B737 Undifferentiated or Other Model
Flight Crew Air Transport Pilot (ATP)
Flight Crew Last 90 Days 167; Flight Crew Type 2590
Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Taxiway
Flight Crew Returned To Gate
Airport
While taxiing to runway we encountered a sheet of ice and I lost control of the aircraft. I had the brakes applied and #2 thrust reverser deployed (#1 thrust reverser was MEL'd). The taxiway sloped downward and the aircraft exited the taxiway and came to rest in the snow. Airport subsequently closed due to the nil braking and the other aircraft behind us was towed back to the gate.
During taxi we heard a Mu report (first Mu report received) for [our] runway and decided to pull over into hold area to evaluate and assess risk of Mu report. As aircraft was turned toward hold area; braking was immediately ineffective; braking action was nil. Captain applied reverse thrust (engine 2 only; engine 1 was MEL) and stayed on brakes. Front of aircraft departed prepared surface of hold area at very slow speed. Responding vehicles also reported braking action as nil. Airport then closed due to nil braking.
B737 flight crew reported encountering nil braking action on taxi out that resulted in a taxiway excursion.