What was found
DURING TAXI OUT WE RECEIVED A VENTRAL RUDDER FAIL CAS FOLLOWED BY AP FAIL AND YD FAIL. WHEN WE STOPPED TAXIING, ALL MESSAGES DISAPPEARED. WHEN WE STARTED TO TAXI AGAIN, THEY IMMEDIATELY CAME BACK. CORRECTIVE ACTION: POWERED ON AND NO CAS MESSAGE PRESENTED. PERFORMED SUCCESSFUL OPS CHECK OF RUDDER WITH NO ISSUES. DOWNLOADED ARES DATA AND SENT, TEXTRON CAME BACK WITH THE MESSAGE POSTED DUE TO STANDBY RUDDER RESERVOIR SYSTEM LOW. VERIFIED THE RESERVOIR WAS LOW AND SERVICED, THEN RESTORED AIRCRAFT TO ORIGINAL CONFIGURATION. WORK PERFORMED IAW AMM 12 10 47.