Narrative:

Departed on runway 9L at phl, called departure. Departure cleared us to 10000 ft with left turn to 360 degrees. During climb, turned us left to 270 degrees and climb to 12000 ft. Upon leaving 10000 ft, traffic was noticed on TCASII at 3 O'clock position, approximately 3-4 mi, 500 ft above us, descending and crossing our flight path. ATC was advised but initially did not see the traffic on his radar, but then did agree that he did see the traffic. Our climb was stopped at 10000 ft and TCASII announced an RA to descend. I immediately descended and made a left turn of approximately 30 degrees to avoid traffic. ATC was advised of our RA and our evasive action. The traffic proceeded to cross our flight path and evidently did not see us at all. ATC said the traffic was not talking to anyone and was proceeding VFR to a satellite airport.

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Original NASA ASRS Text

Title: POTENTIAL CONFLICT BTWN A DEP CLBING B757 AT 10000 FT AND UNKNOWN DSNDING VFR ACFT XING 5 NM NW OF PHL, PA.

Narrative: DEPARTED ON RWY 9L AT PHL, CALLED DEP. DEP CLRED US TO 10000 FT WITH L TURN TO 360 DEGS. DURING CLB, TURNED US L TO 270 DEGS AND CLB TO 12000 FT. UPON LEAVING 10000 FT, TFC WAS NOTICED ON TCASII AT 3 O'CLOCK POS, APPROX 3-4 MI, 500 FT ABOVE US, DSNDING AND XING OUR FLT PATH. ATC WAS ADVISED BUT INITIALLY DID NOT SEE THE TFC ON HIS RADAR, BUT THEN DID AGREE THAT HE DID SEE THE TFC. OUR CLB WAS STOPPED AT 10000 FT AND TCASII ANNOUNCED AN RA TO DSND. I IMMEDIATELY DSNDED AND MADE A L TURN OF APPROX 30 DEGS TO AVOID TFC. ATC WAS ADVISED OF OUR RA AND OUR EVASIVE ACTION. THE TFC PROCEEDED TO CROSS OUR FLT PATH AND EVIDENTLY DID NOT SEE US AT ALL. ATC SAID THE TFC WAS NOT TALKING TO ANYONE AND WAS PROCEEDING VFR TO A SATELLITE ARPT.

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.