A system for a wind park including: a control system in communication with a plurality of unmanned air vehicles, wherein the control system is configured to deploy one or more unmanned air vehicles during a triggering condition; and wherein the deployed unmanned air vehicles are guided towards an assigned wind turbine and to interact with a blade of that wind turbine in order to control oscillation of the blade. The invention also embraces a method for reducing blade oscillations of a wind turbine, comprising: monitoring for a triggering condition associated with the wind turbine; on detecting the triggering condition, deploying unmanned air vehicles towards a wind turbine and interacting with a blade of the wind turbine using the unmanned air to control oscillation of the blade. The invention therefore provides an efficient approach to controlling blade oscillations with minimal human operator involvement. Drones may be deployed automatically once suitable conditions are detected and may automatically engage with the blades, either by contacting those blades physically, or by interacting with the blades in close proximity, in order to disrupt airflow around the blades thereby reducing oscillations.