As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT WAS GROUNDED: CAT 3 DUAL DISPLAYED IN INOPERATIVE SYSTEM. ATTEMPTED COMPUTER RESET PER QRH WITH NO OTHER FAILURE. WHEN CHANGED FROM AUTOPILOT 2 TO AUTOPILOT 1, AIRCRAFT PITCHED DOWN AND INITIATED UNCOMMANDED DESCENT. STOPPED COMPUTER RESET AS UNSUCCESSFUL. MAINTENANCE REPLACED #1 AIR DATA AND INERTIAL REFERENCE UNIT (ADIRU) AND ACCOMPLISHED A SATISFACTORY OPERATIONAL CHECK PER AMM 34-12-34.