Narrative:

While being vectored to final approach for runway 33L at bwi, received TCASII RA 'descend.' departed 3000 ft assigned altitude for 2500 ft when controller (who was unable to get in a word on frequency due to heavy traffic) called out traffic to us at '10-11 O'clock less than a mi descend to 2000 ft.' we were already in the descent as the controller spoke and 'clear of conflict' advisory came from the TCASII as we passed 2500 ft on the descent. Without TCASII our traffic conflict would have been closer but approach control's call would have been in time to prevent a collision.

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Original NASA ASRS Text

Title: TCASII CAUSES MLG TO DSND TO AVOID CONFLICTING TFC.

Narrative: WHILE BEING VECTORED TO FINAL APCH FOR RWY 33L AT BWI, RECEIVED TCASII RA 'DSND.' DEPARTED 3000 FT ASSIGNED ALT FOR 2500 FT WHEN CTLR (WHO WAS UNABLE TO GET IN A WORD ON FREQ DUE TO HVY TFC) CALLED OUT TFC TO US AT '10-11 O'CLOCK LESS THAN A MI DSND TO 2000 FT.' WE WERE ALREADY IN THE DSCNT AS THE CTLR SPOKE AND 'CLR OF CONFLICT' ADVISORY CAME FROM THE TCASII AS WE PASSED 2500 FT ON THE DSCNT. WITHOUT TCASII OUR TFC CONFLICT WOULD HAVE BEEN CLOSER BUT APCH CTL'S CALL WOULD HAVE BEEN IN TIME TO PREVENT A COLLISION.

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.