Date: 201901
Local time of day: 1201-1800
Location: ZZZZ.Airport, FO
Flight conditions: VMC
Aircraft: B787 Dreamliner Undifferentiated or Other Model
Operator: Air Carrier
Operating under: Part 121
Mission: Passenger
Flight phase: Takeoff / Launch
ATC / advisory: Tower ZZZZ
Aircraft component: Weather Radar
Reporter organization: Air Carrier
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface; Situational Awareness; Troubleshooting; Confusion; Distraction
Anomaly: Aircraft Equipment Problem Less Severe; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: Other Take off
Result: Aircraft Equipment Problem Dissipated; Flight Crew Returned To Gate; General Maintenance Action; General Flight Cancelled / Delayed
Contributing factors: Aircraft; Weather
Primary problem: Aircraft

Narrative: My weather radar was turned on as we taxied to the runway. On takeoff Runway XXC in ZZZZ; just as the First Officer pushed TOGA; we got a PWS (Predictive Windshear) 'Monitor Radar Display' aural and all the PFD and ND and light associated with the PWS alert system. I rejected the takeoff at maybe 10 knots. We exited the runway. There was no weather; just light drizzle; and no adverse weather or turbulence from other aircraft reported. We determined it was safe to try again. Next takeoff on Runway XXC; as the First Officer was just starting to push up the throttles we got a 'Windshear ahead' aural and all the PFD and ND and light associated with the PWS alert system. Again; I rejected the takeoff and we exited the runway. [Another aircraft] had just departed 5 minutes before us with no reported windshear or turbulence. We then contacted [Maintenance Control] who could find no issues with the aircraft. It was determined we should return to a gate and have local maintenance run some checks. They ran all the checks they could; plus two more that [Maintenance Control] added. In the meantime; I'm chatting with the local maintenance guy; he's telling me about a B787 that did a high speed abort for windshear; the week before; at least he thought it was a B787. We also felt very confident this was not an actual windshear event and my First Officer was wondering if it could have something to with this airports new microwave sensing system. That was all being discussed when Maintenance reported that the aircraft had passed all possible tests and no defects were found. We elected to accept the aircraft. We were released and about to push. I didn't notice that Maintenance had left the weather radar on; and after the door was closed; again we got the PFD and light associated with the PWS alert system; but no aural. We called Maintenance back and they cleared the messages. We start to push again; and again we get the PFD and light associated with the PWS system but no aural. I then noticed the radar was on. I turned it off and the warning displays went away. We decided to run the radar well in advance of takeoff but after engine start. The departure proceeded normally.




Synopsis: B787 Captain reported a rejected takeoff due to a false windshear warning.