As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING TAXI OUT OF FLIGHT 8126 THE COPILOTS LEFT BRAKE WAS INOPERATIVE, THE BRAKE WENT TO THE FLOOR. AFTER TROUBLESHOOTING THE MECHANIC FOUND A BAD BRAKE MASTER CYLINDER. THE MASTER CYLINDER WAS REPLACED IAW ATR72 MM JIC 32-42-13-RAI-10000. THE SYSTEM CHECKED GOOD AND THE AIRCRAFT WAS RETURN TO SERVICE.