AN ACR MLG CREW FOUND ITSELF ON A VERY NARROW TXWY AT NIGHT WITH VERY DIFFICULT TURN OFFS.

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AFTER LNDG ON RWY 22 AT LEXINGTON AT XA30 PM ON MAY/WED/93; WE WERE TAXIING INTO THE RAMP ON TXWY A. APCHING THE ACR RAMP; I OBSERVED AN ACR TWIN TURBO-PROP PARKED IN CLOSE PROX TO THE GATE WE HAD BEEN ASSIGNED. FROM OUR POS ON TXWY A; AS WE APCHED THE RAMP IT WAS DIFFICULT TO JUDGE HOW MUCH ROOM LAY BTWN THE TWIN AND THE EDGE OF THE APRON WE WOULD BE TAXIING BTWN IF WE WERE TO ENTER THE RAMP DIRECTLY FROM TXWY A. I CHOSE TO TURN SEBOUND ON TXWY B; AND ENTER THE RAMP FROM TXWY B BEYOND THE LOCATION OF THE TWIN. THERE WERE NO NOTES ON THE ARPT DIAGRAMS THAT WOULD INDICATE THIS TXWY WAS UNSUITABLE FOR ENTRY TO THE RAMP; BUT ONCE ON IT; I REALIZED THAT THE INTXNS LEADING TO THE RAMP FROM IT WERE NOT SUITABLE FOR OUR TYPE OF ACFT MLG. I PASSED UP THE FIRST INTXN TO THE RAMP BECAUSE I DID NOT BELIEVE I COULD NEGOTIATE THE TURN WITHOUT DEPARTING THE TXWY. I CHOSE THE NEXT INTXN TO MAKE A 180 DEG TURN BACK ONTO THE PARALLEL TXWY C AND APCH THE RAMP NWBOUND. THIS INTXN PERMITTED A SLIGHTLY WIDER TURNING RADIUS. THE TURN BACK TO TXWY C WAS COMPLETED WITHOUT PROB; THOUGH IT WAS DETERMINED LATER THAT OUR L GEAR TRUCK DEPARTED THE TXWY SLIGHTLY ABOUT 130 DEGS THROUGH THE TURN. WE PROCEEDED TO THE RAMP VIA TXWY X; AND THEN TO OUR GATE. GIVEN THE TIGHTNESS OF THE TURN BACK TO TXWY C; WE PROCEEDED TO THE WHEEL WELLS TO SEE IF THERE WAS ANY EVIDENCE THAT WE HAD DEPARTED THE TXWY. WHILE THERE WAS NO DAMAGE TO THE GEAR; THERE WAS A THIN STREAK OF DIRT ON THE TIRES CONFIRMING AN EXCURSION. I CERTAINLY WILL NEVER TURN DOWN TXWY B AGAIN; AND HAD IT BEEN DAY TIME; I DO NOT BELIEVE I WOULD HAVE CHOSEN TO DO SO IN THIS INSTANCE; BUT AT NIGHT WITH POOR VISUAL CUES; RAMP CONGESTION; AND NO PUBLISHED RESTRICTIONS PRECLUDING ITS USE BY LARGER ACFT; I BELIEVE TXWY B WILL CONTINUE TO BE A SOURCE OF TXWY EXCURSIONS FOR ACR CREWS UNFAMILIAR WITH THE LEXINGTON ARPT. SUGGESTIONS: A NOTE ON THE ARPT DIAGRAM RESTRICTING THE USE OF TXWYS C AND B TO GROSS WTS 70000 LBS AND LESS. A SIGN SHOWING TXWYS B AND C AS ROUTING TO THE CIVIL AVIATION RAMP. MORE RESTRICTIVE PARKING PROCS THAT REQUIRE ACFT PARKED ON THE ACR RAMP OVERNIGHT; TO BE POSITIONED CLOSER TO THE TERMINAL TO ALLOW GREATER TAXI CLRNCS FOR NIGHT TIME OPS (THE EDGE OF THE APRON IS POORLY LIT AND TRYING TO ASSESS TAXI CLRNCS AT A DISTANCE IS VERY TENUOUS).