C500. ACFT BRAKES FAILED RESULTED IN ACFT DEPARTING TXWY.

Narrative

DURING TAXI; BRAKES FAILED IN BOTH ANTI-SKID PWR AND MANUAL POS. ACFT EXITED TXWY TO L SIDE. ACFT WAS CTLED BY USE OF L THROTTLE TO TURN ACFT DURING EXCURSION OFF OF RWY. EXTREMELY MINOR DAMAGE WAS DONE TO UNDERSIDE OF ACFT WING AND FLAP. AIRFRAME IS UNDERGOING REPAIRS TO WING AND FLAP. BRAKES ARE BEING EVALUATED THIS TIME. THE ANTI-SKID ADD ON; IS APPROVED AND SUPPLIED BY A COMPANY BY THE NAME OF 'CRANE.' I QUESTION IF THIS STYLE OF BRAKES SHOULD BE USED ON OTHER ACFT OF THIS TYPE. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE ACFT; A CESSNA CITATION 500 HAS NO NOSEWHEEL STEERING. AT TAXI SPD THE ONLY DIRECTIONAL CTL THE ACFT HAS IS DIFFERENTIAL BRAKES. WHEN TOTAL BRAKE FAILURE OCCURRED THE ACFT HAD NO DIRECTIONAL CTL. THE ACFT WAS MODIFIED WITH AN AFTER MARKET STC ACFT BRAKE ANTI-SKID SYS. THIS SYS UTILIZES A HYD SHUTTLE VALVE TO DIRECT SYS PRESSURE FROM EITHER THE ANTI-SKID SYS OR THE NORMAL BRAKE SYS. IF THIS SHUTTLE VALVE FAILS IN AN INTERMEDIATE POS; BOTH SYS ARE PORTED TO RETURN; THUS TRIGGERING A COMPLETE BRAKE SYS FAILURE. THE AFTER MARKET VENDOR IS 'CRANE;' AND THE STC NUMBER IS SA 2025 WE. THE PLT IS CONCERNED THAT THIS MODIFICATION MAY ALSO BE RETROFITTED ON TO OTHER ACFT OF THIS TYPE AND THAT THEY COULD HAVE THE SAME PROB. CRANE MAY HAVE GONE OUT OF BUSINESS. THE STC IS NOW OWNED BY 'HYDRAULICS UNLIMITED.'