AN ACR B737-500 TAXIES OFF THE HARD SURFACE WHILE ATTEMPTING TO FOLLOW ITS TAXI RTE TO THE RWY. NEWLY FALLEN SNOW COVERING RAMP AND TXWY MARKINGS; AN ABSENCE OF VISIBLE RAMP EDGE MARKINGS AND REDUCED VISIBILITY DUE TO LIGHT SNOW FALLING AND BLOWING THROUGH THE OVERHEAD RAMP LIGHTING SYS WERE FACTORS.

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AT NIGHT; WITH A SNOW COVERED RAMP; WE LEFT THE GATE AREA AND PARALLELED THE RAMP; HDG NE. BASED ON THE AIRFIELD DIAGRAM; WE BELIEVED THERE WAS A TXWY IN FRONT OF US. THERE WAS A BERM OF SNOW FROM SNOW PLOW OPS TO OUR L. PARKED DC10 ACFT (IN STORAGE) WERE TO OUR R. THE SNOW PLOWED AREA ABRUPTLY GOT NARROWER. I ATTEMPTED TO CORRECT TO THE L TO CORRECT TO THE BERM; HOWEVER WE HAD LEFT THE RAMP SURFACE. WHAT WE BELIEVED WAS A TXWY; TURNED OUT TO BE A SVC ROAD. AMA OPS PERSONNEL ADVISED THAT 'NUMEROUS' OTHER CREWS HAVE MADE THE SAME MISTAKE; BUT BECAUSE THE RAMP WAS NOT SNOW COVERED; THEY WERE ABLE TO SEE THEIR ERROR AND MAKE A U-TURN BACK TO TXWY C. CONTRIBUTING CAUSES: 1) SNOW COVERED RAMP; DARKNESS. 2) TXWYS AND SVC ROADS LOOK THE SAME ON THE AIRFIELD DIAGRAM. 3) THERE WERE NO TXWY LIGHTS AT THE EDGE OF THE RAMP. 4) CREW WAS ACCOMPLISHING A CHKLIST AND NOT DEVOTING 100 PERCENT ATTN TO TAXIING. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR WAS TAXIING A B737-500 AND WAS ATTEMPTING TO FOLLOW THE PROPER TAXI RTE ALONG THE RAMP EDGE BY PARALLELING A BERM OF SNOW LEFT BY PLOWS THAT HAD CLRED THE RAMP SOMETIME EARLIER. THERE WERE NO RAMP EDGE LIGHTS VISIBLE AND THE FLC COULD NOT SEE THE TAXI LINES WHICH WERE COVERED BY MORE RECENT SNOWFALL; SOME OF WHICH WAS STILL FALLING AND BLOWING AROUND AND REDUCING VISIBILITY WHEN THE OVERHEAD RAMP AREA LIGHTS REFLECTED OFF IT. HE COULD JUST SEE THE TAXI LIGHTS OF TXWY C UP AHEAD AND THOUGHT THAT HE WAS ON THE PROPER RTE TO THAT TXWY WHEN HE FELT THE ACFT SLOW ABRUPTLY. THE AMA ARPT PERSONNEL WHO HELPED THE PAX LEAVE THE ACFT SAID THAT THIS HAS HAPPENED SEVERAL TIMES; THE CAPT ALLEGED. THE PREVIOUS ACFT WERE; FOR THE MOST PART; ABLE TO TURN AROUND OR BE PUSHED OUT OF THIS TRIANGULAR AREA. THE ACFT WAS FINALLY REMOVED BY A COMPANY RECOVERY TEAM USING 2 SNOW PLOWS AND LARGE CABLES AROUND THE MAIN GEAR STRUTS. THERE WAS NO DAMAGE TO THE ACFT OR THE ARPT PROPERTY; ACCORDING TO THE RPTR.