Date: 201503
Local time of day: 1801-2400
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: Rain; Snow; Windshear
Light: Night
Aircraft: B777 Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Final Approach
Airspace: Class B ZZZ
ATC / advisory: Tower ZZZ
Aircraft component: Trailing Edge Flap
Component problem: Improperly Operated
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Human factors: Workload; Physiological - Other; Distraction; Confusion; Communication Breakdown; Fatigue
Second reporter function: Pilot Not Flying; Captain
Anomaly: ATC Issue All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Unstabilized Approach
Detector: Person Flight Crew
When detected: In-flight
Result: Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Contributing factors: Weather; Human Factors; Company Policy
Primary problem: Human Factors

Narrative: This was an all-nighter with a hotel pick-up time several hours before midnight. I had planned an afternoon nap; but being a night owl and having slept fairly well the night before; was not able to get any sleep. Flight went fine; ate lightly; but started to feel quite tired about 1 hour from landing. Consumed a coffee drink at that point in an attempt to be alert.Briefed the planned approach and go-around procedure as per SOP. The ATIS weather was light snow with possible strong crosswinds (030@14 Gusts to 24) so planned Flaps 25 and auto brakes level 4. ATC communications were busy and we were vectored to approximately a 12 mile final. We were told to keep our speed up (170 kts) to the final fix. At that point we had the gear down and Flaps 20. The Tower was very busy and the Captain was trying to get a landing clearance. I asked for Flaps 25 but apparently was too tired to note that he didn't hear me and did not move the Flap handle. At 500 feet; I finally noticed the flaps were still at 20; and again asked for 25.What I should have done was GO-AROUND!!! In our fatigue; the Captain and I were both so focused on landing that neither of us thought or vocalized that we were outside of the definition of a stabilized approach. Yes; the plane was in final configuration and at the proper speed for landing; but not until below 500 feet. I can't believe after years of reading the Quality Assurance reports and thinking how could a pilot do something so stupid; now I understand. I have met the moron and he is ME!


Second narrative: This was an all-night flight. FO was flying. We were both tired (fatigued) as we began ILS APP to 35L; with blowing snow. As nonflying pilot I was trying to get landing clearance taking a lot of my time. As we approached approximately 600 feet AGL I noticed the flaps were not set to final Flaps 25. FO may have called for them. However I did not hear the call. Flaps were set to 25 and normal landing was accomplished. In my opinion with fatigue being a concern a go-around was not the best option. I know I was tired.


Synopsis: A fatigued B777 crew failed to execute a missed approach when they discovered flaps 25 were not set at 600 feet AGL. Flaps 25 were set for landing.