Narrative:

During communication with bwi approach, traffic reported at 1 O'clock, unknown altitude. TCASII alert issued to descend. Aircraft descended to 11500 ft. At that altitude, traffic was seen directly overhead. Approach control was notified and acted as if unaware of traffic. Without comment, he handed us off to next controller. Better handling and awareness by ATC may have averted what could have been a disaster. Callback conversation with reporter revealed the following information: the reporter flies the MD80. There was good visibility at the time of this incident. The reporter believes that his TCASII was operating properly, that this was no false alarm. 'This would have been really close if not a hit' except for the TCASII warning. He is upset with the rather cavalier attitude taken by the ARTCC controller who offered no explanation or apology, just a fast handoff to the next sector. The reporter does not remember what type aircraft was overhead, but it was not an air carrier. The 500 ft altitude differential was an estimate. Initially the TCASII showed the intruder to be at the same level and the reporter descended 500 ft. Hence the estimate. The reporter believes that the intruder did not have altitude reporting capability.

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Original NASA ASRS Text

Title: NMAC BTWN AN ACR AND AN UNKNOWN ACFT.

Narrative: DURING COM WITH BWI APCH, TFC RPTED AT 1 O'CLOCK, UNKNOWN ALT. TCASII ALERT ISSUED TO DSND. ACFT DSNDED TO 11500 FT. AT THAT ALT, TFC WAS SEEN DIRECTLY OVERHEAD. APCH CTL WAS NOTIFIED AND ACTED AS IF UNAWARE OF TFC. WITHOUT COMMENT, HE HANDED US OFF TO NEXT CTLR. BETTER HANDLING AND AWARENESS BY ATC MAY HAVE AVERTED WHAT COULD HAVE BEEN A DISASTER. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR FLIES THE MD80. THERE WAS GOOD VISIBILITY AT THE TIME OF THIS INCIDENT. THE RPTR BELIEVES THAT HIS TCASII WAS OPERATING PROPERLY, THAT THIS WAS NO FALSE ALARM. 'THIS WOULD HAVE BEEN REALLY CLOSE IF NOT A HIT' EXCEPT FOR THE TCASII WARNING. HE IS UPSET WITH THE RATHER CAVALIER ATTITUDE TAKEN BY THE ARTCC CTLR WHO OFFERED NO EXPLANATION OR APOLOGY, JUST A FAST HDOF TO THE NEXT SECTOR. THE RPTR DOES NOT REMEMBER WHAT TYPE ACFT WAS OVERHEAD, BUT IT WAS NOT AN ACR. THE 500 FT ALT DIFFERENTIAL WAS AN ESTIMATE. INITIALLY THE TCASII SHOWED THE INTRUDER TO BE AT THE SAME LEVEL AND THE RPTR DSNDED 500 FT. HENCE THE ESTIMATE. THE RPTR BELIEVES THAT THE INTRUDER DID NOT HAVE ALT RPTING CAPABILITY.

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.