COMMUTER ACFT HAS NOSEWHEEL STEERING PROB. LOSS OF CTL; ENDS UP ON GRASS OFF TXWY.

Narrative

WHILE TAXIING OUT TO RWY 13 IN MCALLEN; THE TILLER NWS BECAME INTERMITTENT. THE ACFT WAS STOPPED ON THE TXWY NEAR THE END OF RWY 13. I HAD NO VISUAL INDICATIONS EXCEPT THAT THE GREEN LIGHT ON THE NWS WOULD GO OFF AND ON. I LOOKED UP THE NWS IN THE MEL BOOK AND IN INTERPRETED IT TO MEAN THAT THE NWS SYS COULD BE MEL'ED. I COMPLIED WITH THE MEL BY ASKING THE FO TO PULL THE CIRCUIT BREAKER; WHICH HE POINTED TO AND ASKED IF THAT WAS THE RIGHT ONE; AND I SAID YES. I MADE AN ENTRY INTO THE LOGBOOK AND CONTINUED THE FLT PER MEL. (THIS WAS MY FIRST MAINT WRITE-UP IN A LOGBOOK AS A NEW CAPT.) IN RETROSPECT; ESPECIALLY IN LIGHT OF THE PROBS WITH THE NWS; I SHOULD HAVE TAXIED BACK IN AND TALKED TO MAINT ABOUT THE PROB; BUT THOUGHT THAT I HAD UNDERSTOOD WHAT WAS REQUIRED. THE TKOF AND FLT WERE ACCOMPLISHED BY THE FO AND WERE NORMAL UNTIL THE GEAR WAS LOWERED ON APCH INTO SAN ANTONIO. WE HAD A NOSE GEAR DOWN LIGHT UNSAFE CONDITION. I CHKED THE LIGHT BULB; WHICH WAS WORKING AND RECYCLED THE GEAR WHICH THAT TIME; GAVE US A NORMAL INDICATION. SAN ANTONIO IS BASICALLY USING ONLY 1 RWY FOR ACR OPS; RWY 21/3. THE WINDS WERE 160 AT 18; AND WE WERE LNDG ON RWY 21. THE FO'S LNDG AND ROLLOUT WERE NORMAL UNTIL HE BEGAN TO TURN TO THE R OFF THE RWY AT TXWY E. THE ACFT SWERVED HARD TO THE R AND COULD NOT BE STOPPED WITH MAX BRAKING AND REVERSE PWR BEING APPLIED. THE ACFT CAME TO A STOP WITH THE NOSE GEAR APPEARING TO BE OFF THE TXWY AND POSSIBLY IN THE GRASS. THE TWR CALLED AND SAID THEY HAD AN ACFT ON FINAL AND WERE WE CLR OF THE HOLD LINE ON THE TXWY. I REPLIED THAT WE WERE NOT AND THEY ASKED IF WE WOULD BE ABLE TO CLR. I SAID THAT I WOULD TRY. KNOWING THAT THE ARPT WAS DOWN TO A SINGLE RWY OPS AND THERE WERE ACFT ON FINAL; I FELT PRESSURE TO MAKE AN ATTEMPT TO FREE THE ACFT WHILE ALSO TAKING INTO ACCOUNT THE CLRNCS AND STABILITY OF THE ACFT'S POS. I MADE A BRIEF ATTEMPT TO MOVE THE ACFT BACK ONTO THE TXWY BY USING REVERSE. I DID THIS ONLY MOMENTARILY AND IT DID NOT MOVE THE ACFT. THEN WHEN THE TWR ASKED AGAIN IF WE WOULD BE ABLE TO CLR; I ATTEMPTED TO MOVE FORWARD TO BE ABLE TO TURN L BACK ONTO THE TXWY; BUT THE L MAIN STOPPED IN SOFT DIRT AND THE ATTEMPT WAS ABANDONED. I NOTIFIED THE TWR AND SAT OPS AND SHUT DOWN THE ENGS. I KNOW THAT IT WAS A MISTAKE TO ATTEMPT TO MOVE THE ACFT; BUT I THINK THAT IT WAS THE STRESS OF THE SIT AND THE PRESSURE THAT I FELT FROM THE TWR; TO AT LEAST MAKE AN ATTEMPT TO CLR THE RWY FOR NOT SHUT DOWN THE ARPT IF I COULD DO SO WITHOUT ENDANGERING ANYONE OR CAUSING ANY DAMAGE TO THE ACFT.