Narrative:

We had been in a steady-state climb for about 10 min at 320 KIAS as we passed through FL260. At this time we started feeling an airframe vibration. In a matter of a few seconds the vibration went from slight to severe. As an example; the vibration in the cockpit was strong enough to 'spill your coffee.' we immediately started slowing the airplane and also received a call from the flight attendants. The flight attendant said the vibration was extremely bad and they were very concerned. The vibration was an up and down motion and could also be felt in the rudder pedals as the whole airplane was shaking. As we slowed through 310 KIAS the vibration lessened and at 290 KIAS we could no longer feel the vibration in the cockpit. The flight attendants could still feel a slight vibration at that speed. At 250 KIAS the vibration was no longer felt by the flight attendants. The first officer was the PF and as we began slowing I had him work the radios as I began to assess our situation. I told him to declare an emergency; plan on leveling off; and to tell ATC that we would be diverting; probably to ZZZ. At this time I also recalled that the aircraft had a high-speed vibration report in the maintenance history. I sent a 'call me' to dispatch and received a prompt response. After a short explanation of what was going on I told dispatch that I was planning on going to ZZZ if the WX was good unless he had another suggestion. Dispatch gave me the WX information and said ZZZ was fine. I then had the first officer tell ATC that we wanted to go to ZZZ and wanted to start a decent. The first officer flew a 240 KIAS descent and I told him not to use the speed brake if we were high. I didn't want anything messing with the airflow over the tail. Since the aircraft was under control and not vibrating; I took the time to speak with the flight attendants to explain our plan and issued a cabin advisory. I then told the passenger what was going on and that we would be on the ground in 20-25 min. I also told them that they would see emergency equipment upon landing and that it was just a precaution and we expected a normal landing. The first officer suggested looking at the checklist for a configuration check. I did that and we decided that the checklist itself didn't really apply but we did plan on configuring early to make sure the vibration did not return. On downwind we extended the flaps and gear and all felt normal. The first officer proceeded to fly us to a normal landing and we taxied to the gate. Some thoughts? ATC; dispatch; first officer; flight attendants all were excellent. Support after the incident by flight operations; dispatch; maintenance and union safety was also excellent. The only negative comment I have is that maintenance control asked dispatch to forward a request to fly to ZZZ1 if we could and if the plane was flying normally since we didn't have much maintenance support in ZZZ. From reading the message I would say dispatch didn't really agree with the message but forwarded it anyway. At the position we were in I think the message was inappropriate. I am guessing that maintenance control (and maybe dispatch) didn't have a real feel as to how serious the situation was at the time.callback conversation with reporter revealed the following information: the reporter stated that as far as he knows the rudder and elevator hinge bearings were changed; the aircraft test flown by air carrier test pilots and put back into service. He knows of no trigger that started what felt to him and the first officer like up and down flutters. They were climbing when a slight flutter started. In a period of 4-5 seconds it developed into a severe flutter. If the flight attendants in the back were not holding on to something they would have been on the floor. The crew believes the motion was stronger in the aircraft's aft than up front. This aircraft had a maintenance write up from 5 days prior that resulted in a flight crew flutter checklist completion. As far as this crew knows the aircraft is back in service.

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Original NASA ASRS Text

Title: AN A320 DEVELOPED SEVERE AIRFRAME VIBRATIONS AT 320 KTS CLBING THROUGH FL260. THE VIBRATIONS LESSENED AT 290 KTS. AN EMER WAS DECLARED FOLLOWED BY A LNDG AT A NEARBY ARPT.

Narrative: WE HAD BEEN IN A STEADY-STATE CLIMB FOR ABOUT 10 MIN AT 320 KIAS AS WE PASSED THROUGH FL260. AT THIS TIME WE STARTED FEELING AN AIRFRAME VIBRATION. IN A MATTER OF A FEW SECONDS THE VIBRATION WENT FROM SLIGHT TO SEVERE. AS AN EXAMPLE; THE VIBRATION IN THE COCKPIT WAS STRONG ENOUGH TO 'SPILL YOUR COFFEE.' WE IMMEDIATELY STARTED SLOWING THE AIRPLANE AND ALSO RECEIVED A CALL FROM THE FLIGHT ATTENDANTS. THE FLT ATTENDANT SAID THE VIBRATION WAS EXTREMELY BAD AND THEY WERE VERY CONCERNED. THE VIBRATION WAS AN UP AND DOWN MOTION AND COULD ALSO BE FELT IN THE RUDDER PEDALS AS THE WHOLE AIRPLANE WAS SHAKING. AS WE SLOWED THROUGH 310 KIAS THE VIBRATION LESSENED AND AT 290 KIAS WE COULD NO LONGER FEEL THE VIBRATION IN THE COCKPIT. THE FLT ATTENDANTS COULD STILL FEEL A SLIGHT VIBRATION AT THAT SPEED. AT 250 KIAS THE VIBRATION WAS NO LONGER FELT BY THE FLT ATTENDANTS. THE FO WAS THE PF AND AS WE BEGAN SLOWING I HAD HIM WORK THE RADIOS AS I BEGAN TO ASSESS OUR SITUATION. I TOLD HIM TO DECLARE AN EMERGENCY; PLAN ON LEVELING OFF; AND TO TELL ATC THAT WE WOULD BE DIVERTING; PROBABLY TO ZZZ. AT THIS TIME I ALSO RECALLED THAT THE ACFT HAD A HIGH-SPEED VIBRATION REPORT IN THE MAINT HISTORY. I SENT A 'CALL ME' TO DISPATCH AND RECEIVED A PROMPT RESPONSE. AFTER A SHORT EXPLANATION OF WHAT WAS GOING ON I TOLD DISPATCH THAT I WAS PLANNING ON GOING TO ZZZ IF THE WX WAS GOOD UNLESS HE HAD ANOTHER SUGGESTION. DISPATCH GAVE ME THE WX INFO AND SAID ZZZ WAS FINE. I THEN HAD THE FO TELL ATC THAT WE WANTED TO GO TO ZZZ AND WANTED TO START A DECENT. THE FO FLEW A 240 KIAS DESCENT AND I TOLD HIM NOT TO USE THE SPEED BRAKE IF WE WERE HIGH. I DIDN'T WANT ANYTHING MESSING WITH THE AIRFLOW OVER THE TAIL. SINCE THE ACFT WAS UNDER CONTROL AND NOT VIBRATING; I TOOK THE TIME TO SPEAK WITH THE FLT ATTENDANTS TO EXPLAIN OUR PLAN AND ISSUED A CABIN ADVISORY. I THEN TOLD THE PAX WHAT WAS GOING ON AND THAT WE WOULD BE ON THE GROUND IN 20-25 MIN. I ALSO TOLD THEM THAT THEY WOULD SEE EMERGENCY EQUIPMENT UPON LANDING AND THAT IT WAS JUST A PRECAUTION AND WE EXPECTED A NORMAL LANDING. THE FO SUGGESTED LOOKING AT THE CHECKLIST FOR A CONFIGURATION CHECK. I DID THAT AND WE DECIDED THAT THE CHECKLIST ITSELF DIDN'T REALLY APPLY BUT WE DID PLAN ON CONFIGURING EARLY TO MAKE SURE THE VIBRATION DID NOT RETURN. ON DOWNWIND WE EXTENDED THE FLAPS AND GEAR AND ALL FELT NORMAL. THE FO PROCEEDED TO FLY US TO A NORMAL LANDING AND WE TAXIED TO THE GATE. SOME THOUGHTS? ATC; DISPATCH; FO; FLT ATTENDANTS ALL WERE EXCELLENT. SUPPORT AFTER THE INCIDENT BY FLT OPS; DISPATCH; MAINT AND UNION SAFETY WAS ALSO EXCELLENT. THE ONLY NEGATIVE COMMENT I HAVE IS THAT MAINT CTL ASKED DISPATCH TO FORWARD A REQUEST TO FLY TO ZZZ1 IF WE COULD AND IF THE PLANE WAS FLYING NORMALLY SINCE WE DIDN'T HAVE MUCH MAINT SUPPORT IN ZZZ. FROM READING THE MSG I WOULD SAY DISPATCH DIDN'T REALLY AGREE WITH THE MSG BUT FORWARDED IT ANYWAY. AT THE POSITION WE WERE IN I THINK THE MSG WAS INAPPROPRIATE. I AM GUESSING THAT MAINT CTL (AND MAYBE DISPATCH) DIDN'T HAVE A REAL FEEL AS TO HOW SERIOUS THE SITUATION WAS AT THE TIME.CALLBACK CONVERSATION WITH RPTR REVEALED THE FOLLOWING INFO: THE REPORTER STATED THAT AS FAR AS HE KNOWS THE RUDDER AND ELEVATOR HINGE BEARINGS WERE CHANGED; THE ACFT TEST FLOWN BY ACR TEST PILOTS AND PUT BACK INTO SVC. HE KNOWS OF NO TRIGGER THAT STARTED WHAT FELT TO HIM AND THE FO LIKE UP AND DOWN FLUTTERS. THEY WERE CLBING WHEN A SLIGHT FLUTTER STARTED. IN A PERIOD OF 4-5 SECONDS IT DEVELOPED INTO A SEVERE FLUTTER. IF THE FLT ATTENDANTS IN THE BACK WERE NOT HOLDING ON TO SOMETHING THEY WOULD HAVE BEEN ON THE FLOOR. THE CREW BELIEVES THE MOTION WAS STRONGER IN THE ACFT'S AFT THAN UP FRONT. THIS ACFT HAD A MAINTENANCE WRITE UP FROM 5 DAYS PRIOR THAT RESULTED IN A FLT CREW FLUTTER CHECKLIST COMPLETION. AS FAR AS THIS CREW KNOWS THE ACFT IS BACK IN SVC.

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.