Narrative:

Inbound to phl on bunts one arrival. After bunts intersection, descended from 8000 ft to 6000 ft. Aircraft previous had complained of bad ride at 6000 ft. We asked controller for lower based on other's complaints. Controller informed us that she needed us at 6000 ft. For 15 mi we complied. In and out of cloud bases at 6000 ft, broken layer above, heading 170 degrees for downwind to base leg set up (vectored). Nearing phl airport I initiated a call for request for lower. Radio communications were tight and busy. At end of transmission for lower, I heard a broken communication for a heading to 090 degrees -- no aircraft call sign. No one acknowledged ATC's command. The directive was not issued again. I questioned approach twice as to who the heading was for with no reply. Captain (PF) stayed on 170 degree heading. Controller came back up, saying she was on land line. I questioned again (third transmission on same question). She directed us to turn hard 070 degrees -- VFR target had 'popped' up above us at 6500 ft. TCASII idented target as a TA (amber), then turned to RA (red) 'descend, descend, descend' just as the captain clicked off autoplt, banked 40 degrees left and began descent at 4000 FPM. I informed approach that we were descending out of 6000 ft on an RA. Captain stopped descent at 5300 ft after RA ceased. I informed controller that we were at 5300 ft. She replied she needed us at 6000 ft. We complied, climbed and was handed off to final controller for a non eventful landing at phl. Our best estimation is that the traffic causing the RA was 300 ft above at its lowest altitude, and as close as 400-500 ft horizontally from us.

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Original NASA ASRS Text

Title: NMAC. FLC OF AN MLG DSNDED FROM ASSIGNED ALT IN RESPONSE TO A TCASII RA DURING A STAR ARR. THE OTHER UNKNOWN ACFT CAME WITHIN 300 FT OF THE RPTR'S ACFT.

Narrative: INBOUND TO PHL ON BUNTS ONE ARR. AFTER BUNTS INTXN, DSNDED FROM 8000 FT TO 6000 FT. ACFT PREVIOUS HAD COMPLAINED OF BAD RIDE AT 6000 FT. WE ASKED CTLR FOR LOWER BASED ON OTHER'S COMPLAINTS. CTLR INFORMED US THAT SHE NEEDED US AT 6000 FT. FOR 15 MI WE COMPLIED. IN AND OUT OF CLOUD BASES AT 6000 FT, BROKEN LAYER ABOVE, HDG 170 DEGS FOR DOWNWIND TO BASE LEG SET UP (VECTORED). NEARING PHL ARPT I INITIATED A CALL FOR REQUEST FOR LOWER. RADIO COMS WERE TIGHT AND BUSY. AT END OF XMISSION FOR LOWER, I HEARD A BROKEN COM FOR A HDG TO 090 DEGS -- NO ACFT CALL SIGN. NO ONE ACKNOWLEDGED ATC'S COMMAND. THE DIRECTIVE WAS NOT ISSUED AGAIN. I QUESTIONED APCH TWICE AS TO WHO THE HEADING WAS FOR WITH NO REPLY. CAPT (PF) STAYED ON 170 DEG HDG. CTLR CAME BACK UP, SAYING SHE WAS ON LAND LINE. I QUESTIONED AGAIN (THIRD XMISSION ON SAME QUESTION). SHE DIRECTED US TO TURN HARD 070 DEGS -- VFR TARGET HAD 'POPPED' UP ABOVE US AT 6500 FT. TCASII IDENTED TARGET AS A TA (AMBER), THEN TURNED TO RA (RED) 'DSND, DSND, DSND' JUST AS THE CAPT CLICKED OFF AUTOPLT, BANKED 40 DEGS L AND BEGAN DSCNT AT 4000 FPM. I INFORMED APCH THAT WE WERE DSNDING OUT OF 6000 FT ON AN RA. CAPT STOPPED DSCNT AT 5300 FT AFTER RA CEASED. I INFORMED CTLR THAT WE WERE AT 5300 FT. SHE REPLIED SHE NEEDED US AT 6000 FT. WE COMPLIED, CLBED AND WAS HANDED OFF TO FINAL CTLR FOR A NON EVENTFUL LNDG AT PHL. OUR BEST ESTIMATION IS THAT THE TFC CAUSING THE RA WAS 300 FT ABOVE AT ITS LOWEST ALT, AND AS CLOSE AS 400-500 FT HORIZLY 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.