BAE PROVOST TRAINING JET HAS DIFFERENTIAL BRAKING MALFUNCTION AND EXITS TXWY CAUSING SOME ACFT AND SIGNAGE DAMAGE PRIOR TO COMING TO A STOP.

Narrative

ABOUT XA45; I PREFLTED THE ACFT FOR A LCL PLEASURE FLT. AFTER CHKING THE WX AND LISTENING TO THE LCL ATIS; I WAS CLRED FROM GND CTL TO TAXI TO RWY 31. PART OF THE NORMAL CHKLIST PROC IS TO CHK YOUR BRAKES BY INDICATION OF A PRESSURE GAUGE LOCATED IN THE COCKPIT AND BY TAPPING THE BRAKES IMMEDIATELY AFTER THE ACFT STARTS MOVING FOR PROPER RESPONSE. ALL INDICATIONS WERE NORMAL; AND I PROCEEDED TO TAXI TO RWY 31 AS CLRED. THIS TYPE OF ACFT USES DIFFERENTIAL BRAKING TO STEER THE ACFT ON THE GND. AT THIS TIME; THE WINDS ARE CALLED AT 330 DEGS AND 24 KTS. HVY BRAKING IS REQUIRED TO KEEP THE ACFT AT A NORMAL TAXIING SPD DUE TO A STRONG TAILWIND. ALL INDICATIONS ARE NORMAL UNTIL I PROCEEDED TO STOP STRAIGHT AHEAD BY TAPPING BOTH BRAKES SIMULTANEOUSLY. AT THIS TIME; THE ACFT STARTED TO TURN TO THE L DUE TO THE R BRAKE NOT ENGAGING. IMMEDIATELY; I PROCEEDED TO SHUT DOWN THE ENG TO STOP THE ACFT FROM MOVING FURTHER. THE ACFT WENT INTO THE GRASS AREA; NOT TO THE TXWY; AND BEFORE IT CAME TO A COMPLETED STOP; COLLIDED WITH A TXWY SIGN. I PROCEEDED TO SECURE THE ACFT AND TO EXIT THE ACFT. DAMAGE TO BOTH THE ACFT AND THE TXWY SIGN WERE VERY MINIMAL AND ONLY REQUIRE LIGHT TOUCH-UP ON THE LEADING EDGE OF THE WING. NO OTHER DAMAGE TO PROPERTY OR CREW WERE NOTED. I FEEL CONTRIBUTING FACTORS ARE: LOW TEMP AT THE TIME OF INCIDENT; CAUSING BRAKE TO MALFUNCTION DUE TO DRY SEALS; AIR IN THE LINES OR MECHANICAL FAILURE OF R BRAKES.