Narrative:

We were delayed due to a late arriving aircraft and because maintenance had to replace elac-1. On departure; I noted what I thought of as 'slipperiness;' it seemed like the airplane was slipping a little; as if driving on an icy road. Along with some light chop; we had configuration; speed; thrust and altitude changes which masked the situation enough that I thought it was just my being paranoid. During the climb; I didn't notice anything unusual once above about 10-15;000 ft; where the air smoothed out. This made me sure that the unusual feel was from the turbulence. On descent into ZZZ; I disengaged the autopilot in smooth air and immediately noticed a jerky; yaw. I think it had been there before; but it was more noticeable when hand-flying due to knowing which inputs were mine vs the computer's. There was no rhythm or smoothness to it. It seemed random; would sometimes jerk left; then left again before jerking right. I then told my first officer that 'that's not me' and we started discussing the situation. The airplane's nose was jerking back and forth in yaw in small; random movements. It was more significant in turns. During those turns; the slip indicator showed serious deviations in both directions. The excursions during the roll-in and roll-out were relatively large; and they were also the same way when in a stabilized bank. We paid very close attention to the flight control page once we discovered the anomaly; and to us; it looked like the rudder was being commanded to do what it was doing. I was later asked by maintenance if I thought it could have been a loose actuator or bearing; but having had that problem before; I don't believe it was. There was no vibration that I could feel at any time during the flight; and the movements of the rudder were larger and more deliberate. These weren't yawing movements related to anything like a dutch roll. They weren't rhythmic or gentle; but random and twitchy. There was no related pitch or roll. Nor were they associated with engine thrust; speed; altitude or configuration changes or other flight control movements. We had no ECAM error or failure messages; but the rudder itself was moving enough to see it on the flight control synopsis page. It was moving from one side of the small box at the bottom of the rudder scale to the other. It showed the twitching exactly as we felt it. After a brief conversation with my first officer; I decided to declare an emergency; climb back up to 5;000 ft; and contact company and plan to divert to ZZZ1. Maintenance said they were uncomfortable with doing any flight control computer resets while in flight (I wholeheartedly concurred with that) so there wasn't much we could do about it. Maintenance patched dispatch in to the conversation; and I told them that we were going to divert to ZZZ1 after fully configuring for landing and doing a controllability check. Everyone concurred. I called the purser up to the cockpit where I briefed her on our problem; and that because one of our flight controls was doing things we weren't asking it to do; we would do a full cabin prep for evacuation. We discussed how we were going to configure and do a controllability check; and then started to proceed with it. Once fully configured; I turned the airplane about 30 degrees left and right by using both the autopilot and hand-flying. The rudder was still kicking a bit left and right; but in turns; it was really noticeable. We decided to try to take as many computers out of the system as possible; so I would hand fly the final approach from glideslope intercept to touchdown. Although the rudder was still jerking as much as it was previously; the airplane was completely controllable. And with the gear down (as well as with the flaps and slats out) the airplane became significantly more stable. We could still feel slight twitches but their severity was almost gone; and we could see the same movements on the flight control page as before; but we were guessing that the increased drag of the gear was helping stabilize us. When we were about 100 ft - 200 ft AGL; the first officer made the brace call on the PA. At about the same time; the rudder surprised me by kicking significantly. Once in the flare and taking out the crab; the rudder settled down some; making the airplane completely and precisely controllable again. Once the nose gear was on the runway; the first officer made the 'remain seated' PA call; just as briefed; and he once again said it as we cleared the runway. After the passengers were off; I gathered the crew together at mid-cabin to perform a mini-debrief. First; I asked everyone if they were ok; and then I discussed the physiological issues we were facing. I told them that I had had an incident once before where we ended up with a full cabin prep; and that in about 15 minutes to an hour or so; we would all 'hit a wall' when the extreme adrenaline rush wore off. I told them that I wanted them to be completely honest; and I asked them each individually whether they wanted to go on to ZZZ or stop here in ZZZ1 (I was last to answer; by the way.) each crewmember answered that they wanted to stop here; which agreed with my assessment exactly. I informed all the supervisors that were still at the airplane of my decision to pull the crew from scheduled flying until we got proper rest. To be clear; if anyone in the system has a problem with this; this was my decision to pull the crew and insist on rest. I took the crew's input and made a command decision based on my experience and on a spot judgment. If there are any repercussions to this; they should all fall on me; and not on any other member(south) of the crew. Lessons from this incident: after being on the airplane for 3 years now; I should probably respect my feelings about 'this doesn't' feel right a little more; even if it's just a little 'not right' and hard to put your finger on exactly what's wrong. Also; the yaw excursions were actually slight in the big scheme of things; but since we don't ever get them like this; they were definitely noticeable on the descent; especially at the lower altitudes. I doubt that a flight attendant; unless she were at the extreme tail of the airplane; would have fallen down as a result of the jerking rudder except during a turn executed below 8;000 ft; as that's where it seemed worst. It was definitely noticeable; and I would have had the seatbelt sign on for that much movement; turns or straight and level; under any circumstances; though.callback conversation with reporter revealed the following information: the reporter stated that he called his air carrier's maintenance several days later and discovered that his flight's rudder problem was caused by an elevator fault. Following the reporter's event; an elac was changed to address the elevator fault and the aircraft released. That new elac was the third in two days. The reporter indicated that on the next day on a revenue flight that crew experienced a pitch up; adding the crew declared an emergency and diverted. The reporter was told following that event more in-depth elevator investigation and repair was completed.

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Original NASA ASRS Text

Title: AN A320 CREW EXPERIENCED SPURIOUS RUDDER DEFLECTIONS CAUSED BY AN ELEVATOR FAULT. AN EMER WAS DECLARED WITH AN ARPT DIVERSION.

Narrative: WE WERE DELAYED DUE TO A LATE ARRIVING ACFT AND BECAUSE MAINTENANCE HAD TO REPLACE ELAC-1. ON DEPARTURE; I NOTED WHAT I THOUGHT OF AS 'SLIPPERINESS;' IT SEEMED LIKE THE AIRPLANE WAS SLIPPING A LITTLE; AS IF DRIVING ON AN ICY ROAD. ALONG WITH SOME LIGHT CHOP; WE HAD CONFIGURATION; SPEED; THRUST AND ALTITUDE CHANGES WHICH MASKED THE SITUATION ENOUGH THAT I THOUGHT IT WAS JUST MY BEING PARANOID. DURING THE CLIMB; I DIDN'T NOTICE ANYTHING UNUSUAL ONCE ABOVE ABOUT 10-15;000 FT; WHERE THE AIR SMOOTHED OUT. THIS MADE ME SURE THAT THE UNUSUAL FEEL WAS FROM THE TURBULENCE. ON DESCENT INTO ZZZ; I DISENGAGED THE AUTOPILOT IN SMOOTH AIR AND IMMEDIATELY NOTICED A JERKY; YAW. I THINK IT HAD BEEN THERE BEFORE; BUT IT WAS MORE NOTICEABLE WHEN HAND-FLYING DUE TO KNOWING WHICH INPUTS WERE MINE VS THE COMPUTER'S. THERE WAS NO RHYTHM OR SMOOTHNESS TO IT. IT SEEMED RANDOM; WOULD SOMETIMES JERK LEFT; THEN LEFT AGAIN BEFORE JERKING RIGHT. I THEN TOLD MY FO THAT 'THAT'S NOT ME' AND WE STARTED DISCUSSING THE SITUATION. THE AIRPLANE'S NOSE WAS JERKING BACK AND FORTH IN YAW IN SMALL; RANDOM MOVEMENTS. IT WAS MORE SIGNIFICANT IN TURNS. DURING THOSE TURNS; THE SLIP INDICATOR SHOWED SERIOUS DEVIATIONS IN BOTH DIRECTIONS. THE EXCURSIONS DURING THE ROLL-IN AND ROLL-OUT WERE RELATIVELY LARGE; AND THEY WERE ALSO THE SAME WAY WHEN IN A STABILIZED BANK. WE PAID VERY CLOSE ATTENTION TO THE FLIGHT CONTROL PAGE ONCE WE DISCOVERED THE ANOMALY; AND TO US; IT LOOKED LIKE THE RUDDER WAS BEING COMMANDED TO DO WHAT IT WAS DOING. I WAS LATER ASKED BY MAINTENANCE IF I THOUGHT IT COULD HAVE BEEN A LOOSE ACTUATOR OR BEARING; BUT HAVING HAD THAT PROBLEM BEFORE; I DON'T BELIEVE IT WAS. THERE WAS NO VIBRATION THAT I COULD FEEL AT ANY TIME DURING THE FLIGHT; AND THE MOVEMENTS OF THE RUDDER WERE LARGER AND MORE DELIBERATE. THESE WEREN'T YAWING MOVEMENTS RELATED TO ANYTHING LIKE A DUTCH ROLL. THEY WEREN'T RHYTHMIC OR GENTLE; BUT RANDOM AND TWITCHY. THERE WAS NO RELATED PITCH OR ROLL. NOR WERE THEY ASSOCIATED WITH ENGINE THRUST; SPEED; ALTITUDE OR CONFIGURATION CHANGES OR OTHER FLIGHT CONTROL MOVEMENTS. WE HAD NO ECAM ERROR OR FAILURE MESSAGES; BUT THE RUDDER ITSELF WAS MOVING ENOUGH TO SEE IT ON THE FLIGHT CONTROL SYNOPSIS PAGE. IT WAS MOVING FROM ONE SIDE OF THE SMALL BOX AT THE BOTTOM OF THE RUDDER SCALE TO THE OTHER. IT SHOWED THE TWITCHING EXACTLY AS WE FELT IT. AFTER A BRIEF CONVERSATION WITH MY FO; I DECIDED TO DECLARE AN EMERGENCY; CLIMB BACK UP TO 5;000 FT; AND CONTACT COMPANY AND PLAN TO DIVERT TO ZZZ1. MAINT SAID THEY WERE UNCOMFORTABLE WITH DOING ANY FLIGHT CONTROL COMPUTER RESETS WHILE IN FLIGHT (I WHOLEHEARTEDLY CONCURRED WITH THAT) SO THERE WASN'T MUCH WE COULD DO ABOUT IT. MAINT PATCHED DISPATCH IN TO THE CONVERSATION; AND I TOLD THEM THAT WE WERE GOING TO DIVERT TO ZZZ1 AFTER FULLY CONFIGURING FOR LANDING AND DOING A CONTROLLABILITY CHECK. EVERYONE CONCURRED. I CALLED THE PURSER UP TO THE COCKPIT WHERE I BRIEFED HER ON OUR PROBLEM; AND THAT BECAUSE ONE OF OUR FLIGHT CONTROLS WAS DOING THINGS WE WEREN'T ASKING IT TO DO; WE WOULD DO A FULL CABIN PREP FOR EVACUATION. WE DISCUSSED HOW WE WERE GOING TO CONFIGURE AND DO A CONTROLLABILITY CHECK; AND THEN STARTED TO PROCEED WITH IT. ONCE FULLY CONFIGURED; I TURNED THE AIRPLANE ABOUT 30 DEGS LEFT AND RIGHT BY USING BOTH THE AUTOPILOT AND HAND-FLYING. THE RUDDER WAS STILL KICKING A BIT LEFT AND RIGHT; BUT IN TURNS; IT WAS REALLY NOTICEABLE. WE DECIDED TO TRY TO TAKE AS MANY COMPUTERS OUT OF THE SYSTEM AS POSSIBLE; SO I WOULD HAND FLY THE FINAL APPROACH FROM GLIDESLOPE INTERCEPT TO TOUCHDOWN. ALTHOUGH THE RUDDER WAS STILL JERKING AS MUCH AS IT WAS PREVIOUSLY; THE AIRPLANE WAS COMPLETELY CONTROLLABLE. AND WITH THE GEAR DOWN (AS WELL AS WITH THE FLAPS AND SLATS OUT) THE AIRPLANE BECAME SIGNIFICANTLY MORE STABLE. WE COULD STILL FEEL SLIGHT TWITCHES BUT THEIR SEVERITY WAS ALMOST GONE; AND WE COULD SEE THE SAME MOVEMENTS ON THE FLT CONTROL PAGE AS BEFORE; BUT WE WERE GUESSING THAT THE INCREASED DRAG OF THE GEAR WAS HELPING STABILIZE US. WHEN WE WERE ABOUT 100 FT - 200 FT AGL; THE FO MADE THE BRACE CALL ON THE PA. AT ABOUT THE SAME TIME; THE RUDDER SURPRISED ME BY KICKING SIGNIFICANTLY. ONCE IN THE FLARE AND TAKING OUT THE CRAB; THE RUDDER SETTLED DOWN SOME; MAKING THE AIRPLANE COMPLETELY AND PRECISELY CONTROLLABLE AGAIN. ONCE THE NOSE GEAR WAS ON THE RUNWAY; THE FO MADE THE 'REMAIN SEATED' PA CALL; JUST AS BRIEFED; AND HE ONCE AGAIN SAID IT AS WE CLEARED THE RUNWAY. AFTER THE PASSENGERS WERE OFF; I GATHERED THE CREW TOGETHER AT MID-CABIN TO PERFORM A MINI-DEBRIEF. FIRST; I ASKED EVERYONE IF THEY WERE OK; AND THEN I DISCUSSED THE PHYSIOLOGICAL ISSUES WE WERE FACING. I TOLD THEM THAT I HAD HAD AN INCIDENT ONCE BEFORE WHERE WE ENDED UP WITH A FULL CABIN PREP; AND THAT IN ABOUT 15 MINUTES TO AN HOUR OR SO; WE WOULD ALL 'HIT A WALL' WHEN THE EXTREME ADRENALINE RUSH WORE OFF. I TOLD THEM THAT I WANTED THEM TO BE COMPLETELY HONEST; AND I ASKED THEM EACH INDIVIDUALLY WHETHER THEY WANTED TO GO ON TO ZZZ OR STOP HERE IN ZZZ1 (I WAS LAST TO ANSWER; BY THE WAY.) EACH CREWMEMBER ANSWERED THAT THEY WANTED TO STOP HERE; WHICH AGREED WITH MY ASSESSMENT EXACTLY. I INFORMED ALL THE SUPERVISORS THAT WERE STILL AT THE AIRPLANE OF MY DECISION TO PULL THE CREW FROM SCHEDULED FLYING UNTIL WE GOT PROPER REST. TO BE CLEAR; IF ANYONE IN THE SYSTEM HAS A PROBLEM WITH THIS; THIS WAS MY DECISION TO PULL THE CREW AND INSIST ON REST. I TOOK THE CREW'S INPUT AND MADE A COMMAND DECISION BASED ON MY EXPERIENCE AND ON A SPOT JUDGMENT. IF THERE ARE ANY REPERCUSSIONS TO THIS; THEY SHOULD ALL FALL ON ME; AND NOT ON ANY OTHER MEMBER(S) OF THE CREW. LESSONS FROM THIS INCIDENT: AFTER BEING ON THE AIRPLANE FOR 3 YEARS NOW; I SHOULD PROBABLY RESPECT MY FEELINGS ABOUT 'THIS DOESN'T' FEEL RIGHT A LITTLE MORE; EVEN IF IT'S JUST A LITTLE 'NOT RIGHT' AND HARD TO PUT YOUR FINGER ON EXACTLY WHAT'S WRONG. ALSO; THE YAW EXCURSIONS WERE ACTUALLY SLIGHT IN THE BIG SCHEME OF THINGS; BUT SINCE WE DON'T EVER GET THEM LIKE THIS; THEY WERE DEFINITELY NOTICEABLE ON THE DESCENT; ESPECIALLY AT THE LOWER ALTITUDES. I DOUBT THAT A FLIGHT ATTENDANT; UNLESS SHE WERE AT THE EXTREME TAIL OF THE AIRPLANE; WOULD HAVE FALLEN DOWN AS A RESULT OF THE JERKING RUDDER EXCEPT DURING A TURN EXECUTED BELOW 8;000 FT; AS THAT'S WHERE IT SEEMED WORST. IT WAS DEFINITELY NOTICEABLE; AND I WOULD HAVE HAD THE SEATBELT SIGN ON FOR THAT MUCH MOVEMENT; TURNS OR STRAIGHT AND LEVEL; UNDER ANY CIRCUMSTANCES; THOUGH.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE RPTR STATED THAT HE CALLED HIS ACR'S MAINT SEVERAL DAYS LATER AND DISCOVERED THAT HIS FLT'S RUDDER PROB WAS CAUSED BY AN ELEVATOR FAULT. FOLLOWING THE RPTR'S EVENT; AN ELAC WAS CHANGED TO ADDRESS THE ELEVATOR FAULT AND THE ACFT RELEASED. THAT NEW ELAC WAS THE THIRD IN TWO DAYS. THE RPTR INDICATED THAT ON THE NEXT DAY ON A REVENUE FLT THAT CREW EXPERIENCED A PITCH UP; ADDING THE CREW DECLARED AN EMER AND DIVERTED. THE RPTR WAS TOLD FOLLOWING THAT EVENT MORE IN-DEPTH ELEVATOR INVESTIGATION AND REPAIR WAS COMPLETED.

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.