One of the wind turbines in a wind farm automatically stopped at 3:09 a.m. following a “vibration” episode. The maintenance technicians, arriving on site at 9:30 a.m. (dispatched by the wind turbine manufacturer), found a 20 m blade lying on the ground at the foot of the mast. The other 2 blades were still in place on the turbine. A 100-m safety perimeter was established around the wind turbine. A security company was contracted to monitor the perimeter and prevent intrusion by third parties. All of the machines at the wind farm were then shut down for inspection and then restarted, with the exception of the damaged wind turbine, whose blade had to be replaced. The facility operator declared the damage to its insurers that same afternoon. The portion of the blade that had become detached was removed from the site for expert analysis. At the time of the accident, the wind speed was between 18 m/s and 22 m/s.

The expert assessment identified the direct cause of the blade’s failure as follows: cracks were detected on the aluminium component referred to as the “alu ring”, located at the base of the blade. This part is essentially the connection piece between the glass-fibre blade and the metal hub. All but one of the wind turbines at the wind farm were equipped with this component. Before putting the wind farm back into service (which had been shut down following the incident), ultrasonic inspections were conducted on all the “alu ring” parts. Two turbines were maintained shut down after advanced cracking on this part was discovered.

In 2014, the wind farm operator was to replace the blades with redesigned parts. The other blades are to undergo periodic inspection to monitor the development of cracks in order to schedule, if necessary, the replacement or repair of any defective blades.