Narrative:

The following describes the events leading up to the RA. We were on the sayge 6 arrival to centennial airport; when at sayge intersection (at FL190/250 KTS; as cleared by ZDV); we were given a heading of 180 degrees and told to descend to 11000 ft MSL. After leveloff at 11000 ft MSL we were given a heading of 230 degrees and a descent to 9000 ft MSL. After a leveloff at 9000 ft MSL we were assigned a heading of 270 degrees and a descent to 8000 ft MSL. Shortly after a rollout on the 270 degree heading and the descent to 8000 ft MSL; I received a verbal 'traffic' from the TCAS and an immediate 'climb; climb.' I immediately and simultaneously; disconnected the autoplt and pitched the aircraft up to match the TCAS climb indications. We never saw the other aircraft but followed it on the TCAS display go underneath our aircraft. We reported to denver approach control; who had been vectoring us from sayge intersection; that we had received an RA and was now returning to our assigned altitude of 8000 ft MSL. The controller said she did not see the conflict traffic. We continued to centennial airport for a visual approach to runway 17L. I have no idea why the controller never saw the traffic and why we had only a limited time to react to the traffic. Until the last moment; we had no indication of the traffic that effected the RA.

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Original NASA ASRS Text

Title: A G200 REPORTS AN RA FROM UNREPORTED TFC ON THE APA SAYGE ARR DESCENDING TO 8000 FT. ATC DID NOT SEE THE TFC.

Narrative: THE FOLLOWING DESCRIBES THE EVENTS LEADING UP TO THE RA. WE WERE ON THE SAYGE 6 ARR TO CENTENNIAL ARPT; WHEN AT SAYGE INTXN (AT FL190/250 KTS; AS CLRED BY ZDV); WE WERE GIVEN A HDG OF 180 DEGS AND TOLD TO DSND TO 11000 FT MSL. AFTER LEVELOFF AT 11000 FT MSL WE WERE GIVEN A HDG OF 230 DEGS AND A DSCNT TO 9000 FT MSL. AFTER A LEVELOFF AT 9000 FT MSL WE WERE ASSIGNED A HDG OF 270 DEGS AND A DSCNT TO 8000 FT MSL. SHORTLY AFTER A ROLLOUT ON THE 270 DEG HDG AND THE DSCNT TO 8000 FT MSL; I RECEIVED A VERBAL 'TFC' FROM THE TCAS AND AN IMMEDIATE 'CLB; CLB.' I IMMEDIATELY AND SIMULTANEOUSLY; DISCONNECTED THE AUTOPLT AND PITCHED THE ACFT UP TO MATCH THE TCAS CLB INDICATIONS. WE NEVER SAW THE OTHER ACFT BUT FOLLOWED IT ON THE TCAS DISPLAY GO UNDERNEATH OUR ACFT. WE RPTED TO DENVER APCH CTL; WHO HAD BEEN VECTORING US FROM SAYGE INTXN; THAT WE HAD RECEIVED AN RA AND WAS NOW RETURNING TO OUR ASSIGNED ALT OF 8000 FT MSL. THE CTLR SAID SHE DID NOT SEE THE CONFLICT TFC. WE CONTINUED TO CENTENNIAL ARPT FOR A VISUAL APCH TO RWY 17L. I HAVE NO IDEA WHY THE CTLR NEVER SAW THE TFC AND WHY WE HAD ONLY A LIMITED TIME TO REACT TO THE TFC. UNTIL THE LAST MOMENT; WE HAD NO INDICATION OF THE TFC THAT EFFECTED THE RA.

Data retrieved from NASA's ASRS site as of January 2009 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.