B747-200 CAPT REPORTS APPARENT AUTOPILOT FAILURES THAT CAUSED HIM TO HAND FLY CAT II ILS ALTHOUGH ACTUAL VISIBILITY IS ABOVE CAT I MINIMUMS.

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APCH ADVISED TO HOLD W OF ZZZZ2. AUTOPLT A WAS BEING USED; AUTOPLT B WAS MEL'ED DUE TO UNCOMMANDED PITCH AND HDG CHANGES. WHILE ATTEMPTING TO TURN OUTBOUND AUTOPLT A WAS NOT RESPONDING TO HDG INPUTS. AUTOPLT WAS DISCONNECTED; THE ACFT RAPIDLY DSNDED 400 FT BELOW THE ASSIGNED ALT. AFTER RE-TRIMMING AND CLBING BACK TO THE ASSIGNED ALT AUTOPLT A WAS REENGAGED. ON THE INBOUND TURN TO ZZZZ2 AUTOPLT A AGAIN WOULD NOT RESPOND TO HDG INPUTS AND RAPIDLY DSNDED 400 FT BEFORE I COULD DISENGAGE AUTOPLT A. ONCE DISENGAGED THE ACFT WOULD PITCH UP/DOWN +/-1500 FPM. THE ACFT WAS RE-TRIMMED; HOWEVER THE AUTOPLT WAS NOT REENGAGED. AT THIS TIME APCH CLRED US FOR THE ILS. INSIDE THE FAF TWR WAS CONTACTED AND WE WERE CLRED TO LAND. PRIOR TO LNDG AND INSIDE THE OM; TWR ADVISED RVR 1600/1400/1600. THE ENTIRE APCH LIGHT SYS; RWY APCH END LIGHTS REILS AND MARKINGS WERE VISIBLE FROM 10 MI OUT. A NORMAL LNDG WAS MADE. THE FOLLOWING WRITE-UP WAS MADE IN LOGBOOK: A AUTOPLT WOULD NOT HOLD ALT. ACFT DSNDS 400 FT BELOW SELECTED ALT IN EXCESS OF 1500 FPM; THEN CLBS 400 FT ABOVE SELECTED ALT AT 1500 FPM. WHEN AUTOPLT IS DISCONNECTED ACFT DSNDS AT 1500 FPM UNTIL PITCH TRIM CAN BE RE-TRIMMED FOR NORMAL FLT. OTHER WRITE-UPS FOR PITCH AND HDG DEVS WERE RECORDED ON OTHER LOG PAGES. MAINT ALSO REFED BOEING SVC LETTER FOR R ELEVATOR PWR PACKAGE.