Date: 201304
Local time of day: 0001-0600
Location: RST.Airport, MN
Flight conditions: Marginal
Weather elements / visibility: Snow
Light: Night
Aircraft: Large Transport
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Flight phase: Taxi
ATC / advisory: Ground RST
Reporter organization: Air Carrier
Reporter function: Captain; Pilot Flying
Reporter qualification: Flight Crew Air Transport Pilot (ATP)
Human factors: Human-Machine Interface; Situational Awareness
Second reporter function: Pilot Flying; First Officer
Anomaly: Ground Excursion Taxiway
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Became Reoriented; General Maintenance Action
Contributing factors: Human Factors; Weather; Airport
Primary problem: Ambiguous

Narrative: First Officer was pilot flying; uneventful flight; approach and landing. RST Runway 31 in use; condition of Runway 31 was center 50 FT plowed with good braking action; remaining width of runway braking action poor. The taxiways were snow covered; edge lights were visible but taxiway markings and center lines were not visible due to snow cover. Braking on taxiways was reported as poor by the Tower. I took control of the aircraft at approximately 50 KTS and slowed to taxi speed. We departed the runway on Taxiway A7. There was a slight mound of snow at the entrance to the taxiway otherwise the taxiway looked uniformly covered with snow approximately 1-2 inches thick. I tested the braking action when we were straight on A7; slowed again to turning speed of approximately 7-8 KTS in preparation for turn on to Taxiway A. About 3/4 of the way through the turn I felt the nose wheel skid; and shortly after that felt a shudder. Initially I believed the main wheel had encountered the deeper snow that lined the edge of the taxiway so I straightened the tiller and increased the power to approximately 40%. The aircraft did not move; so I reduced power and we called the Tower for assistance. Additionally; we contacted Company Ramp Operations and Maintenance. When Maintenance arrived at the aircraft they directed us to shut down. Maintenance coordinated for the aircraft to be unloaded on Taxiway A; and brought crew stairs so we could depart the aircraft. Aircraft was later towed to the ramp with no apparent damage. Provide more resources to local agencies for plowing/treating taxiways.


Second narrative: After I performed the landing on Runway 31 at RST control of the aircraft was transferred to the Captain around 50 KTS. The airplane was slowed to a safe speed and turned off the runway onto Taxiway A7. At the time the taxiway had an area of snow left by a snowplow between the runway and the taxiway and about 1 to 2 inches of snow on the taxiway. ATIS reported braking action on the taxiways and ramps as poor. After clearing the runway I began performing my flow for the After Landing Checklist. I had just finished resetting the trim and looked up to monitor our taxi progress and saw we were turning onto Taxiway A. As the airplane was turning it made a slight shudder and came to a stop. The Captain added power to attempt to keep the taxi progressing; but the aircraft wouldn't move. We tried to figure out why it wouldn't move and it looked like the right main gear may have become stuck in snow or slid off the taxiway. We notified Ground Control and they had an airport vehicle conform the right gear was off the pavement. The aircraft was shutdown and unloaded on the taxiway; we were informed it was moved and there was no damage to the aircraft.As the pilot not flying during this phase of flight I should have delayed the after landing flow due to adverse conditions to monitor the Captain and back him up. Once safely clear of any difficult maneuvering I then could have completed the necessary checklist.


Synopsis: Air Carrier flight crew experiences a taxiway excursion during a turn from A7 to A; with the right main gear departing the taxiway. The taxiways were covered with snow and ice and the braking action was reported as poor.