Narrative:

It was a VFR day. We were on the irons arrival into dca at 8000 ft. We received a TA on TCASII. We spotted the traffic at 1 O'clock. TCASII revealed the traffic was at 8400 ft. The traffic was to pass over our aircraft. Then a RA appeared on TCASII to descend of at least 1500 FPM. As the PF I followed the RA. At 7600 ft the TCASII revealed we were clear of traffic, then we climbed back to 8000 ft. When we notified ATC of our traffic and subsequent deviation they issued a TA for the first time. There was no further incident on our arrival to dca.

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Original NASA ASRS Text

Title: PLTDEV FROM TCASII RA EVASIVE ACTION FROM UNKNOWN ACFT.

Narrative: IT WAS A VFR DAY. WE WERE ON THE IRONS ARR INTO DCA AT 8000 FT. WE RECEIVED A TA ON TCASII. WE SPOTTED THE TFC AT 1 O'CLOCK. TCASII REVEALED THE TFC WAS AT 8400 FT. THE TFC WAS TO PASS OVER OUR ACFT. THEN A RA APPEARED ON TCASII TO DSND OF AT LEAST 1500 FPM. AS THE PF I FOLLOWED THE RA. AT 7600 FT THE TCASII REVEALED WE WERE CLR OF TFC, THEN WE CLBED BACK TO 8000 FT. WHEN WE NOTIFIED ATC OF OUR TFC AND SUBSEQUENT DEV THEY ISSUED A TA FOR THE FIRST TIME. THERE WAS NO FURTHER INCIDENT ON OUR ARR TO DCA.

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.