Date: 201412
Local time of day: 1801-2400
Location: SFO.Airport, CA
Flight conditions: VMC
Light: Night
Aircraft: B737-800
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Initial Approach
Airspace: Class B SFO
ATC / advisory: Tower SFO
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface; Situational Awareness; Workload; Distraction
Second reporter function: Pilot Not Flying; Captain
Anomaly: Deviation - Speed All Types; Inflight Event / Encounter Weather / Turbulence; Inflight Event / Encounter Unstabilized Approach
Detector: Person Flight Crew
When detected: In-flight
Contributing factors: Weather; Company Policy; Airport
Primary problem: Weather

Narrative: SFO was experiencing unusually high winds out of the north; and were actually landing using Localizer 28L until after the San Mateo Bridge; and then circle to land on Runway 1R. The visibility and ceiling were perfectly VFR; so it was just the winds (gusting to 44 knots when we were there) that were causing all the complication and delays that day. We knew to expect this and I had actually already been through this same approach earlier that day on a -700 as Pilot Monitoring; during daylight with a different Captain. Now it was night time and the winds were a little stronger but still right down Runway 1R. To be honest; I think this approach is not a safe way to conduct operations. During the day it's a little less troubling; but at night it is amazing that this was even being suggested. That's easy for me to say now. There is no guidance to this runway of any kind. We built a fix in the FMC on a two-mile final because we weren't comfortable with a more traditional three-mile fix due to the terrain. I configured very early and due to the fact that we were in an -800 and we had known 20 knots gusts; we had an OPC computed target speed of 165 knots. Obviously; very fast; and so we briefed the nature of our relationship to the flap speeds.I flew the visual approach with the aid of the terrain display and VNAV PATH as a reference; however; I was hand flying with the Flight Director off as I had no legal FMC data to use for guidance. All in all; I was at or above target and at or above the path to the runway. The problem arises when the gusts started to exceed the flap speed for flaps 30 and the flaps did what they are supposed to do and automatically retract to flaps 25. We continued. We should have gone around and frankly; SFO should probably not have been conducting approaches. We continued and landed on 1R. We taxied to the gate and that was that. I'm writing this; and my Captain is too; because I know it was wrong. The GPWS Too Low Flaps sounded when the flap blow up feature did its job; and we didn't respond as we should have and executed a go-around. There isn't even a PAPI or VASI to guide you once you're on final. I know better than this; and know that I will be talking to somebody about this.To be honest; I think there were probably a lot of reports written that day. It was a dumb approach to do during the day; and at night it should probably be policy that Company just doesn't do it. We talked to a Captain from another carrier the next morning at the hotel; and he said they just diverted because their Company policy doesn't allow landing on Runway 1L or 1R. I'm not trying to dodge the fact that I didn't adhere to procedure and should have gone around; which would have ended up being a diversion as well. My thoughts are; and the reason I feel confident saying that other safety reports were probably filed that day; is because I don't think there is a right way to shoot a tight; circling approach; with no guidance; and gusts beyond your flap limitations; at night without breaking the rules. Can it physically be done? Probably; but not consistently. Is it a smart thing to do? Absolutely not.


Second narrative: First Officer turn to fly; enroute we discussed at length the concerns of the visual circle without approach guidance on final; rising terrain on base leg; etc. Captain built a visual ground track in FMC/CDU. Once initiating the breakoff from the 28 ILS; and maneuvering to a base position for 1R; Captain reloaded CDU to Runway 1R for path guidance on straight-in final.We got momentary blow-up of the flaps to 25; and 'Too Low Flaps' Warnings on final approach. Realizing the warning was airspeed related; and that we had sufficient airspeed for the momentary flaps 25 condition; I told the First Officer to continue (the approach) and work on bringing the airspeed back down in range (which allowed the flaps to track back to 30).


Synopsis: A B737-800 flight crew flying a night; performed a circling approach to Runway 1R; off the 28L localizer. Due to high and gusty winds; the pilots received a; 'too low flaps;' EGPWS warning when gusts momentarily increased IAS above the flaps 30 limit and they 'blew back' as designed. They continued the approach and; as the gust moderated; the flaps returned to 30 and the warning ceased.