As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
(CAN) ACFT DID AN IN-FLIGHT TURNBACK DUE TO FLT ALT WINDOW STUCK AT 5000 FT. MAINTENANCE TROUBLESHOT AND FOUND THE MODE CONTROL PANEL TO BE AT FAULT. MCP WAS REPLACED AND SYSTEM TESTED SERVICEABLE, WORK DONE IN ACCORDANCE WITH MM 22-11-34