Narrative:

[I] noticed TCAS traffic at 9-10 o'clock position at 5 miles co-altitude. No word from approach control. [Traffic was at a] constant bearing decreasing range to a near miss. Received TCAS RA at approximately 1.5 miles and complied with command to descend. We were level at 4;000 ft at approach fix dadey on approach to 19L iad. We descended to 3;500 ft during evasive reaction; threat aircraft descended as well. [We] missed aircraft by 500 ft horizontal and approximately 50 ft vertical. It appeared threat aircraft was trying to avoid our aircraft. After miss; contacted approach control to notify [them] we had descended to 3;500 ft for TCAS RA. Approach cleared us to continue descend to 3;000; no further action; normal landing.

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Original NASA ASRS Text

Title: CRJ200 Captain at 4;000 FT reports TCAS RA at fix DADEY during approach to Runway 19L at IAD; which resulted in evasive action taken by the Reporter.

Narrative: [I] noticed TCAS traffic at 9-10 o'clock position at 5 miles co-altitude. No word from Approach Control. [Traffic was at a] constant bearing decreasing range to a near miss. Received TCAS RA at approximately 1.5 miles and complied with command to descend. We were level at 4;000 FT at approach fix DADEY on approach to 19L IAD. We descended to 3;500 FT during evasive reaction; threat aircraft descended as well. [We] missed aircraft by 500 FT horizontal and approximately 50 FT vertical. It appeared threat aircraft was trying to avoid our aircraft. After miss; contacted Approach Control to notify [them] we had descended to 3;500 FT for TCAS RA. Approach cleared us to continue descend to 3;000; no further action; normal landing.

Data retrieved from NASA's ASRS site as of April 2012 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.