Date: 202111
Local time of day: 0601-1200
Location: ZZZ.Tower, US
Flight conditions: VMC
Aircraft: Commercial Fixed Wing
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach; Landing
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Trailing Edge Flap
Component problem: Malfunctioning
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Instrument; Flight Crew Multiengine
Human factors: Time Pressure; Distraction; Workload; Situational Awareness
Second reporter function: Captain; Pilot Not Flying
Anomaly: Aircraft Equipment Problem Less Severe; Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter CFTT / CFIT; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: In-flight
Result: General None Reported / Taken
Contributing factors: Aircraft; Human Factors; Weather
Primary problem: Ambiguous

Narrative: I was flying the ILS XYR approach into ZZZ. The Captain was the Pilot Monitoring. We had monitored and discussed the weather before initial descent. We knew from ATC reports that aircraft were having difficulty landing. Winds were 180/27 gusting to 40 KTS; with good visibility and 4900 ft. ceiling. ATIS also reported gains and losses of 15 KTS on final approach. We planned and briefed a flaps 30 approach with the maximum 15 KTS additive; we spent time discussing the winds and a potential missed approach. Final approach speed was 144 with a target of 159 KTS.Prior to the final approach fix; the wind was fairly steady at 35-45 KTS; with no more than light turbulence. We were instructed to maintain 170 KTS until the FAF. We extended the gear and flaps on schedule and maintained stabilized approach criteria. Airspeed control was manageable with no significant transients. Prior to passing 500 ft.; we encountered a short 10 KTS loss that was countered with power; at that time auto throttles were engaged. The airspeed dropped to 150 KTS before returning to 160. I clicked off the auto throttles below 500 ft. Soon after we had a gain to approx. 175 KTS that persisted. I delayed a power reduction in anticipation of the gust. The speed started dropping back; but stayed near 170.I continued the approach focused on maintaining glide slope and center line. The Captain made two airspeed calls below 500 ft. I was trying to work it back on speed but was concerned about maintaining glide slope with the steep drop off at the approach end of Runway XYR and the expected altitude loss in close. I transitioned and we got a 'Terrain call out. The Captain said continue. I landed the aircraft in the touchdown zone and deceleration was normal. The Captain took control of the aircraft at approximately 80 KTS and cleared the runway. I checked the approach report and flaps at touchdown said 24. The landing was made unintentionally in a non-planned configuration. We taxied in normally and discussed the approach after shutting down at the gate."


Second narrative: First Officer was Pilot Flying; I was Pilot Monitoring. We had monitored and discussed the ZZZ weather extensively before initial descent. Winds were 180/27 gusting to 40 KTS; with good visibility and 4900 ft. ceiling. ATIS also reported gains and losses of 15 KTS on final approach. We planned and briefed a flaps 30 approach with the maximum 15 KTS additive; paying special attention to the winds and possibility of flap relief blow-up and a missed approach.Final approach speed was 144 with a target of 159 KTS. Prior to the final approach fix; the wind was fairly steady at 35-45 KTS; with no more than light turbulence. After starting down the glide path in final configuration; we encountered first a short 10 KTS loss that was countered with power. I saw airspeed drop to 150 before returning to 160. Soon after we had a gain to approx. 175 KTS that persisted. I looked at the flap gauge and saw the flaps reset to 25. Soon after that; the speed started dropping back; but stayed near 170. I expected the flaps to return to 30; and divided my attention between that; the runway and the airspeed. Aside from a few bumps and the gusts; there were no significant deviations from the glide path. At this point we were at approximately 100 ft. over the threshold and I judged the approach to be safe. The First Officer landed the aircraft easily in the touchdown zone and deceleration was normal. I took control of the aircraft at approximately 80 KTS and cleared the runway. I then checked the flap indicator and it was still at 25. I had assumed the flaps had extended to 30; but the landing was made unintentionally in a non-planned configuration. We taxied in normally and discussed the approach after shutting down at the gate.


Synopsis: Air carrier flight crew reported an unstable approach in gusty wind conditions and continued to land. The flap load-relief system retracted the flaps from 30 to 25 when the gust front increased the aircraft's airspeed. After the landing the crew was informed via the data readout that the flaps stayed at 25 throughout the landing; although the crew had intended to extend them to 30.