Narrative:

The initial denver approach controller said to expect ILS 35R approach. Upon checking in with the final approach controller; he initially said vectors for ILS 35L. During our read back; he corrected himself and said it was for the ILS 35R. Again; with a heading of 320 assigned; he directed us to join the ILS 35L; when questioned; he corrected it back to the ILS 35R. After joining the ILS 35R approach; he cleared us to maintain 170kts to fronz (fronz is on the 35R ILS) and cleared us for the ILS 35L approach. At this time we told him he said ILS 35L again and he said that we were cleared for the ILS 35R approach and to contact tower on 133.3 (this frequency is for 35L normally; and we did have suspect that there was an error in this assignment.) while on the ILS 35R approach and waiting for a chance to check in with tower; we received a TA advisory followed by a 'monitor vertical speed' RA for traffic that appeared on the ILS 35L approach. Very shortly after this we received a RA climb command; and we immediately complied. As we were climbing; now well above the glide slope; we executed a missed approach. Our announcing the 'go around' to the tower controller was our first check in and we were told to 'standby'; then given and altitude and heading assignment which we complied with. There were other possible contributing factors that increased our workload and that of the controller's happening at this time. Our forecast was for VMC conditions at the airport. However; a proceeding aircraft cleared for the visual said he could not see the airport and needed the ILS. Realizing there was in fact a solid ovc; we briefed the CAT III ILS 35R in addition to our previously briefed CAT I briefing. We never got a chance to ask tower for current weather before executing the missed approach. During vectors for our second approach; we received the current ATIS again; still stating 10SM 120SCT. We were given a different tower frequency this time (normal freq for 35R). We experienced a solid 06 ovc on this approach. We reported this WX observation to ground control after landing. The following night with the same arrival time into denver; we flew a visual to 35R and were assigned the 133.3 frequency for tower. I do not know of any deviations on our part. Good weather info would have helped. Not sure what aircraft who caused the RA was doing or had been cleared for; but we were on the localizer for the ILS 35R.

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Original NASA ASRS Text

Title: Air carrier being vectored for approach to DEN experienced TCAS RA; describing confusion with regard to what runway ATC was assigning; 35L or 35R and weather factors as causal factors.

Narrative: The initial Denver approach controller said to expect ILS 35R approach. Upon checking in with the final Approach Controller; he initially said vectors for ILS 35L. During our read back; he corrected himself and said it was for the ILS 35R. Again; with a heading of 320 assigned; he directed us to join the ILS 35L; When questioned; he corrected it back to the ILS 35R. After joining the ILS 35R approach; he cleared us to maintain 170kts to FRONZ (FRONZ is on the 35R ILS) and cleared us for the ILS 35L approach. At this time we told him he said ILS 35L again and he said that we were cleared for the ILS 35R approach and to contact tower on 133.3 (This frequency is for 35L normally; and we did have suspect that there was an error in this assignment.) While on the ILS 35R approach and waiting for a chance to check in with tower; we received a TA advisory followed by a 'MONITOR VERTICAL SPEED' RA for traffic that appeared on the ILS 35L approach. Very shortly after this we received a RA climb command; and we immediately complied. As we were climbing; now well above the glide slope; we executed a missed approach. Our announcing the 'Go Around' to the tower controller was our first check in and we were told to 'standby'; then given and altitude and heading assignment which we complied with. There were other possible contributing factors that increased our workload and that of the controller's happening at this time. Our forecast was for VMC conditions at the airport. However; a proceeding aircraft cleared for the visual said he could not see the airport and needed the ILS. Realizing there was in fact a solid OVC; we briefed the CAT III ILS 35R in addition to our previously briefed CAT I briefing. We never got a chance to ask Tower for current weather before executing the Missed Approach. During vectors for our second approach; we received the current ATIS again; still stating 10SM 120SCT. We were given a different tower frequency this time (Normal freq for 35R). We experienced a solid 06 OVC on this approach. We reported this WX observation to Ground Control after landing. The following night with the same arrival time into Denver; we flew a visual to 35R and were assigned the 133.3 frequency for Tower. I do not know of any deviations on our part. Good weather info would have helped. Not sure what aircraft who caused the RA was doing or had been cleared for; but we were on the localizer for the ILS 35R.

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.