As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
PHL - FLT 98 - AT FL330, WITH CENTER COMMAND SELECTED, THE AUTOPILOT DISCONNECTED WITH THE ASSOCIATED LIGHTS AND WARNING. A STRONG ACRID SMELL WAS NOTED COMING FROM THE MODE CONTROL PANEL (MCP). THE AUTOPILOT WAS SWITCHED. FLIGHT RETURNED TO PHL AND LANDED WITHOUT FURTHER INCIDENT. MAINTENANCE REPLACED THE MCP AND THE FLIGHT CONTROL COMPUTER. (M)