A bird's nest lodged in the ventilation duct of a 300 kW Bonus wind turbine was the cause of the machine's major failure at the end of March (Windpower Monthly, May 1994). According to a provisional report from the Wind Turbine Test Centre at Risø, the generator overheated causing the wind turbine to automatically stop. But while at a standstill, lightning struck the rotor, destroying two of three air brakes at each blade tip. Once the generator had cooled, the wind turbine started again, but with only one brake in working order the rotor was unbalanced and overspeeded. The tower eventually gave way at its weakest point.