Narrative:

Please allow me to be as objective as I can about my version of a TCAS event in den. However; this version is basically a subjective version on my best memory of this RA event. The flight was just establishing on the localizer; turning just outside (approximately 0.2 DME) of leets on den 16L (i.e.; localizer capture) from a converging heading of 220 degrees (50-degree intercept). The flight was very dynamic; as we were level at 7;000 ft MSL and cleared for the approach; when almost instantaneously at glide slope capture the threat traffic was on den 16R inside jetsn triggering our RA. (They were 100 ft below and ahead of us to the right; i.e.; -01 at our 12 moving to 1 o'clock position. We were hard banking on capture to localizer). As the pilot flying; I maneuvered in response to the RA as usual; and the pilot not flying radioed an advisory notifying ATC of our deviating below glide slope in response to a descend RA. I do not believe ATC responded; and the threat aircraft did not respond in kind (perhaps they were in TA mode).the pilot flying followed the planned lateral flight path (descend arrow); with immediate disengagement of the autopilot and auto throttle systems to meet the requirements of TCAS ii maneuvering; flying the aircraft symbol out of the red-outlined area on the ADI out of the red band; except the excursion from the glide slope was increasingly directing us to drive the aircraft into the ground at low altitude. I cannot recall; but my memory recounts we were passing 600 ft AGL by increasing or maintaining the existing descending vertical separation developing by the threat aircraft; which was also descending below our altitude. The maneuvering was fast approaching a 1 1/2 dots deviation below the glide slope indication in VMC (runway was in sight); and under the circumstances; I decided it most appropriate to switch the TA only mode (to avoid a GPWS warning) and climb back to the glide slope indication; as the traffic conflict was resolved; meaning we had ascertained visual on the threat traffic on 16R just before switching TCAS to TA mode (with no other proximate traffic; TA; or RA). We continued with the visual approach to the runway on glide path without any further issues. The possibility of a TCAS RA was advised on the 10-7A page 'arrivals: 1. Due to the fact that 16R and 16L are separated by only 2;500 ft; there is an increased possibility of TCAS tas or ras within 10 NM from the FAF to the FAF for 16L and 16R; especially during periods of high traffic density.' however; no advisory or instruction was dictated telling me to switch the TCAS to a TA only mode for this approach (such as on visual approaches to sfo for 28L/right). And I thought all ras are inhibited below 900 ft radio altitude during descents; and I am pretty sure we were below 900 ft AGL when we continued to receive the red-outlined area on the ADI out of the red band. Our flight received the threat traffic as 'proximate traffic' on TCAS; but we never received a TA before receiving the RA.

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Original NASA ASRS Text

Title: An air carrier Captain took evasive action to a TCAS RA while he captured the DEN 16L localizer. The descend RA command was followed below 600 FT AGL where TCAS TA was selected and the glide slope rejoined.

Narrative: Please allow me to be as objective as I can about my version of a TCAS event in DEN. However; this version is basically a subjective version on my best memory of this RA event. The flight was just establishing on the LOC; turning just outside (approximately 0.2 DME) of LEETS on DEN 16L (i.e.; localizer capture) from a converging heading of 220 degrees (50-degree intercept). The flight was very dynamic; as we were level at 7;000 FT MSL and cleared for the approach; when almost instantaneously at glide slope capture the threat traffic was on DEN 16R inside JETSN triggering our RA. (They were 100 FT below and ahead of us to the right; i.e.; -01 at our 12 moving to 1 o'clock position. We were hard banking on capture to Localizer). As the pilot flying; I maneuvered in response to the RA as usual; and the pilot not flying radioed an advisory notifying ATC of our deviating below glide slope in response to a descend RA. I do not believe ATC responded; and the threat aircraft did not respond in kind (perhaps they were in TA mode).The pilot flying followed the planned lateral flight path (descend arrow); with immediate disengagement of the autopilot and auto throttle systems to meet the requirements of TCAS II maneuvering; flying the aircraft symbol out of the red-outlined area on the ADI out of the red band; except the excursion from the glide slope was increasingly directing us to drive the aircraft into the ground at low altitude. I cannot recall; but my memory recounts we were passing 600 FT AGL by increasing or maintaining the existing descending vertical separation developing by the threat aircraft; which was also descending below our altitude. The maneuvering was fast approaching a 1 1/2 dots deviation below the glide slope indication in VMC (runway was in sight); and under the circumstances; I decided it most appropriate to switch the TA ONLY mode (to avoid a GPWS warning) and climb back to the glide slope indication; as the traffic conflict was resolved; meaning we had ascertained visual on the threat traffic on 16R just before switching TCAS to TA mode (with no other proximate traffic; TA; or RA). We continued with the visual approach to the runway on glide path without any further issues. The possibility of a TCAS RA was advised on the 10-7A page 'ARRIVALS: 1. Due to the fact that 16R and 16L are separated by only 2;500 FT; there is an increased possibility of TCAS TAs or RAs within 10 NM from the FAF to the FAF for 16L and 16R; especially during periods of high traffic density.' However; no advisory or instruction was dictated telling me to switch the TCAS to a TA ONLY mode for this approach (such as on visual approaches to SFO for 28L/R). And I thought all RAs are inhibited below 900 FT radio altitude during descents; and I am pretty sure we were below 900 FT AGL when we continued to receive the red-outlined area on the ADI out of the red band. Our flight received the threat traffic as 'proximate traffic' on TCAS; but we never received a TA before receiving the RA.

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.