Narrative:

Just a few mins prior to our altitude deviation, we had received a TCASII climb RA which was valid and this contributed to what happened. The first officer was flying the aircraft only 10 months as copilot, and we were cleared to 3000 ft on a downwind. I was talking to approach and trying to locate the airport and keep a traffic watch. I checked that the first officer was leveling at 3000 ft and looked back out. For some reason the first officer thought we were cleared for the visual and for some unexplained reason 1000 ft was set in the altitude alert window. I know that I didn't set it and he said that he hadn't. As we were turning toward the airport, I sensed we were descending and turned my attention back in the cockpit and saw we were descending. I told him to stop the descent at 2500 ft, and told approach we had the airport. Approach had no comment except to clear us for the approach. They did ask me to call the supervisor on the ground but the only thing he wanted was information on our TCASII RA. I believe the main factor in this was that both of us had a break in concentration due to the TCASII RA as it would have been a very near miss if not for TCASII. Another factor which may have contributed was the relative inexperience of the first officer, about 150-200 hours in 10 months. I let my attention focus more on looking for traffic and the airport and I should have been paying more attention to the flying.

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Original NASA ASRS Text

Title: AN MLG ACR ACFT HAD A TCASII RA NEAR THE TFC PATTERN, THEN THE COPLT HAD AN ALTDEV IN THE TFC PATTERN.

Narrative: JUST A FEW MINS PRIOR TO OUR ALTDEV, WE HAD RECEIVED A TCASII CLB RA WHICH WAS VALID AND THIS CONTRIBUTED TO WHAT HAPPENED. THE FO WAS FLYING THE ACFT ONLY 10 MONTHS AS COPLT, AND WE WERE CLRED TO 3000 FT ON A DOWNWIND. I WAS TALKING TO APCH AND TRYING TO LOCATE THE ARPT AND KEEP A TFC WATCH. I CHKED THAT THE FO WAS LEVELING AT 3000 FT AND LOOKED BACK OUT. FOR SOME REASON THE FO THOUGHT WE WERE CLRED FOR THE VISUAL AND FOR SOME UNEXPLAINED REASON 1000 FT WAS SET IN THE ALT ALERT WINDOW. I KNOW THAT I DIDN'T SET IT AND HE SAID THAT HE HADN'T. AS WE WERE TURNING TOWARD THE ARPT, I SENSED WE WERE DSNDING AND TURNED MY ATTN BACK IN THE COCKPIT AND SAW WE WERE DSNDING. I TOLD HIM TO STOP THE DSCNT AT 2500 FT, AND TOLD APCH WE HAD THE ARPT. APCH HAD NO COMMENT EXCEPT TO CLR US FOR THE APCH. THEY DID ASK ME TO CALL THE SUPVR ON THE GND BUT THE ONLY THING HE WANTED WAS INFO ON OUR TCASII RA. I BELIEVE THE MAIN FACTOR IN THIS WAS THAT BOTH OF US HAD A BREAK IN CONCENTRATION DUE TO THE TCASII RA AS IT WOULD HAVE BEEN A VERY NEAR MISS IF NOT FOR TCASII. ANOTHER FACTOR WHICH MAY HAVE CONTRIBUTED WAS THE RELATIVE INEXPERIENCE OF THE FO, ABOUT 150-200 HRS IN 10 MONTHS. I LET MY ATTN FOCUS MORE ON LOOKING FOR TFC AND THE ARPT AND I SHOULD HAVE BEEN PAYING MORE ATTN TO THE FLYING.

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.