Narrative:

First officer flying 80 NM north northwest of ZZZ. Upon passing FL240 for cruise altitude; airspeed at 310 KIAS; or so. Without warning; the autoplt and autothrottle disconnected and the plane made a very rapid snap roll to the right and airspeed bled off. It felt like an engine failure; deployed thrust reverser; or hard over rudder. I took manual control of the plane and was unable to maintain level flight with the yoke almost full back (FL240) and trimming nose up. The aircraft was very difficult to control in roll; pitch and yaw. All flight control inputs were either almost non-responsive or unpredictable (dutch roll; porpoising). (This thing did not fly like any aircraft I had ever flown before; like it had a mind of its own.) after a very brief discussion; the decision was made to declare an emergency and return to ZZZ (the closest airport). After another brief discussion; the decision was also made to have the first officer continue flying; as I was; at that point; most familiar with the plane's flight characteristics (or lack thereof). An appropriate checklist could not be found. All flight guidance panel annunciators and controls were completely inoperative; except the navigation radios. Since we were unable to maintain altitude; intermediate leveloffs were refused and a steady descent to ZZZ was requested. As we started descending; the aircraft started a very pronounced dutch roll -- flight attendants had great difficulty standing up in cabin. We requested; and were then vectored to an opposite direction landing as we did not feel comfortable with the plane's ability to negotiate any turns of more than a few degrees. We stabilized on a 10 mi final fully configured and made an overweight uneventful landing. The plane was difficult to control all the way to touchdown. At the time; I thought the odds were pretty good that we were going to die.callback conversation with reporter revealed the following information: several days after the event; the reporter passed through the station where the aircraft was left and was told by a mechanic who worked the aircraft that initially a popped circuit breaker was discovered that could not be reset. Assuming a circuit breaker failure; the circuit breaker was replaced; but still could not be reset. Maintenance began troubleshooting the wiring and found a chafed wire in the rudder area. The reporter did not remember which circuit breaker the mechanic said had popped. Concerning the flight event; the aircraft was much less controllable at higher altitudes than lower altitudes. Reporter felt if the aircraft had been at a higher cruise altitude at the event initiation they could not have controled it. All flight guidance annunciation was inoperative including the flight director command bars. They did have VOR frequency control. The initiation of the event was the rapid roll to 20 degrees with an airspeed loss and an attitude pitch down. The altitude alert window setting was locked at cruise altitude and remained there even after landing. At no time during the event did the crew have the slightest idea what was causing the instability. The rudder pedals were not moving autonomously with the oscillations. Confusing them even more was an intermittent mach trim failure annunciation. They discussed removing flight control systems; including rudder and yaw dampener; but decided no configuration change may be the best course for fear of worsening their status. At higher altitudes the porpoising was most pronounced while at lower altitudes the dutch roll increased greatly. In the landing configuration; the aircraft was still difficult to control. The first officer flew the aircraft throughout the event because the captain felt he had the best feel for what was occurring. Supplemental information from acn 666494: climbing through approximately 20000 ft; autoplt disconnected; all flight guidance functions became inoperative. Aircraft was unstable in roll and yaw; difficult to fly. Emergency was declared with ZZZ center and returned to departure airport. Aircraft was more controllable at lower altitudes/slower speeds. No annunciator lights except for intermittent 'mach trim.' circuit breaker for mach trim was pulled. No effect on control. Flight attendants were briefed; overweight landing accomplished at 134000 pounds. Configured early; straight in landing at ZZZ was uneventful.

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Original NASA ASRS Text

Title: AN MD80 EXPERIENCED UNCTLED ROLL; PITCH; AND YAW OSCILLATIONS AND A FLT GUIDANCE ANNUNCIATOR PANEL FAILURE. THE CREW DECLARED AN EMER; AND RETURNED TO LAND AT THE DEP ARPT. MAINT FOUND A CHAFED WIRE IN THE RUDDER AREA AND A POPPED CB WHICH COULD NOT BE RESET.

Narrative: FO FLYING 80 NM N NW OF ZZZ. UPON PASSING FL240 FOR CRUISE ALT; AIRSPD AT 310 KIAS; OR SO. WITHOUT WARNING; THE AUTOPLT AND AUTOTHROTTLE DISCONNECTED AND THE PLANE MADE A VERY RAPID SNAP ROLL TO THE R AND AIRSPD BLED OFF. IT FELT LIKE AN ENGINE FAILURE; DEPLOYED THRUST REVERSER; OR HARD OVER RUDDER. I TOOK MANUAL CTL OF THE PLANE AND WAS UNABLE TO MAINTAIN LEVEL FLT WITH THE YOKE ALMOST FULL BACK (FL240) AND TRIMMING NOSE UP. THE ACFT WAS VERY DIFFICULT TO CTL IN ROLL; PITCH AND YAW. ALL FLT CTL INPUTS WERE EITHER ALMOST NON-RESPONSIVE OR UNPREDICTABLE (DUTCH ROLL; PORPOISING). (THIS THING DID NOT FLY LIKE ANY ACFT I HAD EVER FLOWN BEFORE; LIKE IT HAD A MIND OF ITS OWN.) AFTER A VERY BRIEF DISCUSSION; THE DECISION WAS MADE TO DECLARE AN EMER AND RETURN TO ZZZ (THE CLOSEST ARPT). AFTER ANOTHER BRIEF DISCUSSION; THE DECISION WAS ALSO MADE TO HAVE THE FO CONTINUE FLYING; AS I WAS; AT THAT POINT; MOST FAMILIAR WITH THE PLANE'S FLT CHARACTERISTICS (OR LACK THEREOF). AN APPROPRIATE CHKLIST COULD NOT BE FOUND. ALL FLT GUIDANCE PANEL ANNUNCIATORS AND CTLS WERE COMPLETELY INOP; EXCEPT THE NAV RADIOS. SINCE WE WERE UNABLE TO MAINTAIN ALT; INTERMEDIATE LEVELOFFS WERE REFUSED AND A STEADY DSCNT TO ZZZ WAS REQUESTED. AS WE STARTED DSNDING; THE ACFT STARTED A VERY PRONOUNCED DUTCH ROLL -- FLT ATTENDANTS HAD GREAT DIFFICULTY STANDING UP IN CABIN. WE REQUESTED; AND WERE THEN VECTORED TO AN OPPOSITE DIRECTION LNDG AS WE DID NOT FEEL COMFORTABLE WITH THE PLANE'S ABILITY TO NEGOTIATE ANY TURNS OF MORE THAN A FEW DEGREES. WE STABILIZED ON A 10 MI FINAL FULLY CONFIGURED AND MADE AN OVERWEIGHT UNEVENTFUL LNDG. THE PLANE WAS DIFFICULT TO CTL ALL THE WAY TO TOUCHDOWN. AT THE TIME; I THOUGHT THE ODDS WERE PRETTY GOOD THAT WE WERE GOING TO DIE.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: SEVERAL DAYS AFTER THE EVENT; THE RPTR PASSED THROUGH THE STATION WHERE THE ACFT WAS LEFT AND WAS TOLD BY A MECHANIC WHO WORKED THE ACFT THAT INITIALLY A POPPED CB WAS DISCOVERED THAT COULD NOT BE RESET. ASSUMING A CB FAILURE; THE CB WAS REPLACED; BUT STILL COULD NOT BE RESET. MAINT BEGAN TROUBLESHOOTING THE WIRING AND FOUND A CHAFED WIRE IN THE RUDDER AREA. THE RPTR DID NOT REMEMBER WHICH CB THE MECHANIC SAID HAD POPPED. CONCERNING THE FLT EVENT; THE ACFT WAS MUCH LESS CONTROLLABLE AT HIGHER ALTS THAN LOWER ALTS. RPTR FELT IF THE ACFT HAD BEEN AT A HIGHER CRUISE ALT AT THE EVENT INITIATION THEY COULD NOT HAVE CTLED IT. ALL FLT GUIDANCE ANNUNCIATION WAS INOP INCLUDING THE FLT DIRECTOR COMMAND BARS. THEY DID HAVE VOR FREQUENCY CTL. THE INITIATION OF THE EVENT WAS THE RAPID ROLL TO 20 DEGS WITH AN AIRSPD LOSS AND AN ATTITUDE PITCH DOWN. THE ALT ALERT WINDOW SETTING WAS LOCKED AT CRUISE ALT AND REMAINED THERE EVEN AFTER LNDG. AT NO TIME DURING THE EVENT DID THE CREW HAVE THE SLIGHTEST IDEA WHAT WAS CAUSING THE INSTABILITY. THE RUDDER PEDALS WERE NOT MOVING AUTONOMOUSLY WITH THE OSCILLATIONS. CONFUSING THEM EVEN MORE WAS AN INTERMITTENT MACH TRIM FAILURE ANNUNCIATION. THEY DISCUSSED REMOVING FLT CTL SYSTEMS; INCLUDING RUDDER AND YAW DAMPENER; BUT DECIDED NO CONFIGURATION CHANGE MAY BE THE BEST COURSE FOR FEAR OF WORSENING THEIR STATUS. AT HIGHER ALTS THE PORPOISING WAS MOST PRONOUNCED WHILE AT LOWER ALTS THE DUTCH ROLL INCREASED GREATLY. IN THE LNDG CONFIGURATION; THE ACFT WAS STILL DIFFICULT TO CTL. THE FO FLEW THE ACFT THROUGHOUT THE EVENT BECAUSE THE CAPT FELT HE HAD THE BEST FEEL FOR WHAT WAS OCCURRING. SUPPLEMENTAL INFO FROM ACN 666494: CLBING THROUGH APPROX 20000 FT; AUTOPLT DISCONNECTED; ALL FLT GUIDANCE FUNCTIONS BECAME INOPERATIVE. ACFT WAS UNSTABLE IN ROLL AND YAW; DIFFICULT TO FLY. EMER WAS DECLARED WITH ZZZ CTR AND RETURNED TO DEP ARPT. ACFT WAS MORE CONTROLLABLE AT LOWER ALTS/SLOWER SPDS. NO ANNUNCIATOR LIGHTS EXCEPT FOR INTERMITTENT 'MACH TRIM.' CB FOR MACH TRIM WAS PULLED. NO EFFECT ON CONTROL. FLT ATTENDANTS WERE BRIEFED; OVERWEIGHT LNDG ACCOMPLISHED AT 134000 LBS. CONFIGURED EARLY; STRAIGHT IN LNDG AT ZZZ WAS UNEVENTFUL.

Data retrieved from NASA's ASRS site as of January 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.