Date: 201902
Location: ZZZ.Airport, US
Flight conditions: IMC
Weather elements / visibility: Cloudy; Icing
Light: Night
Aircraft: B737 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class C ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Flap/Slat Control System
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; First Officer
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Troubleshooting; Time Pressure; Communication Breakdown; Confusion; Distraction
Second reporter function: Captain; Pilot Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Provided Assistance; Flight Crew Diverted; Flight Crew Executed Go Around / Missed Approach; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Overcame Equipment Problem
Contributing factors: Aircraft; Human Factors
Primary problem: Human Factors

Narrative: After a long flight from ZZZ1 to ZZZ we were on ILS final approach to Runway XXR at ZZZ. We were in the weather with engine anti-ice in use. ATC wanted us to maintain 170 knots until ZZZZZ; so we were keeping the speed up and delaying final configuration accordingly. Approaching ZZZZZ; we selected flaps 15 and up to this point there were no problems. At ZZZZZ; glideslope was captured normally and the aircraft started down the glide path. The PF set '0's' and called for flaps 25. Again; everything was normal. When he next called for flaps 30; the handle was moved but the needle remained indicating flaps 25. Since we obviously did not have a plan; or landing data for this configuration; the PF (Pilot Flying) elected to execute a missed approach. Tower gave us missed approach instructions instead of having us fly the published missed approach and had us contact Departure.During the missed approach procedure; the PF called for 'Flaps 15' but the flaps remained stuck at 25. Once the gear came up; the gear warning horn began to sound and could not be silenced causing an immediate; and significant; distraction. We were not sure that we would be able to return to ZZZ with the current flap configuration. Our planned alternate was IIU. We had plenty of fuel for a normal divert but decided that with the inaccuracy of FMC fuel predictions in this situation that closer would be better. At this point; I became the PF and the Captain switched to PM and began coordinating with Dispatch (ultimately they decided on ZZZ2). Throughout this entire process there were constant interruptions from ATC vectoring us back to ZZZ; wanting to know if we were declaring and emergency; what our plan was; etc. They told us that if we didn't get into ZZZ this time around; then it would be a significant delay before they could fit us back into the sequence. We discussed that; and knew we could not get through the QRH; acquire new data; and coordinate with Dispatch; etc. that quickly. So; we knew we would need to divert. That is when the ZZZ2 decision was made.At that point the QRH was consulted to see what (if anything) could be done about the problem. Upon looking through the Flight Control section; it was inadvertently concluded that there was no check list that applied. I was flying at this point as the Captain worked with Dispatch and checked the QRH. We were initially being held at 3;000 feet. Subsequently; we were climbed to 4;000 feet heading towards ZZZ1. I noticed we were beginning to pick up a good bit of icing so I requested a climb as I knew the ceiling was not that far above us. Initially ATC wanted us to stay down due to arrivals but then found a way to fit us in and get us a climb to 6;000 feet. This got us above the clouds where the temperature was actually significantly higher and the ice cleared rapidly. (Throughout this entire time the gear warning horn was still blaring.)I think the reason it seemed there was no checklist that applied was because the flaps agreed with the handle when the handle was in the flaps 25 position. I think all of the additive conditions made us miss the fact that that while that was true; it was not true when the handle was moved to flaps 30. I think our minds told us 'Well the handle is in 25; and so are the flaps; so that's not the problem' ; couple that with ATC interruptions; the gear horn blaring fuel considerations Icing conditions and contaminated runways; and we just 'missed it'. Reviewing the QRH again we decided to take into account the Trailing Edge Flaps Disagree Checklist; as we felt it was most applicable. Ironically; that is the checklist we needed to run; it just wasn't registering in the brain with everything going on. So essentially; we 'reviewed' the checklist but did not actually 'Run' it. We did what the checklist told us to do; we just didn't 'run' it in the official sense. We knew the anti-ice would be 'ON' during approach to ZZZ2 so we used VREF Ice and flaps 15 for our data (feeling that was most conservative) as the check list said to do and landed uneventfully.


Second narrative: This flight was planned ZZZ1 to ZZZ. We diverted to ZZZ2. On approach to XXR at ZZZ (while configuring) the flaps stuck at 25 degrees. We executed a missed approach. While complying with ATC instructions; FO (First Officer) started looking for correct checklist. I transferred flying duties to FO and started looking for correct checklist. I determined there wasn't one. FO agreed. I retrieved performance for flaps 15 at ZZZ. Due to a thin margin in ZZZ; I asked Dispatch to call Maintenance about preference between ZZZ and ZZZ3. Dispatch suggested ZZZ2. After considering all parameters I diverted to ZZZ2. I retrieved performance for flaps 15 in ZZZ2 for XYL; took over flying duties; and landed uneventfully. After getting home and reviewing the event; I was told I missed the checklist that did apply. Upon review they were correct; I had reviewed the correct checklist; decided it was the wrong checklist and not completed the checklist.


Synopsis: B737 flight crew reported diverting after encountering a flap issue during the approach. The flight crew later determined they did not apply the correct checklist.