Date: 201202
Local time of day: 1201-1800
Location: COS.Airport, CO
Flight conditions: VMC
Weather elements / visibility: Windshear
Light: Night
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Initial Approach
Airspace: Class C COS
ATC / advisory: Tower COS
Reporter organization: Air Carrier
Reporter function: Captain
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Situational Awareness
Second reporter function: First Officer
Anomaly: Deviation / Discrepancy - Procedural Published Material / Policy; Inflight Event / Encounter Fuel Issue; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Aircraft Other Automation; Person Flight Crew
When detected: In-flight
Result: Flight Crew Diverted
Contributing factors: Human Factors; Weather
Primary problem: Weather

Narrative: [We were] released with VFR weather and a planned arrival fuel of 5.8. We waited about 25 minutes to depart and the winds were slightly stronger than forecast at cruise. Approximately 120 miles; showing landing fuel of 4.6; we are told to expect 18 minutes of holding due to high winds. We immediately got the plan going to divert with Dispatch via ACARS; which we employ shortly with ATC and were let down into COS. COS is busy but uneventful as we coordinate for all required to divert and land off-station. Winds on TAF for Springs were forecast to pick up and become gusty out of the northwest at our arrival time and they did just that. LLWS was on ATIS and was briefed with appropriate speeds at Ref + 18. Fully configured and about 1;200 FT-1;500 FT AGL; we get a full Windshear Warning with a 'go around' command. The First Officer and I quickly analyze the situation; our fuel; long length of the planned runway; current flight parameters; probability that the LLWS condition is going to stay and probably increase based on the forecast; current fuel insufficient to fly to DEN; which has the same conditions and more traffic; and the fuel state we would have after a lap around the patch with likely the same conditions to greet us on final; and elected to continue with the option of a go-around if the situation warrants. We were going to have to land at COS as I did not see any other viable alternative given our situation. We had talked about most of these considerations prior to our approach. The ride down final was turbulent but controllable with +/- 10 KTS airspeed; slight pitch; roll and yaw oscillations. The conditions were not as pronounced as those we encounter in our simulator windshear training. Touchdown was slightly long and; after normal braking; we turned off around 5;000 FT of runway remaining. We shut down on the ramp with 4.1 on the gas. More fuel; it's too long of a flight to not have a bit more of a cushion. I should have questioned this more. The DEN weather was VFR; but I didn't fully consider the implications of the wind and possibility of delays.


Second narrative: [We] took off at minimum takeoff fuel. Top of Climb winds were higher than planned and enroute winds were higher than planned. [We] showed arrival fuel for Runway 26 at 4.6. Then; we were told to plan on holding at Denver due to winds. We emailed Dispatch and told them we had no fuel to hold. Received and acknowledged a divert plan. COS winds at the time were calm with TAF winds getting bad; gusting in our arrival time frame. COS winds on TAF showed they would get worse; not better. COS Approach and Tower were reporting many windshear alerts from the time we checked in. We planned on an approach to 35L and the system showed our arrival fuel at 4.1. Inside the FAF; we received a Windshear Warning from the northwest quadrant. It was a momentary warning but we both know we were supposed to go around. We elected to continue the approach and go around if conditions warranted since we would be at emergency fuel and have to shoot the same approach again to the same runway anyway. Landing was bumpy but uneventful. We shut down with 4.1. After landing; in addition to windshear alerts; Tower reported many microburst warnings; so I believe we made the right move in retrospect.


Synopsis: A B737 flight crew reports diverting to COS due to delays into DEN and a low fuel situation. Windshear alerts are reported at COS and the aircraft generates a windshear warning during approach at 1;200 to 1;500 FT. The crew elects to continue after considering fuel and the likelihood of windshear becoming worse. A safe landing ensues.