Date: 201510
Local time of day: 1201-1800
Location: DEN.Airport, CO
Flight conditions: VMC
Weather elements / visibility: Windshear
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Takeoff / Launch
Airspace: Class B DEN
ATC / advisory: Tower DEN
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: ATC Issue All Types; Inflight Event / Encounter Weather / Turbulence
Detector: Automation Air Traffic Control; Person Flight Crew
When detected: In-flight; Taxi
Result: Air Traffic Control Issued Advisory / Alert; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Took Evasive Action
Contributing factors: Procedure; ATC Equipment / Nav Facility / Buildings; Airport
Primary problem: Ambiguous

Narrative: As we approached Runway 8 in DEN for takeoff; Tower cleared a flight ahead of us for takeoff and told them that they had a windshear alert over the runway. That flight continued takeoff. I told my FO that if they try to clear us for takeoff; that we can't go with a windshear alert on airport. Sure enough; they cleared us for takeoff and we told them we can't go with a windshear alert on airport. They cancelled our takeoff clearance and told us to clear off to the holding area. They then asked a flight behind us if they could takeoff; and that flight told them to standby. I then started to ask for more information about the windshear alert. Tower said he had the alert since he had been there. I asked if the system was malfunctioning and if they had someone looking into the system. Tower wasn't sure and then said that the alert had been there most of the day.Tower asked the aircraft that just took off if they experienced any windshear; they said no. The aircraft behind us then said that they could takeoff. I told my FO that we would see what that flight sees before we make our decision. In the meantime; I turned on the weather radar and pointed our nose toward the departure end of the runway to check things out; no issues. I told my FO we would also do the 'adverse takeoff' profile just to be safe. After the second aircraft was cleared for takeoff; Tower asked them if they encountered windshear; they said no. Given everything we had heard/seen; we told Tower we were good now and Tower cleared us for takeoff and issued winds but did not issue us a windshear alert. During takeoff; we did experience a momentary increase of about 15-20 knots passing about 200 feet AGL. Passed that information on to Tower and continued flight.ATC needs to take windshear alerts a little more seriously. Even in VMC; being at the base of the Rockies; windshear is always a concern. If Tower is getting a consistent alert that does not seem to make sense; then they need to look into their systems.


Second narrative: We were taxiing behind another carrier aircraft and Tower cleared them for takeoff and told them they had a windshear alert of a gain of 20-25 knots right over the runway. The other carrier then continued the takeoff while they cleared us to line up and wait. We then told them that we did not believe we could takeoff because of the windshear alert. Ironically; we both remembered that it was a question on the check ride study guide. We then got into the EFB to find the procedures. The other carrier reported no windshear and the Tower cleared a second aircraft for takeoff behind us. They took off and reported no windshear.We asked Tower if they believed that there was an equipment malfunction. They responded that it's been like that all day. Then; we asked if they were going to remove the warning. He said it still shows the windshear. We then prepared the aircraft for an adverse weather takeoff and briefed the windshear recovery procedure if necessary. A female Controller then came on and cleared us for takeoff without the windshear alert. We took off and encountered a brief 20 knot increase at 100 feet AGL. We did not need the windshear recovery because it was momentary. We reported it and continued on.Tower needs to take this more seriously! The Controller did not seem to care about clearing aircraft for takeoff despite his equipment saying that there was a windshear on the field! His tone of voice seemed to indicate that he was about to come off shift and didn't care what possible dangerous situation he was putting aircraft in. This was totally unacceptable.


Synopsis: During taxi to takeoff; a B737-700 flight crew reports being informed by the Tower of a windshear alert. The next aircraft is cleared to takeoff and does so without issue. The reporters elect to delay their takeoff and query the Tower for more information. The Tower indicates the system has been alarming all day and the crew elects to depart and encounters a 20 knot increasing headwind at 200 feet AGL.