Narrative:

I was PF (pilot flying) into ZZZ; an airport I have been to very infrequently; perhaps a total of 6 times; the most recently being at least 6 months ago. Our clearance was the zzzzz arrival; which is runway-dependent in the sense that there is a zzzzz landing both east and west. The ATIS was advertising the ILS/visual to xxl and RNAV/visual xxr; as the ILS xxr was NOTAM'ed out-of-service. Because we were approaching ZZZ from the south; the FMS was programmed with the ILS xxl. However; upon initial contact with arrival (approach) control; we were assigned xxr and the FMGC (flight management guidance computer) was changed to RNAV xxr. I confirmed this before it was executed and then proceeded to independently verify the STAR's speeds and altitudes were still correct. Not only was this taking place below 10;000 ft.; ATC began to get busy and a light twin appeared on TCAS approximately 2;000 ft. Below our nose. We visually acquired the aircraft and not long thereafter; ATC issued us an immediate right turn and instructed a level-off. I assumed this was to prevent a traffic conflict with the aforementioned light-twin until ATC stated that our clearance limit was the zzzzz and we had not been cleared for the RNAV. It was then I realized my gross error. In loading the second approach; the RNAV xxr had auto-strung and I failed to catch that we should not have allowed that to happen. Contributing factors: I have been flying to ZZZ quite a bit this summer and executing RNAV approaches that we do auto-string. I believe this led to an expectation bias. Also; the first approach loaded (the ILS) had not auto-strung; so I was not in the mental mode to be 'on the lookout' for it. My attention was also distracted with attempting to visually acquire the light twin. But the bottom line is this is instrument flying and I did not catch my mistake until it was pointed out to me.

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Original NASA ASRS Text

Title: A319 Flight Crew reported an automation mismanagement resulting in a course deviation.

Narrative: I was PF (Pilot Flying) into ZZZ; an airport I have been to very infrequently; perhaps a total of 6 times; the most recently being at least 6 months ago. Our clearance was the ZZZZZ Arrival; which is runway-dependent in the sense that there is a ZZZZZ landing both east and west. The ATIS was advertising the ILS/Visual to XXL and RNAV/Visual XXR; as the ILS XXR was NOTAM'ed out-of-service. Because we were approaching ZZZ from the south; the FMS was programmed with the ILS XXL. However; upon initial contact with Arrival (Approach) Control; we were assigned XXR and the FMGC (Flight Management Guidance Computer) was changed to RNAV XXR. I confirmed this before it was executed and then proceeded to independently verify the STAR's speeds and altitudes were still correct. Not only was this taking place below 10;000 ft.; ATC began to get busy and a light twin appeared on TCAS approximately 2;000 ft. below our nose. We visually acquired the aircraft and not long thereafter; ATC issued us an immediate right turn and instructed a level-off. I assumed this was to prevent a traffic conflict with the aforementioned light-twin until ATC stated that our clearance limit was the ZZZZZ and we had NOT been cleared for the RNAV. It was then I realized my gross error. In loading the second approach; the RNAV XXR had auto-strung and I failed to catch that we should not have allowed that to happen. Contributing factors: I have been flying to ZZZ quite a bit this summer and executing RNAV approaches that we do auto-string. I believe this led to an expectation bias. Also; the first approach loaded (the ILS) had not auto-strung; so I was not in the mental mode to be 'on the lookout' for it. My attention was also distracted with attempting to visually acquire the light twin. But the bottom line is this is instrument flying and I did not catch my mistake until it was pointed out to me.

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.