Regional Jet 900 (CRJ900)
Flight Crew Air Transport Pilot (ATP)
Confusion; Situational Awareness; Workload
ATC Issue All Types; Conflict Airborne Conflict; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Flight Crew Became Reoriented; Flight Crew Returned To Clearance
Human Factors; Procedure
While operating to CLT; we were descending via the IVANE 5 RNAV arrival. This arrival involved numerous step down crossing restrictions including several windows of altitude; requiring my full concentration. Before starting the arrival; I briefed a visual approach to one of the three arrival runways advertised on the ATIS (36C). While on the arrival; CLT approach assigned us a different runway than what we had briefed. The Captain requested the runway I had briefed (36C); with ATC as we had that ILS approach loaded in the FMS; and would mean a shorter taxi. ATC said they had our request. At that point the Captain loaded the new runway into the FMS; and I gave a quick brief for the new runway. When we were on a right downwind; we were handed off to another Approach Controller; who assigned us the original runway I had briefed (36C). The Captain then started reloading the ILS 36C into the FMS; and switched back to the proper localizer frequency. Just then; ATC gave us a base turn. While making the turn; I saw another aircraft in front of us; on final for what I thought was 36R. After we called the CLT airport in sight; ATC gave us a heading to join the localizer and cleared us for the visual approach. I then bugged that heading and armed the approach mode of the autopilot; while still watching the aircraft in front of us. While I still had the airport in sight; we were more focused on this aircraft in front of us because of its proximity to us. I noticed in my scan that the autopilot had captured the localizer and was turning to join it. I looked back up to the traffic to monitor its position relative to us. When we were nearly directly behind the aircraft; I noticed that the autopilot had overshot the 36C localizer and that this traffic we were seeing was actually on final for runway 36L. I disengaged the autopilot and promptly corrected for the overshoot while the Captain notified ATC. We did not get a TCAS TA or RA. ATC responded by calling the traffic to us (12 o'clock and one mile) and simply told us to continue the right turn to rejoin the 36C localizer and to descend from 4;000 ft. to 3;000 ft. About 10-15 seconds later we were established on the 36C localizer and continued the approach to a normal landing.Because we were approaching from the East; and the traffic in front of us seemed to be in close proximity to us; I incorrectly thought that the traffic was on final for runway 36R. Consequently; I was expecting to pass behind them since we were crossing the 36R localizer to join the 36C localizer. Without this bias; I may not have fixated on this traffic so much; and would have exercised a broader scan that better included the CDI needle.I think another reason I was tempted to visually look out the windshield was the combination of a high workload; and a runway assignment change; which rendered much of the information on my EFIS screen temporarily invalid. Even after the correct runway was programmed into the FMS and proper localizer frequency tuned; I continued focusing on the traffic more than I should have. Additionally; I don't recall ATC calling this traffic to our attention. If they had told us that the traffic in front of us was on final for runway 36L; it may have helped my situational awareness because I would have known that we would not be passing behind them.
CRJ-900 First Officer reported overshooting the extended centerline on approach to CLT after several runway changes.