FA10 EXITS TXWY WHEN ANTI-SKID SYSTEM FAILS AND ACFT CANNOT BE SLOWED ADEQUATELY FOR A TURN AT FXE.

Narrative

WE LANDED AT FXE WITHOUT ANY ABNORMALITIES. ALL BRAKING; ANTISKID; AND LNDG SYS FUNCTIONED NORMALLY. AFTER VACATING THE RWY AT A RELATIVELY SLOW SPD; WE MADE A 90 DEG R TURN TO EXIT THE RWY CLR ZONE. IN OUR TURN; THE ACFT LOST ALL NORMAL BRAKING ABILITIES AND ACTUALLY BEGAN TO MOVE FASTER. OUR ACFT STEERING SYS WAS WORKING PROPERLY; BUT IN ORDER TO MAKE SUCH 'SHARP' TURNS; SOME DIFFERENTIAL BRAKING IS NEEDED. WE HAD NONE. THE ACFT WAS PROCEEDING TOWARDS A TXWY SIGN AND I HAD TO USE THE EMER BRAKE. HOWEVER; WE WERE ON SUCH A SMALL TXWY AND POSITIONED CLOSE ENOUGH TO THE TXWY SIGN; I HAD TO ACTUALLY TURN BACK TO THE L TO AVOID THE SIGN. IN DOING SO; WE WERE FORCED OFF THE TXWY INTO THE GRASS BEFORE COMING TO A SLIDING STOP. OUR ACFT HAD NO SERIOUS DAMAGE. THE R OUTBOARD SLAT HAD A SMALL DENT FROM HITTING A TXWY LIGHT; BUT NO DAMAGE TO ANY OF ITS INTERNAL PARTS. UPON OUR MAINT DEPT'S EXAM THE FOLLOWING DAY; IT WAS FOUND THAT AN ANTISKID COMPUTER HAD FAILED. THEY HAD JUST PREVIOUSLY INSTALLED THIS UNIT AND FOUND AFTER FURTHER REVIEW THAT IT HAD OBVIOUSLY 'GONE BAD' WHEN WE WERE IN OUR TURN. THE UNIT XMITTED TO OUR BRAKE SYS A SKID SITUATION; SO IT RELEASED ALL BRAKING AUTH. IT WAS FOUND THAT WITH THE ANTISKID SYS OFF; ONE WOULD HAVE BRAKES. HOWEVER; I HAD BUT MAYBE 1 SECOND TO REACT TO THE SITUATION; LEAVING NO TIME TO LOOK DOWN AND TURN OFF THE ANTISKID SYS WITH THE HOPES THAT BRAKING ABILITY WOULD RETURN. I HAVE NEVER HAD TO USE ANY KIND OF EMER BRAKE SYS; OTHER THAN FOR TRAINING SITUATIONS. IT IS MY OPINION THAT WITHOUT THIS SYS OUR ACFT WOULD HAVE HAD MUCH MORE DAMAGE AS WOULD THE ARPT ENVIRONMENT. THE VERY SANDY GRASS AREA JUST OFF THE TXWY WAS DEFINITELY ALSO A FACTOR. I CAN SAY THAT PREVIOUS SIMULATOR TRAINING HELPED ME MAKE A TIMELY REACTION TO A BAD SITUATION.