A321
Flight Crew Air Transport Pilot (ATP)
Time Pressure; Distraction; Human-Machine Interface; Troubleshooting
Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Other / Unknown
Air Traffic Control Provided Assistance; Flight Crew Became Reoriented; Flight Crew Requested ATC Assistance / Clarification
Human Factors
This was flying a different arrival then was correct. We were about to start to descend on the arrival when an error message displayed on the FMS stating the ILS runway were mismatched and they did not correspond to each other. This was new to me and I knew I would need to hard tune the frequency which I had read about or never done. About this time we were given a descend via and down we went trying to trouble shoot what was going on; sometime after ATC asked what arrival we were flying because of the altitude and we were re-cleared the correct arrival. And that was that.This goes back to before we took off. We had an unusual deicing because it had been sometime since this station had done it and it was slow. We had to call ground twice once to deice at the gate and the other to taxi. [When we called] for taxi ATC changed our arrival. I believe I changed it but I can't remember but what I did; the FMS was showing the incorrect flight number which was really strange; like it changed itself. That was correct and we left. This was a quick flight and we were busy. Getting close to the arrival myself and the other guy saw the FMS ILS error and both of us moved our attention to this. This was about the time to verify the arrival which I had started to do I even had the correct Jeppesen chart; but because arrivals have almost identical routing to a point that then one goes north the other south; I had seen most of the arrival until the error happened then I was looking at that then came the descend clearance and we found that it was not right. Maybe the FMS error loaded the original route because of the wrong flight number or maybe I simply missed it with the reconfiguration from deicing and with the change in performance numbers. We have a procedure to catch this but I think we fell into the trap of a new error with the FMS and somebody needs to be flying the plane period no matter what. Also this happening at a time right before we check it and the arrivals having near identical structures. This was not an ECAM (Electronic Centralized Aircraft Monitor) just a little amber letters that affect how we were going to land that I had never seen so we both took notice until. Again I believe as we already do that the person who is flying flies period.
Upon arrival we were proceeding via the arrival. Center asked what arrival were on [we realized we were on a different arrival]. We were told to level off and told that we should be on [a different] arrival. Upon further Investigation we realized that we got the change to the [other] arrival on pushback from ground. We obviously did not enter it in to the MCDU (Multi-Function Display Unit). We made the change in the MCDU and continued to a normal landing.There were many factors looking back on the event. It had snowed the previous day and the aircraft that we were taking out had not been decided.  The ground crew successfully deiced the aircraft but it still caused some distraction as it is not something that happens very often. We had the wrong fight number in the FMC and corrected that after pushback. This may have caused us to miss the new arrival that was assigned to us.In climb and cruise we about ready to check and brief the arrival and we had a mismatch in the scratch pad. The distraction with this on a short leg caused us to miss the second opportunity to verify the arrival. Before we could get to the verification we were in ZZZ airspace and that is when ATC questioned our arrival.Route verification is something that we do routinely as our SOP requires however when a change happens it is important to deal with the change as soon as practical to eliminate the possibility of missing it. On a long leg there is time to verify and make sure the arrival is correct.The second point is that on a short leg with a non-normal situation you simply run out of time to verify the arrival and if it is wrong you have the situation that occurred to us. We missed 3 opportunities to verify the arrival due to distraction with flight number change; deicing distraction and non-normal situation in the scratch pad.
A321 flight crew reported flying the incorrect arrival after some distractions both on the ground and in the air.