Date: 201903
Local time of day: 1201-1800
Location: ZZZ.Airport, US
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Super King Air 300
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
Reporter organization: Corporate
Reporter function: First Officer; Pilot Not Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP)
Second reporter function: Pilot Flying; Captain
Anomaly: Deviation - Speed All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Ground Event / Encounter Loss Of Aircraft Control; Ground Excursion Taxiway; Inflight Event / Encounter Weather / Turbulence
Detector: Person Flight Crew
When detected: Taxi
Result: Flight Crew Regained Aircraft Control
Contributing factors: Human Factors; Weather
Primary problem: Human Factors

Narrative: We were landing on a visual approach to Runway XX at ZZZ. We were configured early and the approach was stable. The ATIS winds were reported 240/9 variable between 190/260. We observe the winds to be right to left; straight across the runway. We had planned to turn off on Taxiway G; approximately halfway down the runway; as we had done numerous times before. We touchdown and the Pilot Flying entered full reverse. As we began to exit the runway and enter Taxiway G; which is an approximate 45 degree turn to the left; the Pilot Flying brought the throttles to ground fine. However; the turn never stopped. The aircraft continued to turn to the left while the Pilot Flying applied maximum right rudder and braking. The aircraft did not respond. When it became apparent that we were going to leave the taxiway; the Pilot Flying shut down both engines and feathered the props. The left main and the nosewheel exited the taxiway as the left main sank into the mud.A contributing factor may have been the wind. As we turned onto golf the full force of the wind was on the back of the right prop disk while the left disk was shielded by the fuselage. This may have exacerbated the left turn.When we exited the aircraft; we noticed that there were no skid marks on the pavement and no flat spots on the right tires. With maximum braking; we expected to find some evidence of that. We will continue to work with our maintenance department to see if there was a contributing mechanical issue.Because golf is a 45 degree turn from the runway; there is a tendency to take it in a slightly higher speed than a normal taxi speed. I would recommend in the future that you bring the airplane to a taxi speed prior to exiting the runway.


Second narrative: After landing on Runway XX; I made a left turn onto Taxiway G. Right before crossing the hold short the aircraft made an uncommanded left turn into the snow.Even though I had the brakes fully depressed; we did not come to a rapid stop. In fact the tires were not popped or even flat spotted.In my approach briefing I briefed that I would exit taxiway G. There was no need for me to exit at G. I still had half the runway remaining. I believe I took the 45 degree turn off on G at a speed higher than I normally would. That combined with the crosswind we experienced on landing turning into a tailwind most likely produced the left turn.I had the brakes depressed to the floor and the right rudder shoved all the way to the physical stop but the aircraft continued to roll. When I realized we were going to depart the taxiway; I shut the engines off and feathered the props. The left prop contacted the snow. I believe I got complacent with my speed; because I knew the antiskid system was there; but when I needed full braking; the system did not perform in the way I was expecting. In the future; I will not brief that I will get off on a particular taxiway and I will make sure to come to a taxi speed before exiting the runway.


Synopsis: King Air flight crew reported a taxiway excursion after exiting the runway with excess speed.