Date: 201701
Local time of day: 0601-1200
Location: RNO.Airport, NV
Flight conditions: IMC
Weather elements / visibility: Snow; 5
Light: Night
Aircraft: Small Transport; Low Wing; 2 Turbojet Eng
Operator: Corporate
Operating under: Part 91
Flight plan: IFR
Mission: Passenger
Flight phase: Taxi
ATC / advisory: Ground RNO
Reporter organization: Corporate
Reporter function: Single Pilot; Pilot Flying
Reporter qualification: Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor; Flight Crew Instrument
Human factors: Confusion; Workload; Fatigue; Situational Awareness
Anomaly: Ground Excursion Taxiway
Detector: Person Flight Crew
When detected: Taxi
Result: Air Traffic Control Provided Assistance; Flight Crew Requested ATC Assistance / Clarification; Flight Crew Returned To Gate; General Flight Cancelled / Delayed
Contributing factors: Airport; Weather; Human Factors
Primary problem: Ambiguous

Narrative: My passengers were boarded and I started engines at approximately XD:45. I completed all after start checklist and programming items before taxiing as is SOP in a single-pilot jet. It was snowing very lightly so I turned on the windshield heat to aid exterior vision. My taxi clearance was from the FBO to runway 16R via Charlie. Due to cloud cover and the early hour; it was still very dark. The ramp and taxiway markings were covered with a thin layer of snow. On the G1000 MFD I brought up the taxi diagram of the airport. I observed there was a non-paved area separating the ramp from the taxiway. My plan was to exit the ramp westbound on the connector; then the next right turn would be taxiway C. As I exited the ramp I was trying to discern from the blue taxiway lights ahead exactly when I was going to intersect Charlie. I thought the dark area to my right was part of the ramp when it was really the unpaved area between the ramp and Charlie. As I continued westbound on the connector; I thought the white area to my right was the unpaved area when in fact I was crossing Charlie. I saw a break in the blue lights straight ahead and assumed that was the end of the connector and entrance to Charlie. Due to the darkness; I assumed the dark surface past the blue lights was the groomed taxiway. It was not and now I was taxiing into the gravel. I didn't know what kind of surface I was on so I tried to turn around but couldn't in the soft material. I informed Ground Control that I believed I had overshot taxiway C. I then shut the plane down. I called the FBO for assistance and the passengers were taken back there. The FBO brought a tug and with assistance from Airport Operations pulled the plane back to the ramp. There was no damage to the plane or airport equipment or structures.Here are my thoughts on this humbling event:1. Fatigue may have been a contributing factor. I received a text from one of my passengers at XA:00 informing me they would arrive at about XD:30. I had trouble falling back to sleep and finally got up at XB:00 with about 5 hours of sleep.2. I'm not very familiar with this area of the airport. I had only used this ramp once prior and that was during daylight with much better weather.3. Difficult outside vision through a windshield covered with droplets combined with a mediocre taxi light. These were red flags calling out for extra vigilance.4. Negative transference. When driving a car; the road is usually the dark area and the snow-covered areas are dirt; grass; and other non-paved places. Today's visual cues were the opposite. The G1000 Safe Taxi is a wonderful tool; but you mostly look out the windshield while taxiing. That subjects us to errors of interpretation.5. The biggest contributing factor was the lack of signage combined with the confusing break in the taxiway lights at my 12 o'clock when exiting the ramp. If there were blue lights in front of me; I would have stopped to question my navigating skills. Instead there were two dim reflectors spaced on either side of me that I wrongly assumed marked the connector's intersection with Charlie. The reflectors aren't helpful. I feel they contributed to the error. There are no taxiway signs at that ramp exit and yellow lines don't help when they can't be seen.




Synopsis: Pilot reported a taxiway excursion during night operations in degraded weather conditions. Single pilot operations; poor taxiway signage; and fatigue all reportedly contributed to the event. The aircraft was towed from the unprepared surface with no damage noted.