Event Description
A Dornier 328-300 aircraft experienced uncommanded rudder oscillations while descending. At the onset of the oscillations, the autopilot was engaged. The flight crew disengaged the autopilot, but the oscillations continued unabated.
Maintenance Action
Following the event, maintenance personnel replaced the integrated avionics computer (IAC). The aircraft subsequently underwent a maintenance test flight, during which no anomalies were observed. The airplane was then returned to service.
Investigation Findings
Examination of the removed IAC revealed no direct link between the unit and the rudder oscillations. As of seven months after the incident, the uncommanded rudder oscillations have not recurred on the aircraft.
Conclusion
The cause of the rudder oscillations was not determined.