Date: 202009
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Weather elements / visibility: Windshear; Turbulence
Light: Night
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Landing
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Not Flying
Reporter qualification: Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness; Distraction
Anomaly: Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence; Inflight Event / Encounter Unstabilized Approach
Detector: Automation Aircraft Terrain Warning; Person Flight Crew
When detected: In-flight
Result: Flight Crew Executed Go Around / Missed Approach
Contributing factors: Environment - Non Weather Related; Human Factors
Primary problem: Human Factors

Narrative: This event was undoubtedly the most humbling and perhaps a first in my almost XX years with (airline) and going on X years as Captain.  While there will always be a first; it will certainly serve as a professional learning opportunity for me personally.  I take full accountability as Captain for not directing a go-around sooner.  The ZZZ1-ZZZ flight was leg three on a three day pairing.  We were approaching an 8 hour flight block and over 10 hour duty on our flight to ZZZ. Flight paperwork review prior to departure indicated weather conditions which ended up being inconsistent with what we encountered in ZZZ.  Due to an ATIS outage that had spanned several hours; we were only able to retrieve hourly METAR reports for ZZZ. The last hourly report indicated significant changes with respect to gusty crosswinds from the East with smoke slightly lowering visibility.  As it came close to time to brief; I sent a message to Dispatch inquiring about ZZZ ATIS.  The message we received back indicated there indeed was an outage.  Unfortunately we were out of range to obtain the VHF ATIS prior to our briefing; but later obtained ATIS information over VHF in our descent.  Prior to TOD; we briefed the approach that we anticipated in ZZZ; the visual backed up by the ILS for [Runway] XYR.  We discussed relevant threats of gusty crosswinds; night; fatigue and potential for arrival changes and runway re-assignment. I set up with the VSD to be able to monitor flight path. On initial hand off to ZZZ Approach; we were assigned Runway XYL.  As PM; I loaded  the approach for the ILS XYL in the FMC; set new baro minimums; entered the new runway data; and set up the NAV frequency/course for XYL; briefed the changes; and then ran the change triangle Descent checklist. Approach Control directed us to go direct ZZZZZ on the approach; maintain 4;000 until ZZZZZ; and were subsequently cleared for the approach. My FO as PF attempted to mitigate the threat of being high on path maintaining higher speed as directed previously by ATC (delete speed restrictions on the arrival) and I monitored using the VSD.As we joined final; it was evident from wind data on the PFD; that the winds on approach were strong challenging gusty crosswinds from the East.  After joining final for XYL; my FO struggled with maintaining the LOC course and GP with the gusty dynamic crosswinds.  With LOC and GP deviation call outs as PM; my FO did an outstanding job re-establishing proper path and we were able to achieve what we thought was stable criteria.  In the time frame of attempting to get better alignment established on final and simultaneously run the landing checklist; I inadvertently missed the final flap 30 selection; and we both missed the flap misconfiguration on the checklist.  While we ran the landing checklist; our attention was diverted enough to not note the flaps 25 configuration.  Cumulative fatigue from a long flying day with challenging weather contributed to the inadvertent omission.  It wasn't until the GPWS Flaps alert that we noted the misconfiguration.  Out of concern for speed due to gusty winds; I selected flaps 30 just as I directed the go-around due to unstable landing criteria.  While I normally look at flap configuration at the 500 feet gate as an additional check; the cumulative fatigue and dynamic wind conditions had my attention more focused on monitoring winds and flight path.  After having time to reflect on the encounter; the wisdom it has imparted is the absolute importance of an early go-around if conditions are not coming together as planned for an early stable approach. A go-around at 1;000; due to challenges with flight path would have afforded an easier go-around scenario with dynamic gusty winds after 8 hours of cumulative flying for the day.While we both had no currency issues and had sufficient recent experience; it's undeniable that pairing constructions that culminate in 8-9 hours of block time landing close to midnight on day threeof a trip that consisted of two to three legs every day with aircraft swaps only add to fatigue.  In this new era of COVID; there are added stresses which only serve to raise the overall underlying level of surge fatigue that exists from operating on the front lines and dealing with constant change.  While I take full accountability for my actions and omissions; I have concerns over the impact of future pairing construction given my recent encounters.With respect to lessons learned; our encounter highlights the importance of an early go-around in dynamic weather conditions when the approach is not coming together as planned.  As mentioned in the narrative; it's undeniable that pairing constructions that culminate in 8-9 hours of block time landing close to midnight on day three of a trip that consisted of two to three legs every day with aircraft swaps only add to cumulative fatigue.  We are operating in a new normal; and pairing design and construction should consider the added underlying level of fatigue and operational stress that cannot be easily mitigated.  Pairings with a 3-2-3 leg-day design with multiple aircraft swaps should be strongly avoided so as to not be conducive to creating conditions ripe for encounters such as the one described above.




Synopsis: Air carrier Captain reported a flap misconfiguration leading to an unstablized approach and go-around.