Narrative:

The deviation occurred at the end of the total scenario that lasted approximately 20-30 seconds. First, I was in an idle descent, LNAV, level change and autoplt on to an altitude of 15000 ft MSL. As I was descending through approximately 16000-16300 ft MSL, I had a 'traffic, traffic,' TCASII and I then went to a vertical speed of about 1000-1500 FPM to keep from getting an RA but at about 15300 ft MSL I received a 'climb, climb, climb,' TCASII RA. I then disconnected the autoplt and followed the TCASII RA to approximately 15800-16200 ft when TCASII said 'monitor vertical speed.' I then stopped my ascent and started back down to 15000 ft MSL assigned because I was at approximately 15800-16200 ft. Second, the RA was complied with adherence to SOP and completed when TCASII said 'clear of conflict.' I was now descending through approximately 16200 ft to 15000 ft with the autoplt off. As I am approaching 15000 ft for the second time, the TCASII says 'traffic, traffic,' again with the same target to my right which is north of my position. Because it was VMC, I felt a big desire to acquire the traffic visually and I did see the brasilia aircraft. I then stated to the captain 'I have the aircraft in sight, no factor.' this all happened at once and I was visually fixated on the aircraft for a moment of time and descended through my altitude. As we caught our own deviation, I immediately went back to 15000 ft. In closing, this event took approximately 20-30 seconds from beginning to end. The human factors workload tasking was very high and intense with another aircraft in the area. Acquiring the aircraft visually was a relief and an important task at the particular moment in time. The situation was too dynamic and short to come up with a quick solution to this situation.

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Original NASA ASRS Text

Title: B737-300 DSCNT TO OCCUPIED ALT. TCASII RA SENDS HIM INTO EVASIVE ACTION CLB DSCNT. ALT OVERSHOOT IN DSCNT.

Narrative: THE DEV OCCURRED AT THE END OF THE TOTAL SCENARIO THAT LASTED APPROX 20-30 SECONDS. FIRST, I WAS IN AN IDLE DSCNT, LNAV, LEVEL CHANGE AND AUTOPLT ON TO AN ALT OF 15000 FT MSL. AS I WAS DSNDING THROUGH APPROX 16000-16300 FT MSL, I HAD A 'TFC, TFC,' TCASII AND I THEN WENT TO A VERT SPD OF ABOUT 1000-1500 FPM TO KEEP FROM GETTING AN RA BUT AT ABOUT 15300 FT MSL I RECEIVED A 'CLB, CLB, CLB,' TCASII RA. I THEN DISCONNECTED THE AUTOPLT AND FOLLOWED THE TCASII RA TO APPROX 15800-16200 FT WHEN TCASII SAID 'MONITOR VERT SPD.' I THEN STOPPED MY ASCENT AND STARTED BACK DOWN TO 15000 FT MSL ASSIGNED BECAUSE I WAS AT APPROX 15800-16200 FT. SECOND, THE RA WAS COMPLIED WITH ADHERENCE TO SOP AND COMPLETED WHEN TCASII SAID 'CLR OF CONFLICT.' I WAS NOW DSNDING THROUGH APPROX 16200 FT TO 15000 FT WITH THE AUTOPLT OFF. AS I AM APCHING 15000 FT FOR THE SECOND TIME, THE TCASII SAYS 'TFC, TFC,' AGAIN WITH THE SAME TARGET TO MY R WHICH IS N OF MY POS. BECAUSE IT WAS VMC, I FELT A BIG DESIRE TO ACQUIRE THE TFC VISUALLY AND I DID SEE THE BRASILIA ACFT. I THEN STATED TO THE CAPT 'I HAVE THE ACFT IN SIGHT, NO FACTOR.' THIS ALL HAPPENED AT ONCE AND I WAS VISUALLY FIXATED ON THE ACFT FOR A MOMENT OF TIME AND DSNDED THROUGH MY ALT. AS WE CAUGHT OUR OWN DEV, I IMMEDIATELY WENT BACK TO 15000 FT. IN CLOSING, THIS EVENT TOOK APPROX 20-30 SECONDS FROM BEGINNING TO END. THE HUMAN FACTORS WORKLOAD TASKING WAS VERY HIGH AND INTENSE WITH ANOTHER ACFT IN THE AREA. ACQUIRING THE ACFT VISUALLY WAS A RELIEF AND AN IMPORTANT TASK AT THE PARTICULAR MOMENT IN TIME. THE SIT WAS TOO DYNAMIC AND SHORT TO COME UP WITH A QUICK SOLUTION TO THIS SIT.

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.