10 km downwind from a wind turbine? i am assuming a windy day? arnt most, if not all wind turbines installed on the tops, or near the tops of hills and ridge lines?
can he be sure it was wake turbulence? or a rotor generated by terrain?
i have even been rolled onto my back at 85ooft on a clear sunny day with no aircraft within miles, and terrain 83oo ft below me, was it wake turb?