Narrative:

On a downwind; I slowed and called for flaps 5 in anticipation of an early turn to final. TCAS showed traffic on final near our 10 o'clock position and we were still descending through 4;000 ft. I anticipated that a turn behind this traffic would result in a smooth approach to a stabilized final; as the traffic moved to 9 o'clock; approach called out our sequence traffic at 10 to 11 o'clock and south of macdill. It was a very good and very accurate call. I looked to that position both outside and on TCAS. Not seeing any traffic at the callout location; we continued on downwind a few more seconds while I told my first officer I had the guy passing our 9 o'clock. At this point; I placed too much priority on my energy state and started a slow turn to base while ATC gave us one more callout for our sequence. I rolled out; again looked in that direction; and again referenced TCAS. We still did not see any traffic in that position. It is here that I assumed the position call was in error and started to concentrate on the approach. While on base; approach asked us to confirm we had the B757 traffic on the nose. I rolled out of the turn and saw the B757 on final and less than four miles ahead. ATC then cancelled our approach clearance and provided vectors for another approach. This event was caused by a series of errors on my part. First; my early configuration added another task to our workload at an inappropriate time. I put too high a priority on approach energy management before I made certain of our sequence. Second; I allowed myself to question ATC's position report based on two very fallible sources: 1) visual acuity in a hazy environment and 2) TCAS. As long as the position reports were questionable; I should have remained on my heading. In the future; I will keep tasks in order. I will verify our sequence before configuring and adding responsibilities at inappropriate times.

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Original NASA ASRS Text

Title: The Tower Controller issued a go around to a B737-300 flight crew who lost separation with the aircraft they were following.

Narrative: On a downwind; I slowed and called for flaps 5 in anticipation of an early turn to final. TCAS showed traffic on final near our 10 o'clock position and we were still descending through 4;000 FT. I anticipated that a turn behind this traffic would result in a smooth approach to a stabilized final; as the traffic moved to 9 o'clock; Approach called out our sequence traffic at 10 to 11 o'clock and south of MacDill. It was a very good and very accurate call. I looked to that position both outside and on TCAS. Not seeing any traffic at the callout location; we continued on downwind a few more seconds while I told my First Officer I had the guy passing our 9 o'clock. At this point; I placed too much priority on my energy state and started a slow turn to base while ATC gave us one more callout for our sequence. I rolled out; again looked in that direction; and again referenced TCAS. We still did not see any traffic in that position. It is here that I assumed the position call was in error and started to concentrate on the approach. While on base; Approach asked us to confirm we had the B757 traffic on the nose. I rolled out of the turn and saw the B757 on final and less than four miles ahead. ATC then cancelled our approach clearance and provided vectors for another approach. This event was caused by a series of errors on my part. First; my early configuration added another task to our workload at an inappropriate time. I put too high a priority on approach energy management before I made certain of our sequence. Second; I allowed myself to question ATC's position report based on two very fallible sources: 1) visual acuity in a hazy environment and 2) TCAS. As long as the position reports were questionable; I should have remained on my heading. In the future; I will keep tasks in order. I will verify our sequence before configuring and adding responsibilities at inappropriate times.

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.