Narrative:

We were cleared for the ILS Z approach to runway 10; as we passed the paz VOR outbound we began our descent from the initial approach altitude of 18;000 ft to 15;000 ft. At approximately 4 miles from the VOR; on the outbound leg; traffic popped up and was observed on TCAS by the first officer. We weren't able to get a visual since the aircraft was almost directly below us. We were descending at approximately 800 to 1;000 ft per minute. I started to level our aircraft at approximately 15;500 ft. At this point the other aircraft started a rapid climb in our direction. Within a couple of seconds we got an right/a from our TCAS commanding a climb. I immediately disconnected the auto pilot and auto throttles and pitched up so as to keep the aircraft in the green on the vertical speed indicator. There were 2 green dots at the top of the indicator; the rest was red. I used max power and had to peg the vsi (6;000 FPM) to out climb the threat. The aircraft was still converging at [such] a rate that we all were anticipating contact. The aircraft came within 200 ft of our underbelly. Once we determined the aircraft was no longer a threat I leveled our aircraft at approximately 19;500 ft; performed a descending 360 degree turn to get back to the initial approach altitude; and then completed the ILS approach. We never saw the other aircraft.

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Original NASA ASRS Text

Title: Flight crew arriving SLLP and cleared for the ILS Z Runway 10 approach reports TCAS RA and NMAC with aircraft climbing under them on the PAZ 305 radial. A maximum rate climb and maneuvering eventually results in a clear of conflict TCAS announcement.

Narrative: We were cleared for the ILS Z approach to Runway 10; as we passed the PAZ VOR outbound we began our descent from the initial approach altitude of 18;000 FT to 15;000 FT. At approximately 4 miles from the VOR; on the outbound leg; traffic popped up and was observed on TCAS by the First Officer. We weren't able to get a visual since the aircraft was almost directly below us. We were descending at approximately 800 to 1;000 FT per minute. I started to level our aircraft at approximately 15;500 FT. At this point the other aircraft started a rapid climb in our direction. Within a couple of seconds we got an R/A from our TCAS commanding a climb. I immediately disconnected the auto pilot and auto throttles and pitched up so as to keep the aircraft in the green on the vertical speed indicator. There were 2 green dots at the top of the indicator; the rest was red. I used max power and had to peg the VSI (6;000 FPM) to out climb the threat. The aircraft was still converging at [such] a rate that we all were anticipating contact. The aircraft came within 200 FT of our underbelly. Once we determined the aircraft was no longer a threat I leveled our aircraft at approximately 19;500 FT; performed a descending 360 degree turn to get back to the initial approach altitude; and then completed the ILS approach. We never saw the other aircraft.

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.