Narrative:

While descending on the phlbo STAR into ewr; passing through 8;300 for 8;000; we received a TCAS RA to 'descend' and 'monitor vertical speed.' shortly after that ATC called traffic at 12 o'clock and 1.5 miles at 8;200 ft. I replied that was the same altitude we were passing through and that we were responding to a TCAS RA. ATC cleared us to continue descent to 6;000. We then visually acquired a cessna approaching us head-on and co-altitude. I pointed out the traffic to the first officer and told him to increase the descent rate. The aircraft passed by just slightly left and above us (approximately 200 - 300 ft of separation. ATC subsequently said the aircraft was at 8;500 ft; but may have descended to avoid a cloud. However; from our vantage point we could see only scattered wisps of clouds above; but a solid deck below at about 5;500 ft. I advised that it was way; way too close for comfort. The rest of the flight was uneventful.the cessna may not have been at the proper altitude; but would have still been a factor for our descent even if he had been at 8;500 ft. No traffic advisories were given until the RA was received and being responded to. I have no idea why a VFR aircraft was flying directly against the arrival flow into a major airport at an altitude through which all inbound aircraft must descend.just glad TCAS was working. It has become more common to see this equipment on MEL; so I am extremely glad it was functioning properly. The results of this incident would have been decidedly different without it. Also glad we were able to visually acquire the target in sufficient time; albeit with the help of the TCAS.

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Original NASA ASRS Text

Title: An EMB-145 descending via the PHLBO STAR suffered an NMAC with opposite direction VFR traffic.

Narrative: While descending on the PHLBO STAR into EWR; passing through 8;300 for 8;000; we received a TCAS RA to 'descend' and 'monitor vertical speed.' Shortly after that ATC called traffic at 12 o'clock and 1.5 miles at 8;200 FT. I replied that was the same altitude we were passing through and that we were responding to a TCAS RA. ATC cleared us to continue descent to 6;000. We then visually acquired a Cessna approaching us head-on and co-altitude. I pointed out the traffic to the First Officer and told him to increase the descent rate. The aircraft passed by just slightly left and above us (approximately 200 - 300 FT of separation. ATC subsequently said the aircraft was at 8;500 FT; but may have descended to avoid a cloud. However; from our vantage point we could see only scattered wisps of clouds above; but a solid deck below at about 5;500 FT. I advised that it was way; way too close for comfort. The rest of the flight was uneventful.The Cessna may not have been at the proper altitude; but would have still been a factor for our descent even if he had been at 8;500 FT. No traffic advisories were given until the RA was received and being responded to. I have no idea why a VFR aircraft was flying directly against the arrival flow into a major airport at an altitude through which all inbound aircraft must descend.Just glad TCAS was working. It has become more common to see this equipment on MEL; so I am extremely glad it was functioning properly. The results of this incident would have been decidedly different without it. Also glad we were able to visually acquire the target in sufficient time; albeit with the help of the TCAS.

Data retrieved from NASA's ASRS site as of July 2013 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.