Narrative:

Reported WX conditions required a CAT 3 approach and automatic land. On center autoplt intercepted localizer and glidepath to ZZZZ runway 17L. At approximately 2800 ft above the runway aircraft center autoplt aggressively pitched the aircraft nose down then up at which time the autoplt disconnected with warning. I engaged the right autoplt and the localizer and GS intercepted indicated captured for a moment. The aircraft pitched down more aggressively than the first time then up very rapidly. At the same time the first officer stated his localizer and GS capture modes on his ADI/pdi both had red lines through them. I engaged the left autoplt. The localizer and GS indications were captured; still in the slot on speed as I continued to fly and configure aircraft through the malfunctions. The left autoplt seemed just fine. My localizer and GS indications remained normal; captured when connected to left autoplt. The first officer questioned tower regarding runway 17L visibility; we could not see the runway. Tower controller responded with runway visibility that required an aircraft CAT 3 automatic land operation. At 1700 ft AGL; I reengaged center and right autoplt. At 1400 ft AGL; aircraft completed its own test and indicated land 3. The first officer's flight instrument indications were now normal localizer and GS captured. For a moment; everything was copasetic. As we descended through 700 ft AGL the aircraft asa downgraded equivalent to CAT 1 status; so I completed a normal missed approach; go around procedure. Even directly overhead; I did not visually acquire any portion of runway 17L. On top of the fog bank blanketing the runway; it was a beautiful day in ZZZZ. That's all the half english speaking passenger would remember. ZZZZ operations told our flight attendants and customers that there was no reason for us to go around; the visibility over their desk tops was perfect. Our current aircraft and runway status; coupled with aircraft arriving ZZZZ from all directions; I elected to divert to ZZZZ1. It was difficult working/communicating with the air traffic controllers on this particular flight/day; my experience told me that after making it around the pattern in the valley could put us well behind the fuel curve to safely divert to ZZZZ1. Additionally; crew fatigue was also possibly a factor. Once safely on the ground in ZZZZ1; we learned that aircraft history included many problems with the center and right autoplts over a period of time covering 54 legs of flying. In the past; all autoplt faults on this aircraft; as per the maintenance log were successfully reset on the ground.

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Original NASA ASRS Text

Title: A B767 EXECUTED A GAR ON A CAT III APCH AFTER THE ACFT EQUIPMENT CAPABILITY DOWNGRADED TO CAT 1. THE FLT DIVERTED TO AN ALTERNATE.

Narrative: RPTED WX CONDITIONS REQUIRED A CAT 3 APCH AND AUTO LAND. ON CTR AUTOPLT INTERCEPTED LOC AND GLIDEPATH TO ZZZZ RWY 17L. AT APPROX 2800 FT ABOVE THE RWY ACFT CTR AUTOPLT AGGRESSIVELY PITCHED THE ACFT NOSE DOWN THEN UP AT WHICH TIME THE AUTOPLT DISCONNECTED WITH WARNING. I ENGAGED THE R AUTOPLT AND THE LOC AND GS INTERCEPTED INDICATED CAPTURED FOR A MOMENT. THE ACFT PITCHED DOWN MORE AGGRESSIVELY THAN THE FIRST TIME THEN UP VERY RAPIDLY. AT THE SAME TIME THE FO STATED HIS LOC AND GS CAPTURE MODES ON HIS ADI/PDI BOTH HAD RED LINES THROUGH THEM. I ENGAGED THE L AUTOPLT. THE LOC AND GS INDICATIONS WERE CAPTURED; STILL IN THE SLOT ON SPD AS I CONTINUED TO FLY AND CONFIGURE ACFT THROUGH THE MALFUNCTIONS. THE L AUTOPLT SEEMED JUST FINE. MY LOC AND GS INDICATIONS REMAINED NORMAL; CAPTURED WHEN CONNECTED TO L AUTOPLT. THE FO QUESTIONED TWR REGARDING RWY 17L VISIBILITY; WE COULD NOT SEE THE RWY. TWR CTLR RESPONDED WITH RWY VISIBILITY THAT REQUIRED AN ACFT CAT 3 AUTO LAND OP. AT 1700 FT AGL; I REENGAGED CTR AND R AUTOPLT. AT 1400 FT AGL; ACFT COMPLETED ITS OWN TEST AND INDICATED LAND 3. THE FO'S FLT INST INDICATIONS WERE NOW NORMAL LOC AND GS CAPTURED. FOR A MOMENT; EVERYTHING WAS COPASETIC. AS WE DSNDED THROUGH 700 FT AGL THE ACFT ASA DOWNGRADED EQUIVALENT TO CAT 1 STATUS; SO I COMPLETED A NORMAL MISSED APCH; GAR PROC. EVEN DIRECTLY OVERHEAD; I DID NOT VISUALLY ACQUIRE ANY PORTION OF RWY 17L. ON TOP OF THE FOG BANK BLANKETING THE RWY; IT WAS A BEAUTIFUL DAY IN ZZZZ. THAT'S ALL THE HALF ENGLISH SPEAKING PAX WOULD REMEMBER. ZZZZ OPS TOLD OUR FLT ATTENDANTS AND CUSTOMERS THAT THERE WAS NO REASON FOR US TO GO AROUND; THE VISIBILITY OVER THEIR DESK TOPS WAS PERFECT. OUR CURRENT ACFT AND RWY STATUS; COUPLED WITH ACFT ARRIVING ZZZZ FROM ALL DIRECTIONS; I ELECTED TO DIVERT TO ZZZZ1. IT WAS DIFFICULT WORKING/COMMUNICATING WITH THE AIR TFC CTLRS ON THIS PARTICULAR FLT/DAY; MY EXPERIENCE TOLD ME THAT AFTER MAKING IT AROUND THE PATTERN IN THE VALLEY COULD PUT US WELL BEHIND THE FUEL CURVE TO SAFELY DIVERT TO ZZZZ1. ADDITIONALLY; CREW FATIGUE WAS ALSO POSSIBLY A FACTOR. ONCE SAFELY ON THE GND IN ZZZZ1; WE LEARNED THAT ACFT HISTORY INCLUDED MANY PROBS WITH THE CTR AND RIGHT AUTOPLTS OVER A PERIOD OF TIME COVERING 54 LEGS OF FLYING. IN THE PAST; ALL AUTOPLT FAULTS ON THIS ACFT; AS PER THE MAINT LOG WERE SUCCESSFULLY RESET ON THE GND.

Data retrieved from NASA's ASRS site as of May 2009 and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.