Small Transport; Low Wing; 2 Turboprop Eng
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 60; Flight Crew Total 2890; Flight Crew Type 180
Situational Awareness; Distraction; Confusion
Deviation / Discrepancy - Procedural Other / Unknown
Flight Crew Became Reoriented; Flight Crew Took Evasive Action
Airport; Chart Or Publication; Procedure
[I] landed in IFR conditions low visibility at an unfamiliar airport; ACV. Landed after ILS Runway 32. [I] taxied back and went on the red restricted area. I was looking for the FBO and noticed I taxied on [the restricted area] so I turned off of it then stopped to look at where I needed to go to drop the 2 passengers off. Then a passenger got out so I told him to wait we were not in the right spot so he got back in and I taxied to the right area. It was a restricted area for airline flights only at an un-towered field and no airlines were there so I didn't notice with the low visibility until I was in the red area. But as soon as I saw it I went out. [I] probably taxied 20 feet into it. The airport diagram on the charts didn't show the restricted area so that would be helpful. I printed out an airport diagram also but it just showed taxiways and runway not the restricted area either. The Airport FD did say there was an airline service working out of there so I should have paid more attention to that but still never mentioned a restricted area. I could maybe look in the flight guide that would have showed me the exact spot to go for the FBO instead of looking out in low visibility trying to see it.
After landing at ACV in low visibility; the pilot taxied into the ramp area reserved for air carrier aircraft before realizing where he was. There are no publications or charts indicating the red hash mark area restrictions.