As reported to the FAA. Reports are unverified, and codes are left as the FAA publishes them.
What was found
DURING CLIMB OF FLIGHT TA588, THE PILOT REPORTED FCU ALTITUDE UNABLE TO CHANGE ALTITUDES. DUE THAT SITUATION THE ACFT RETURNED. AFTER AN UNEVENTFUL LANDING, ONCE THE ACFT PARKED AT THE GATE, PERFORMED FAULT ANALYSIS IAW TSM 22-81-00-810-801-A. REPLACED THE FCU IAW AMM 22-81-12-000-001 & 22-81-12-400-001. PERFORMED TEST IAW AMM 22-96-00-710-001-A WITH NORMAL RESULTS. THE ACFT WAS RETURNED TO SERVICE.