B777-200
Flight Crew Air Transport Pilot (ATP)
Aircraft Equipment Problem Less Severe
Flight Crew Rejected Takeoff; General Flight Cancelled / Delayed; General Maintenance Action
Aircraft; Procedure
During the takeoff roll approximately 100KIAS a windshear warning was received. The takeoff was rejected; reverse thrust was not used and we exited the runway without further incident. We were directed to a hard stand where our local maintenance crew boarded the aircraft and proceeded to complete the required tasks following a high speed abort. After brake cooling;refueling and filing a new flight plan we taxied to runway 29 for takeoff. Winds were reported 240 @ 6K. at approximately 65KIAS another windshear warning was annunciated and the takeoff was discontinued. After consulting with maintenance the decision was made to [defer the windshear warning system]. At the time we were all in agreement the system was unreliable. We returned to runway 29; took off and completed the flight with no further incident. A maintenance supervisor met the flight and I debriefed him in detail. I conveyed to him that the crew had no way of validating the windshear warning system. Since all other airplanes were taking off and landing normally that night; in our best judgement it was safe to takeoff and complete the flight.
Storms enroute caused weather deviations and vectors...for sequencing into destination added time. We ultimately exceeded our flight duty time by 8 minutes.I personally will be more conservative in the future and insert a more substantial personal buffer for both flight time and duty day limitations to alleviate the potential for a future issue. This perspective would adversely effect operations if widely adopted.
A B777 flight crew experienced two sequential incidents of apparently fallacious wind shear alert warnings on takeoff roll for an international flight.  The system was subsequently deferred but the flight; delayed enroute by weather; ultimately exceeded the flight crew's legal duty time.