As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
WHILE APPLYING THE BRAKES ON TAXI OUT A LOUD BANG WAS HEARD FOLLOWED BY AN ABRUPT LEFT TURN WITH NO ABILITY TO STEER OR BRAKE RIGHT. AIRCRAFT HAS CASTERING NOSE WHEEL. UPON BRAKE REMOVAL THE MOUNTING FLANGE WAS FOUND COMPLETELY SEPARATED FROM THE REST OF THE BRAKE ROTOR. PICTURE AVAILABLE