A CE560 PLT CAUGHT THE ACFT'S L MAIN TIRE IN A SNOW BANK AFTER TURNING OFF A TXWY ONTO AN UNPLOWED VEHICLE ACCESS ROAD.

Narrative

AFTER LNDG FROM AN ILS 1 APCH AT CAK ARPT; AND CLRING THE RWY; GND CTL CLRED US TO TAXI TO FBO LOCATED E OF TWR; PARALLEL TO RWY 5/23. WHILE TAXIING ON THE OUTER TERMINAL TXWY; PLOWING WAS UNDERWAY AND VISIBILITY WAS REDUCED DUE TO CONTINUOUS SNOW FALL. THE FO WAS COPYING OUR ATC CLRNC TO PITTSBURGH AND I WAS TAXIING IN TO THE FBO. FROM THE MAIN TERMINAL RAMP AND WHERE THE PARALLEL TXWY BREAKS OFF FOR RWY 5/23 THERE IS ALSO AN ACCESS ROAD THAT LOOKS LIKE A TXWY AND IS UNCLRLY MARKED THAT GOES IN TO THE RAMP AREA OF THE FBO AND OTHER CORPORATE HANGARS. I COULD NOT CLRLY MAKE OUT THE DOGLEG. I SAW A FUEL TRUCK AND SNOW PLOW MOVING TO MY R ON WHAT SEEMED TO BE THE TXWY LEADING IN TO THE RAMP AREA OF THE FBO; SO I TURNED AND GOT MY L TIRE CAUGHT IN A SNOW DRIFT THAT WAS OFF THE ACCESS ROAD/TXWY BY 2-3 FT. WE SHUT DOWN AND REQUESTED THE FBO COME OUT AND HELP TOW US BACK ONTO THE TXWY. NO DAMAGE OCCURRED TO THE ACFT. DUE TO THE REDUCED INCLEMENT WX CONDITIONS; THE FACT THAT IT WAS STILL NIGHT OPS AND MY UNFAMILIARITY WITH THE ARPT I SHOULD HAVE INSISTED ON PROGRESSIVE TAXI INSTRUCTION. FURTHERMORE; I WOULD RECOMMEND THAT BETTER SIGNAGE AND/OR LIGHTING BE CONSIDERED FOR THAT AREA. IT IS VERY DIFFICULT TO DISTINGUISH BTWN THE RAMP; TXWY; AND RAMP AREAS AND I UNDERSTAND THAT THEY HAVE HAD SIMILAR OCCURRENCES TAKE PLACE (1-3 PER MONTH).