Narrative:

On climbout during a ferry flight out of ZZZ where heavy maintenance had been performed; at FL310; 240kts; mach 0.70 the aircraft began a significant shudder not associated with anything obvious. We coordinated for an immediate level off and a lower altitude. Shuddering continued until approximately FL290 whereat we elected to slowly accelerate to almost 290K when the shuddering began again. We continued to lower altitudes; slowed down and eventually ended up at FL230 and approximately 260K. Shuddering was intermittent and less intense; but had no logic between airspeeds and altitudes. We discussed continuing to our destination until we determined this was periodic shuddering and could not be avoided. We coordinated with dispatch and maintenance control and elected the best course of action was a return to the maintenance base at our departure station. We performed exterior visual inspections; analyzed all systems and found no anomalies. We coordinated for a controllability check in accordance with the manual on our return. Although shuddering was still intermittent and lasted less than a minute and was spaced more than 3-5 minutes apart; no issues were found with controllability. We landed uneventfully although the captain noticed minor strange 'looseness' and nosewheel shimmy. Aircraft did yaw once to the left when we lowered gear; but at no time did we feel any problems with total control of aircraft. A thorough debrief with maintenance was conducted.

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Original NASA ASRS Text

Title: An unexplained recurring shudder in the airframe caused an A320 Flight Crew to return to their departure airport where the aircraft had just undergone heavy maintenance.

Narrative: On climbout during a ferry flight out of ZZZ where heavy maintenance had been performed; at FL310; 240kts; Mach 0.70 the aircraft began a significant shudder not associated with anything obvious. We coordinated for an immediate level off and a lower altitude. Shuddering continued until approximately FL290 whereat we elected to slowly accelerate to almost 290K when the shuddering began again. We continued to lower altitudes; slowed down and eventually ended up at FL230 and approximately 260K. Shuddering was intermittent and less intense; but had no logic between airspeeds and altitudes. We discussed continuing to our destination until we determined this was periodic shuddering and could not be avoided. We coordinated with Dispatch and Maintenance Control and elected the best course of action was a return to the maintenance base at our departure station. We performed exterior visual inspections; analyzed all systems and found no anomalies. We coordinated for a controllability check in accordance with the manual on our return. Although shuddering was still intermittent and lasted less than a minute and was spaced more than 3-5 minutes apart; no issues were found with controllability. We landed uneventfully although the Captain noticed minor strange 'looseness' and nosewheel shimmy. Aircraft did yaw once to the left when we lowered gear; but at no time did we feel any problems with total control of aircraft. A thorough debrief with maintenance was conducted.

Data retrieved from NASA's ASRS site as of April 2012 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.