As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
AIRCRAFT NOT GROUNDED. AUTOPILOT MADE AN UNCOMMANDED DESCENT IN VERTICAL NAVIGATION PATH FL380, NEGATIVE TURBULENCE, CENTER AUTOPILOT ENGAGED IN COMMAND DESCENT STOPPED WHEN ALTITUDE HOLD SELECTED. REMOVED AND REPLACED FLIGHT CONTROL COMPUTER IAW AMM 22-11-01. OPERATIONAL CHECK GOOD. (CLOSED)