Date: 202201
Local time of day: 0601-1200
Location: ZZZ.Airport, US
Weather elements / visibility: Icing; Rain
Aircraft: B767-300 and 300 ER
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Taxi
ATC / advisory: Ground ZZZ
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Human factors: Communication Breakdown
Second reporter function: Dispatcher
Anomaly: Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control; Ground Event / Encounter Weather / Turbulence; Ground Excursion Taxiway
Detector: Person Flight Crew
When detected: Taxi
Result: Aircraft Aircraft Damaged; Flight Crew Regained Aircraft Control; Flight Crew Returned To Gate; General Maintenance Action
Contributing factors: Procedure; Weather
Primary problem: Weather

Narrative: XA:30 engine start. Taxi instructions [Taxiway] XX; cross Runway XX; left on [Taxiway] XY. I performed a brake check while taxiing on [Taxiway] XX. Brakes were good. Crossed runway and turned left on [Taxiway] XY. Advanced power to accelerate a bit in order to do another brake check on Taxiway XY. I applied the brakes and could feel pressure; but had poor braking action which was very alarming because we just had good action not 5 minutes beforehand. I was left literally speechless...at that point I realized I had left the power up and immediately brought power to idle; released brakes fully and then rapidly applied brakes; to good effect....and then the brakes gave way again to poor braking action. By this time the bend in the taxiway was approaching; I released brakes and reapplied brakes; again to good effect initially; and then nothing....I brought the tiller around to try and make the turn; no effect; Immediately centered the tiller; rev thrust; and accepted the 'off'. I was able to steer with the tiller and gently brought the plane back up onto the taxiway fully. Set the parking brake. Called for help. Towed back to the line.Rapidly deteriorating conditions at the airfield due to a sudden drop in temperatures coupled with freezing precipitation. Taxiways were only chemically treated and the sand truck had not been down Taxiway XY yet; I did not know this at the time we were taxiing. Obviously I was taxiing too fast for conditions.Obviously a slower taxi speed was warranted. Conditions were deteriorating rapidly; I should have confirmed with Ground about the status of ground efforts to treat the runways and taxiways. Slowing down the tempo of operations would have also helped. My FO (First Officer)and I talked about everything that we were doing and we both felt comfortable as we were proceeding. It wasn't until we were on Taxiway XY that things went badly; and quickly.


Second narrative: Aircraft Incident: Flight departed the ramp eastbound on Taxiway XX crossing Runway XX and turned north onto Taxiway XY and proceeded down Taxiway XY to depart from Runway XX just after crossing Taxiway XZ. On [Taxiway] XY the a/c (aircraft) started to slide and the left main gear and nose wheel went off the taxiway into the grass. The crew was able to regain control of the a/c and return it to the taxiway. The a/c was towed back to the gate and MX performed an inspection and found damage to the left wing leading edge slat. Per the Flight Crew: Rapidly deteriorating taxiway conditions due [to] light freezing rain.


Synopsis: B767 flight crew and Dispatcher reported a taxiway excursion due to freezing rain and worsening weather conditions.