Concrete tower parts of concrete-steel hybrid towers of wind turbines can show abnormalities in the material a few years after construction. Initially small cracks and spalling can later lead to critical damage in the concrete structure.That is why it is important to assess any anomalies on the tower before the end of the warranty period so that they can be repaired. In a pilot project for a European wind turbine manufacturer, TÜV Nord is using drone support for the end-of-warranty inspection. The entire concrete tower is photographed by drone. TÜV Nord employees evaluate the images afterwards. In the medium term, an automated image recognition system is also to be used. Using the drone-based inspection, 34 of the manufacturer's wind turbines have already been assessed this year. Now, the procedure is being extended to additional sites.