EXCURSION FROM TXWY.

Narrative

DURING TAXI TO RAMP AFTER LNDG; GND CTL 121.4 WAS ADVISED BY ME THAT WE WERE IN A RENTAL ACFT UNFAMILIAR WITH THE ARPT AND REQUESTED PROGRESSIVE TAXI DIRECTIONS TO RAMP. GND CTL GUIDED US TO TXWY M BESIDE THE RAMP AT WHICH TIME MAINT PERSONNEL USED HAND SIGNALS FROM THE RAMP INDICATING WE SHOULD TAXI AROUND TO THE SW CORNER ENTRANCE. THIS ENTRANCE CAN BE SEEN COMING FROM RWY 9R/TXWY L ON THE ATTACHED ARPT DIAGRAM. WE ADVISED GND CTL OF OUR REQUIREMENT TO CONTINUE TAXI FROM TXWY M OUT TXWY H; UP TXWY L; WBOUND IN ORDER TO ENTER RAMP. GND CTL ASKED IF WE COULD MAKE THE TURN FROM TXWY H ONTO TXWY L WHICH I ADVISED YES WE COULD. AS WE MADE THE TURN THE R MAIN GEAR CAME ABOUT 5 FT OFF THE TXWY INTO THE MUD. ACFT MOVEMENT STOPPED AND WE SHUT DOWN ALL ENGS TO PREVENT FOD DAMAGE. THE NOAA 'ARPT FACILITY DIRECTORY' DOES ADVISE THE TXWYS ARE 50 FT WIDE OR LESS BUT NOTHING IS STATED THAT THESE TXWYS ARE UNUSABLE BY LARGE ACFT (OVER 12500 LBS). ALSO; BEING UNFAMILIAR WITH THE ARPT AS WE ADVISED; GND CTL SHOULD HAVE ADVISED US OF A BETTER TAXI RTE -- SUCH AS UTILIZE RWY 9R AND NOT TXWY L. WE WERE THE 4TH LARGE ACFT IN RECENT MONTHS AND THE SECOND LARGE ACFT IN 2 WKS TO TURN SHORT ON KFLL TXWYS. KFLL ARPT (RWY 9L AND RAMP AREA) HAS BEEN UPGRADED TO HANDLE JET ACFT BUT ALL TXWYS HAVE NOT BEEN UPGRADED WHICH CREATES CONFUSION AND PROBS. SMALL NON-UPGRADED TXWYS SHOULD BE NOTAMED AS NON- USABLE FOR LARGE ACFT AND GND CTL/ATIS SHOULD ADVISE FLCS.