AN ACR MLG CREW RAN OFF THE SIDE OF THE RWY AFTER A BRAKE FAILURE.

Narrative

IN SUM: AN ACR MLG CREW HAD A FAILURE OF THEIR 'BRAKES AND STEERING CTL UNIT' AFTER TOUCHDOWN ON RWY 21C AT DTW. THE ALTERNATE SYS WAS SELECTED; AND IT; TOO; FAILED LEAVING ONLY L 'NORMAL HYD' BRAKING AND NO NOSEWHEEL STEERING. BRAKING AND DIFFERENTIAL REVERSE ALMOST STOPPED THE ACFT ON THE RWY; BUT IT WENT OFF THE L SIDE AND ENDED UP AXLE DEEP IN SOFT GRASS. PAX AND CREW WERE EVACED DOWNSTAIRS INTO A BUS. THERE WERE NO INJURIES OR DAMAGE TO THE ACFT. THE RPTING CAPT FEELS THAT HE DID ALL THAT HE COULD TO KEEP THE ACFT ON THE RWY; TO DEPART THE RWY AS SLOWLY AS POSSIBLE; AND TO MINIMIZE ACFT DAMAGE AND PAX INJURY. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THIS ACFT TYPE HAS HAD A LOT OF PROBS WITH THE 'BRAKE AND STEERING CTL UNIT.' THE FACTORY HAS REPLACED THE SOFTWARE SEVERAL TIMES AND ANOTHER CHANGE IS ANTICIPATED FOLLOWING THIS INCIDENT. THERE WERE NO OTHER PROBS BESIDES THE BSCU. THE EMER EQUIP WAS SCRAMBLED BEFORE THE ACFT LEFT THE RWY AND WERE AT THE SITE WITHIN SECONDS. THE PAX WERE DEPLANED INTO BUSES WITHIN 40 MINS; A LONG TIME EXCEPT FOR THE FACT THAT THE EMER WAS PAST. THE RPTING CAPT HAD TO TAKE A CHK RIDE WITH THE FAA. THE FAA INSPECTOR WAS NOT VERY HAPPY WITH THE INFO AVAILABLE TO THE LINE PLTS; IN THAT NO LINE PLT KNEW BEFORE THIS INCIDENT THAT THE PARKING BRAKES CAN BE SET WHILE MOVING TO ACTIVATE ANOTHER SET OF VALVES AND STOP THE ACFT.