Narrative:

Climbing and accelerating we started to notice an airframe vibration. It was a constant frequency vibration that was best described as driving a car over a washboard. We leveled off at FL280; 300 KIAS/.78 mach; and set up for a vibration check; working each flight control axis individually. Rudder input made the vibration stop. Engine parameters were normal; and the vibration was not associated with engine RPM and wasn't anywhere near the frequency that you get with an engine vibration problem. Airspeed was a factor in vibration amplitude. The faster we went; the larger the vibration; and conversely; the slower we went; the less the vibration. We slowed to 250 KIAS and maintained that until in the pattern back at ZZZ. During that time; both pilots could feel the vibration in the rudder pedals; but not in the airframe. In the pedals; it felt to me like it would shake a little and then build to 1 larger amplitude pop; then back to the small shakes. Now; don't get me wrong here; the pedal shaking was very small; but it was noticeable. We both experimented by putting our feet on the floor; which was very smooth; and then on the pedals; which brought about that small vibration. While we were at altitude and troubleshooting the problem; we contacted maintenance and had them patch us through to dispatch. During that time; both the first officer and I confirmed that if we held still and stared at the pfd and navigation display; it appeared that they were vibrating back and forth laterally; that is; in yaw. Since they are bolted into the airframe; we concluded that it was we pilots who were being bounced left and right slightly; and that for us this was another confirmation that it was a rudder flutter problem. With dispatch and maintenance we discussed our options (continue; return to ZZZ; or land at the nearest suitable). I felt it was in the best interest of the company that a return to ZZZ was best; and maintenance concurred. Dispatch wanted to know if it was something we needed to land as soon as possible for; and it was my and my first officer's opinion that as long as we stayed at 250 KIAS or less; it was just fine to fly it back to ZZZ. That was the plan and that's what we did. I informed the flight attendants; and did a cabin advisory briefing with the purser. I informed the passenger of our problem and told them of our return to ZZZ. The approach; landing and taxi-in was uneventful.

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Original NASA ASRS Text

Title: AN A320 PILOT REPORTS AN AIRFRAME VIBRATION AT FL280/M0.78/300 KTS WHILE CLBING. AIRSPEED INCREASED VIBRATION AND IT APPEARED ASSOCIATED WITH THE RUDDER.

Narrative: CLBING AND ACCELERATING WE STARTED TO NOTICE AN AIRFRAME VIBRATION. IT WAS A CONSTANT FREQ VIBRATION THAT WAS BEST DESCRIBED AS DRIVING A CAR OVER A WASHBOARD. WE LEVELED OFF AT FL280; 300 KIAS/.78 MACH; AND SET UP FOR A VIBRATION CHK; WORKING EACH FLT CTL AXIS INDIVIDUALLY. RUDDER INPUT MADE THE VIBRATION STOP. ENG PARAMETERS WERE NORMAL; AND THE VIBRATION WAS NOT ASSOCIATED WITH ENG RPM AND WASN'T ANYWHERE NEAR THE FREQ THAT YOU GET WITH AN ENG VIBRATION PROB. AIRSPD WAS A FACTOR IN VIBRATION AMPLITUDE. THE FASTER WE WENT; THE LARGER THE VIBRATION; AND CONVERSELY; THE SLOWER WE WENT; THE LESS THE VIBRATION. WE SLOWED TO 250 KIAS AND MAINTAINED THAT UNTIL IN THE PATTERN BACK AT ZZZ. DURING THAT TIME; BOTH PLTS COULD FEEL THE VIBRATION IN THE RUDDER PEDALS; BUT NOT IN THE AIRFRAME. IN THE PEDALS; IT FELT TO ME LIKE IT WOULD SHAKE A LITTLE AND THEN BUILD TO 1 LARGER AMPLITUDE POP; THEN BACK TO THE SMALL SHAKES. NOW; DON'T GET ME WRONG HERE; THE PEDAL SHAKING WAS VERY SMALL; BUT IT WAS NOTICEABLE. WE BOTH EXPERIMENTED BY PUTTING OUR FEET ON THE FLOOR; WHICH WAS VERY SMOOTH; AND THEN ON THE PEDALS; WHICH BROUGHT ABOUT THAT SMALL VIBRATION. WHILE WE WERE AT ALT AND TROUBLESHOOTING THE PROB; WE CONTACTED MAINT AND HAD THEM PATCH US THROUGH TO DISPATCH. DURING THAT TIME; BOTH THE FO AND I CONFIRMED THAT IF WE HELD STILL AND STARED AT THE PFD AND NAV DISPLAY; IT APPEARED THAT THEY WERE VIBRATING BACK AND FORTH LATERALLY; THAT IS; IN YAW. SINCE THEY ARE BOLTED INTO THE AIRFRAME; WE CONCLUDED THAT IT WAS WE PLTS WHO WERE BEING BOUNCED L AND R SLIGHTLY; AND THAT FOR US THIS WAS ANOTHER CONFIRMATION THAT IT WAS A RUDDER FLUTTER PROB. WITH DISPATCH AND MAINT WE DISCUSSED OUR OPTIONS (CONTINUE; RETURN TO ZZZ; OR LAND AT THE NEAREST SUITABLE). I FELT IT WAS IN THE BEST INTEREST OF THE COMPANY THAT A RETURN TO ZZZ WAS BEST; AND MAINT CONCURRED. DISPATCH WANTED TO KNOW IF IT WAS SOMETHING WE NEEDED TO LAND ASAP FOR; AND IT WAS MY AND MY FO'S OPINION THAT AS LONG AS WE STAYED AT 250 KIAS OR LESS; IT WAS JUST FINE TO FLY IT BACK TO ZZZ. THAT WAS THE PLAN AND THAT'S WHAT WE DID. I INFORMED THE FLT ATTENDANTS; AND DID A CABIN ADVISORY BRIEFING WITH THE PURSER. I INFORMED THE PAX OF OUR PROB AND TOLD THEM OF OUR RETURN TO ZZZ. THE APCH; LNDG AND TAXI-IN 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.