Date: 201901
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Aircraft: A321
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Takeoff / Launch
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Distraction; Situational Awareness
Second reporter function: Pilot Flying; Captain
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Flight Deck / Cabin / Aircraft Event Illness / Injury; Ground Event / Encounter Other / Unknown
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented
Contributing factors: Human Factors
Primary problem: Human Factors

Narrative: Even though the [takeoff data] was briefed beforehand somehow flaps were set to 1 on the taxi even though planned for 2. Immediately upon ATC contact we were given a runway change and elected to do the taxi checklist later at the end of the runway. We changed the flight plan and I reloaded the box and still hadn't caught that the flaps were in configuration 1 instead of 2 even though the box was set for 2. The taxi checklist was called for below the line and both of us had not realized we never did before the line. This was a huge error as we were hurrying to comply with ATC in getting out in front of a certain aircraft. All configuration tests showed normal. We took off completely normal and the only time we realized the flaps were set to 1 instead of 2 was when the Captain called flaps 1. This event occurred due to multiple distractions at very important phases of the taxi. The way the threat and error model is set up; this should have not occurred; but still did. We were both at a loss at how this could have happened to us when there are multiple checks in place to prevent it from happening.This amount of time myself and the Captain have spent reviewing what happened and replaying the event is a start. There are adequate steps to avoid this and somehow we were distracted at just the right times at every one. There is really nothing more that needs to be done procedure wise; just more attention to detail on our part.


Second narrative: During pushback we were informed by the FAs [Flight Attendants] that a young boy had soiled himself and was in the lav. Expecting a short taxi and not knowing how long he would be; I coordinated with ramp to hold in the alley rather than clog up ground control. We began the checklist by completingthe flight control check at which time ramp asked us to leave the alley for traffic.Ground gave us taxi instructions and a runway change and we proceeded to taxi. Meanwhile the FAs called and informed me the the boy's father was heading to the lav with a change of clothes. I contacted the FAs to inform them we would park in the pad and wait for the family to finish. In the pad we completed the flight plan review after the runway change. The FAsthen called to say they were ready and we completed the taxi items ''below the line' as tower cleared us to line up and wait. Upon departure we realized the flaps were set to configuration 1 when the [performance data] called for configuration 2. Through the numerous calls with ramp; tower; and the FAs we failed to notice the incorrect flap setting. ECAM configuration indications/warnings were normal. Numerous distractions and coordination with FAs; ramp and ground led to breaking up the normal flow of the taxi checklist.I feel that we tried to mitigate distractions by waiting in the alley and then at the end of the runway while the passenger issue was resolved. When the cabin was set I felt in the green not realizing we had passed through a barrier. In the future I will treat distractions the same as we do runway changes in which we review the plan from the beginning and in its entirety. Reviewing the taxi checklist triggers and flows 'from the top' will ensure I haven't bypassed a barrier.


Synopsis: A321 flight crew reported multiple distractions resulted in taking off with the incorrect flap setting.