Narrative:

We were under IFR control proceeding direct to bwi, level at 10000 ft MSL. Bwi approach informed us of traffic, 12 O'clock, opposite direction climbing VFR 'through' 9500 ft MSL. All 3 of us understood the controller to say climbing 'to' 9500 ft MSL. At approximately 6 mi, the VFR traffic appeared on our TCASII screen 600 ft below us and climbing. When he reached about 4 mi, 400 ft below and still climbing, we heard the TCASII announce 'traffic, traffic.' at less than 2 mi, we still had not visually acquired the traffic which was now co-altitude. That was when the TCASII commanded, 'descend, descend.' I disconnected the autoplt and pushed forward and then looked up to see the small twin engine plane directly in front of me at about 1 - 1 1/2 mi. I looked down at the TCASII as I continued my descent and saw that the plane was about 100 ft above me. As the plane passed overhead, we had about 600 ft of vertical separation and no lateral separation. Just then, the controller warned us to maintain 10000 ft and the TCASII RA commanded us to 'monitor vertical speed.' our descent bottomed out at approximately 9200 ft MSL and I climbed immediately back to 10000 ft.' we advised bwi approach that we were responding to an RA. Upon landing at dca, there were no comments from the 4 flight attendants or 115+ passenger that indicated they noticed the incident. The captain called a supervisor at bwi approach who said the pilot of the other aircraft had us in sight and was cleared 'through' 9500 ft (vice 'to' 9500 ft). I believe that the evasive maneuver that I performed in response to the TCASII RA prevented a near miss that would have been within 150 ft of the other aircraft. I do not believe that the pilot of the other aircraft had us in sight, and I do not think that the approach controller should have allowed us to get that close anyway.

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Original NASA ASRS Text

Title: B727 AND A LIGHT TWIN HAVE A CONFLICT RESOLVED BY TCASII RA.

Narrative: WE WERE UNDER IFR CTL PROCEEDING DIRECT TO BWI, LEVEL AT 10000 FT MSL. BWI APCH INFORMED US OF TFC, 12 O'CLOCK, OPPOSITE DIRECTION CLBING VFR 'THROUGH' 9500 FT MSL. ALL 3 OF US UNDERSTOOD THE CTLR TO SAY CLBING 'TO' 9500 FT MSL. AT APPROX 6 MI, THE VFR TFC APPEARED ON OUR TCASII SCREEN 600 FT BELOW US AND CLBING. WHEN HE REACHED ABOUT 4 MI, 400 FT BELOW AND STILL CLBING, WE HEARD THE TCASII ANNOUNCE 'TFC, TFC.' AT LESS THAN 2 MI, WE STILL HAD NOT VISUALLY ACQUIRED THE TFC WHICH WAS NOW CO-ALT. THAT WAS WHEN THE TCASII COMMANDED, 'DSND, DSND.' I DISCONNECTED THE AUTOPLT AND PUSHED FORWARD AND THEN LOOKED UP TO SEE THE SMALL TWIN ENG PLANE DIRECTLY IN FRONT OF ME AT ABOUT 1 - 1 1/2 MI. I LOOKED DOWN AT THE TCASII AS I CONTINUED MY DSCNT AND SAW THAT THE PLANE WAS ABOUT 100 FT ABOVE ME. AS THE PLANE PASSED OVERHEAD, WE HAD ABOUT 600 FT OF VERT SEPARATION AND NO LATERAL SEPARATION. JUST THEN, THE CTLR WARNED US TO MAINTAIN 10000 FT AND THE TCASII RA COMMANDED US TO 'MONITOR VERT SPD.' OUR DSCNT BOTTOMED OUT AT APPROX 9200 FT MSL AND I CLBED IMMEDIATELY BACK TO 10000 FT.' WE ADVISED BWI APCH THAT WE WERE RESPONDING TO AN RA. UPON LNDG AT DCA, THERE WERE NO COMMENTS FROM THE 4 FLT ATTENDANTS OR 115+ PAX THAT INDICATED THEY NOTICED THE INCIDENT. THE CAPT CALLED A SUPVR AT BWI APCH WHO SAID THE PLT OF THE OTHER ACFT HAD US IN SIGHT AND WAS CLRED 'THROUGH' 9500 FT (VICE 'TO' 9500 FT). I BELIEVE THAT THE EVASIVE MANEUVER THAT I PERFORMED IN RESPONSE TO THE TCASII RA PREVENTED A NEAR MISS THAT WOULD HAVE BEEN WITHIN 150 FT OF THE OTHER ACFT. I DO NOT BELIEVE THAT THE PLT OF THE OTHER ACFT HAD US IN SIGHT, AND I DO NOT THINK THAT THE APCH CTLR SHOULD HAVE ALLOWED US TO GET THAT CLOSE ANYWAY.

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.