Narrative:

To begin with; the descent and approach were planned and briefed prior to top of descent. The clearance was to descend via the crede 3 RNAV arrival for a south landing. Unsure of the runway to expect (16L or 16R) I had briefed flying the arrival with vectors to a visual approach. I expected and briefed the ILS backup for the visual approach to 16L. Between crede and powdr it was necessary to make slight deviations from course to avoid cumulus build ups. ATC was advised. As a result of the off course deviations it appeared that we might have a problem complying with the speed restriction at powdr. We asked for relief from the restriction and were told to comply with the altitude restriction and 'do your best on the speed'. We were in compliance on the altitude; but about 15 knots above the 250 knot crossing restriction and quickly came within speed compliance. After that; the real challenge began. It was becoming obvious that ATC was under the gun. We were handed off to the final controller around mogls. The female controller; speaking very fast; issued us a clearance for an RNAV Z approach to 16R. This was unusual in that in all previous RNAV approaches I've made; it was because we asked for it. Nevertheless; it was unclear what she said with her rapid verbiage; so the first officer asked her to repeat the clearance; which she did speaking even faster it seemed. This is the point where there was misunderstanding between the first officer and me. I believed that she had given us the RNAV Z to 16L and was busy reprogramming the FMC; while the first officer was receiving the approach clearance for the second time. When that was done; and after the first officer was finished on the radio; he asked me to brief the approach. We did it by the book; I briefed all the points from the CDU (FMC) while he verified it on the efb (ipad) chart. There were more radio distractions at the end of the brief. The airport was VMC with good visibility during the approach. I clearly saw the preceding traffic for 16L reported four and a half miles ahead. It was my understanding that I would follow him to 16L. However; the first officer correctly believed our intended runway was 16R. When tower cleared us to land on 16R; I thought that it was a late runway change so I disconnected the autopilot and autothrottles and adjusted my flight path to line up and land on 16R as cleared. It wasn't until later that I was able to determine that we were indeed cleared for the RNAV Z 16R. The first three points: clfff; cepee; and aagee are the same on both approach charts which is why the first officer thought I was briefing the correct approach.the first officer was outstanding in his duties as pilot monitoring. It was because of his diligence in speaking up that we were able to navigate what seemed like a mine field on the arrival. The female controller was; because of her rapid fire clearance; very hard to understand and the pace in which she spoke contributed to the rushed feeling that we all had. RNAV approaches are very helpful and contribute to overall safety when planned and properly briefed in an unhurried environment. If it is the intent of ATC to have everyone flying RNAV approaches; it should be so advised in the ATIS if possible and not given so close in that it can't be properly briefed.

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Original NASA ASRS Text

Title: B737-800 Flight Crew reported misunderstanding an approach clearance to Runway 16R at DEN due to a last minute assignment of an RNAV approach when an ILS or visual was expected. The frequency was also very congested and the Controller was speaking rapidly. The clearance was for the right runway but the Captain heard the left and programed the FMC that way. This error was detected and corrected before a significant deviation resulted.

Narrative: To begin with; the descent and approach were planned and briefed prior to Top of Descent. The clearance was to descend via the CREDE 3 RNAV Arrival for a south landing. Unsure of the runway to expect (16L or 16R) I had briefed flying the arrival with vectors to a visual approach. I expected and briefed the ILS backup for the visual approach to 16L. Between CREDE and POWDR it was necessary to make slight deviations from course to avoid cumulus build ups. ATC was advised. As a result of the off course deviations it appeared that we might have a problem complying with the speed restriction at POWDR. We asked for relief from the restriction and were told to comply with the altitude restriction and 'do your best on the speed'. We were in compliance on the altitude; but about 15 knots above the 250 knot crossing restriction and quickly came within speed compliance. After that; the real challenge began. It was becoming obvious that ATC was under the gun. We were handed off to the Final Controller around MOGLS. The female Controller; speaking very fast; issued us a clearance for an RNAV Z Approach to 16R. This was unusual in that in all previous RNAV approaches I've made; it was because we asked for it. Nevertheless; it was unclear what she said with her rapid verbiage; so the FO asked her to repeat the clearance; which she did speaking even faster it seemed. This is the point where there was misunderstanding between the FO and me. I believed that she had given us the RNAV Z to 16L and was busy reprogramming the FMC; while the FO was receiving the approach clearance for the second time. When that was done; and after the FO was finished on the radio; he asked me to brief the approach. We did it by the book; I briefed all the points from the CDU (FMC) while he verified it on the EFB (iPad) chart. There were more radio distractions at the end of the brief. The airport was VMC with good visibility during the approach. I clearly saw the preceding traffic for 16L reported four and a half miles ahead. It was my understanding that I would follow him to 16L. However; the FO correctly believed our intended runway was 16R. When Tower cleared us to land on 16R; I thought that it was a late runway change so I disconnected the autopilot and autothrottles and adjusted my flight path to line up and land on 16R as cleared. It wasn't until later that I was able to determine that we were indeed cleared for the RNAV Z 16R. The first three points: CLFFF; CEPEE; and AAGEE are the same on both approach charts which is why the FO thought I was briefing the correct approach.The First Officer was outstanding in his duties as Pilot Monitoring. It was because of his diligence in speaking up that we were able to navigate what seemed like a mine field on the arrival. The female Controller was; because of her rapid fire clearance; very hard to understand and the pace in which she spoke contributed to the rushed feeling that we all had. RNAV approaches are very helpful and contribute to overall safety when planned and properly briefed in an unhurried environment. If it is the intent of ATC to have everyone flying RNAV approaches; it should be so advised in the ATIS if possible and not given so close in that it can't be properly briefed.

Data retrieved from NASA's ASRS site 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.