AN MD80 OSCILLATED APPROX 5 DEGS AT 30 SECOND INTERVALS WITH THE AUTOPLT ENGAGED AND THE MACH TRIM SLIGHTLY ACTIVATED. THE CREW DECLARED AN EMER AND DIVERTED.

Narrative

ON DEP AT APPROX 14000 FT WITH THE AUTOPLT ENGAGED; I NOTICED THE CTL COLUMN CYCLING FORWARD AND AFT ONCE EVERY 20 SECONDS. AT FIRST I THOUGHT IT WAS BECAUSE I WAS CLBING OUT IN PERF. I DISCONNECTED PERF AND CLBED USING MACH HOLD AND EPR LIMIT. THIS HAD NO EFFECT AND THE CONTROL COLUMN CONTINUED TO CYCLE FORWARD AND AFT ONCE EVERY 20-30 SECONDS. UPON REACHING CRUISE ALT 33000 FT WITH THE AUTOPLT ENGAGED; THE CTL COLUMN CONTINUED TO CYCLE FORWARD AND AFT. I DISCONNECTED THE AUTOPLT AND HAND FLEW THE ACFT AND NOTICED THE CTL COLUMN CONTINUED TO CYCLE FORWARD AND AFT. AT THIS POINT; I HAD THE FO TAKE THE CTLS OF THE ACFT TO SEE IF HE COULD FEEL AND SEE WHAT I WAS EXPERIENCING. HE HAD THE SAME INDICATIONS AND THE SAME CTL COLUMN INPUTS AS I DID. AT THIS POINT; WE RE-ENGAGED THE AUTOPLT AND REFERRED TO THE QRH TO SEE IF THERE WAS ANYTHING RELATED TO THIS TYPE OF FLT CTL 'ABNORMALITY.' THERE WAS NOTHING SPECIFIC TO WHAT WE WERE EXPERIENCING ON OUR ACFT. I THEN CONTACTED A MAINT TECH VIA ACARS PHONE PATCH TO SEE IF THERE WAS ANY HISTORY OR PATTERNS OF THIS PARTICULAR TYPE OF FLT CTL ABNORMALITY ON THIS ACFT. I GAVE THE MAINT TECH THE DETAILS OF WHAT WE WERE EXPERIENCING AND THEY INFORMED ME THAT I SHOULD CONSIDER LNDG AS SOON AS PRACTICAL. I WAS IN TOTAL AGREEMENT BECAUSE AT THIS POINT I WAS ALREADY CONSIDERING LNDG. I TERMINATED THE PHONE PATCH WITH MAINT AND CONTACTED DISPATCH TO LET THEM KNOW THAT I WOULD BE DIVERTING TO EITHER ZZZ1 OR ZZZ2. HE RECOMMENDED ZZZ1 BECAUSE IT WAS ABOUT THE SAME DISTANCE TO ZZZ2; AND ZZZ1 HAD OPPORTUNITIES FOR CONNECTING PAX. I TOLD THE DISPATCHER THAT WE WERE IN THE TURN BACK TO ZZZ1 AND HE ASKED ME IF I HAD DECLARED AN EMER. I TOLD HIM AT THIS POINT WE HAD NOT DECLARED AN EMER BUT I WOULD AS SOON AS CONDITIONS PERMITTED AND I WOULD RELAY EVERYTHING THROUGH ATC. ONCE THE ACFT WAS HEADED W BOUND; I DECLARED AN EMER WITH ATC FOR FLT CTL MALFUNCTION. I FELT THAT THE SIT WAS NOT GETTING ANY BETTER AND MY EXPERIENCE WITH T-TAILED ACFT TOLD ME THAT AS YOU GET LIGHTER; THESE TYPES OF FLT CTL PROBS GET WORSE AS THE ACFT GETS LIGHTER. WE MADE A NORMAL ENRTE DSCNT AND VISUAL APCH TO LNDG. AS WE WERE IN THE DSCNT; I RECEIVED AN ACARS MESSAGE FROM MAINT TELLING ME TO TRY TURNING THE MACH TRIM SWITCH TO OVERRIDE. WE DID THIS IN THE DSCNT BUT HAD NO EFFECT ON THE PROB. ACFT LNDG IN ZZZ1 OVERWEIGHT WITH NO PROBS. EMER WAS TERMINATED UPON LNDG ROLLOUT. CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: CAPT RPTS THAT AT LEAST 2 ISSUES WERE INVOLVED IN THIS INCIDENT. ONE WAS FAULTY ANGLE OF ATTACK (AOA) SYSTEM AND THE SECOND #2 VERTICAL GYRO. GND MAINT DISCOVERED THE AOA DISCREPANCY AND A FLT TEST CREW DISCOVERED THE GYRO. THE ANGLE OF ATTACK FAULT WAS ATTEMPTING TO ACTIVATE THE STALL WARNING SYSTEM WHICH EXPLAINS WHY THE MACH TRIM WAS PARTIALLY ACTIVATED. THE #2 GYRO WAS CAUSING THE AUTOPLT TO 'BURP' AT 30 SECOND INTERVALS AS THE GYRO FLUCTUATED. THIS CREW WAS NOT INTERESTED IN TROUBLESHOOTING THE PROB INFLT BECAUSE THERE WERE BEHAVIORS THEY DID NOT UNDERSTAND AND SINCE THE ACFT WAS CONTROLLABLE AT THE TIME THEY SIMPLY WANTED TO GET ON THE GND AND TROUBLESHOOT LATER. SUPPLEMENTAL INFO FROM ACN 665189: THE PFD WOULD ALSO JUMP ABOUT 5 DEGS NOSE UP THEN NOSE DOWN. I ALSO NOTICED THE MACH TRIM INDICATOR WAS EXTENDED PAST THE TIP ABOUT A TENTH OF AN INCH AND WE WERE ONLY FLYING MACH .75 WHICH SEEMED A LITTLE STRANGE. ADDITIONALLY; WE DISENGAGED THE AUTOPLT SEVERAL TIMES AND THE PROB WENT AWAY FOR THE MOST PART; HOWEVER; THERE WAS A RUMBLING FELT ON THE YOKE WHICH ALSO CONCERNED US. AT THAT POINT; WE BECAME REALLY CONCERNED THAT WE COULD HAVE A STABILIZER PROB. CALLBACK CONVERSATION WITH RPTR ACN 665189 REVEALED THE FOLLOWING INFO: FO RPTED THAT AFTER 3 DAYS OF TROUBLESHOOTING; MAINT DISCOVERED A RATE GYRO FAILURE IN THE #2 (FO'S) FLT CTL COMPUTER. THE RPTR STATED THAT HE HAS 9000 HRS IN TYPE AND HAS NEVER EXPERIENCED THIS BEFORE. THEY WERE TRULY CONCERNED ABOUT THE ACFT'S CONDITION. RPTR FORWARDED THE MAINT DEPT'S ANALYSIS OF THE TROUBLESHOOTING AND FLT TESTING ACCOMPLISHED IN ORDER TO DEFINITIVELY SOLVE THIS PROB. THE RPT'S CONCLUSION STATED; 'AND... THIS TEST CREW SAID THIS ISN'T THE FIRST FCF THEY HAVE FLOWN FOR THIS VERY SAME CONDITION ON OTHER MD80'S... AND THE FIX HAS ALWAYS BEEN THE #1 OR #2 VG. GOOD INFO FOR MD80 CREWS TO KNOW TO SWITCHING TO THE AUX VG IF THEY HAVE EVER HAVE THIS CONDITION.