Medium Transport; Low Wing; 2 Turbojet Eng
Flight Crew Air Transport Pilot (ATP)
Time Pressure
Deviation - Speed All Types; Inflight Event / Encounter Fuel Issue; Inflight Event / Encounter Unstabilized Approach; Inflight Event / Encounter Weather / Turbulence
Flight Crew Executed Go Around / Missed Approach; Flight Crew Landed As Precaution
Weather
The flight started normally. My First Officer (FO) and I discussed the weather surrounding COS before and during the flight. Noticeable virga was on the approach end about 10 miles north of 17L. The airport was not reporting windshear or wind gusts on the last ATIS. A flaps 45 landing was used on the first approach. A red windshear appeared and we executed a go-around. I am not sure; but we may have gone over 200 kts during the go-around in Class C. The weather was still VFR for COS and the storms were moving away from the airport. The weather had thunderstorm activity between COS and our filed alternate. A quick discussion of our options resulted in another attempt to land at COS. On the second approach; we used a flaps 22 landing. Another red windshear appeared and we once again executed another go-around. Our best option still appeared to be another attempt to land at COS; but on the third attempt I flew the approach. For the third time; we got another windshear warning that quickly went away along with a soft 'sink rate; sink rate'.With the fuel running low; a flight to DEN would have put us in a min fuel status and there was weather that would require additional vectors off course. On all three approaches; the windshear felt minimal and I did not expect to get a windshear message with the storms at its distance away from the field. Although we were told the storms were moving away from the field; I did not want to risk having the storm change directions and further limit our options. Also; the windshear message went away and I adjusted the aircraft to not allow another sink rate aural message. After quickly reviewing our options; we agreed to continue the approach and land in the interest of safety. The aircraft was fully configured above 1000 AGL and no aircraft limitations were exceeded; although I was fast on the approach. The threats included windshear; thunderstorms in the vicinity; thunderstorms enroute to our filed alternate; thunderstorms approaching our filed alternate; a high workload environment; and a steadily decreasing amount of fuel.
After a normal flight with myself as pilot flying; during our arrival brief the Captain and I briefed the possibility of a go around  due to a small thunderstorm north of the COS airport and the steps involved in go around. Our alternate was DEN with thunderstorms expected in the vicinity. As we approached the field; still with approach control; we visually saw the thunderstorm which was about 6 miles north of the 17L runway. Approach informed us about the thunderstorm as well and said no aircraft had any issues with getting in and no unusual weather alerts were given. It was my leg to fly; the Captain and I briefed the risks and that we would need to be fully configured early to avoid an unstable approach. This would be a flaps 45 landing. Flaps 8 was called for early and then gear down and flaps 22 was called for on our extended left base and inside outer marker. Turning final; I asked for flaps 45 and landing check. I was a little high and corrected and was stabilized by 1000 feet; I believe about 1 to 1.5 miles from the end of runway we received a Windshear red alert; thus we executed a go-around. We climbed out to our assigned altitude and reconfigured; briefed what happened and I quickly asked either the tower or the approach control; what direction the thunderstorm was moving; they said storm was basically moving ENE away from the field. The Captain and I briefed the approach and landing again; believing that it was safe to execute another approach and landing; but instead using flaps 22. We executed the approach with the same result; a Windshear almost in the same spot. We executed a go around and after a quick discussion and review of the weather and weather at the alternate; I transferred the controls to the Captain so he could execute the approach in the interest of safety. We briefed the weather/risks; approach and landing; and executed a flaps 22 landing with the same results; a Windshear warning; however; the warning was only on for a matter of maybe 2 seconds and went away then a soft sink rate; however quickly went away. After a quick discussion we both felt the safest option was to land the aircraft. The short final was stable; however fast (which was briefed) and we landed with no further issue. At no time did I feel nervous or that we were operating in a unsafe manner. I believe the Captain acted and operated in the most professional manner. Threats included windshear; thunderstorms in the vicinity; thunderstorms enroute to and at our alternate; a high workload  environment and a always decreasing amount of fuel. After first approach and go around we could have diverted to our alternate; however before we even left ZZZ I checked the radar and Denver had thunderstorms building to the west and south west and also Pueblo would normally be a good alternate but they had storms as well. We could have diverted to the alternate with the same results; but with landing with even lower fuel. We could have executed a hold but; according to controllers; the storm was not moving much.
Flight crew reported windshear warnings while attempting to land at the COS airport that resulted in two missed approaches. A third attempt was attempted in lieu of a diversion; and a successful landing was accomplished.