 FT AND TURN TO 230 DEG HDG. WE WERE IMC AND NOTICED A TARGET ON THE TCASII AT 12 O'CLOCK POS AT 6500 FT. TCASII TARGET THEN CONTINUED TO CLB TOWARDS OUR ALT AND REMAINED ON A COLLISION COURSE WITH US. TCASII TARGET CHANGED FROM WHITE TO YELLOW AS WE THEN TURNED FURTHER W TO AVOID IT. APCH TOLD OTHER ACFT Y TO DSND BACK TO 6500 FT IMMEDIATELY. TCASII TARGET CONTINUED TO CLOSE CLBING TO 200 FT BELOW OUR ALT AND WENT TO A RED RA. WE CLBED AT 1500 FPM AS RECOMMENDED BY TCASII RA AND THE TARGET PASSED UNDER US SO CLOSE THAT THE ACFT SYMBOL ON OUR TCASII SCREEN BLOCKED OUT THE TARGET SYMBOL. WE CLBED ABOUT 200 FT, THE ACFT PASSED UNDER AND BEHIND US, AND THE TCASII INFORMED US THAT WE WERE CLR OF CONFLICT. WE INFORMED APCH OF OUR TURN AND CLB, AND RETURNED TO OUR ASSIGNED HDG AND ALT. WE NEVER SAW THE OTHER PLANE AS WE WERE IN THE CLOUDS DURING THE ENTIRE EVENT.

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.