In a farm of 26 wind turbines of 2 MW operational since 2008, an aerogenerator was taken offline around 3 am after detecting abnormal oscillations. At 8 am, the on-call maintenance crew noted that a blade had fallen (9 tonnes, 46 m) at the base of the installation, along with a break in the bearing connecting the blade to the hub. The mast foot was located 190 m from the D389 road and 400 m from the A10 motorway.

An analysis of sensor recordings and maintenance reports did not reveal any anomaly or precursor (abnormal stresses capable of damaging the bearing, suspicious vibration before the break, blade direction deviation, visual defects at inspections, etc.). Traces of corrosion were detected in the boring holes crossing one of the bearing rings connecting blade to hub. According to the manufacturer, this corrosion stemmed from the conditions for producing and storing bearing components. The aerogenerator was restarted at the end of October after replacing the damaged blade and installing new, corrosion-resistant bearings.

The wind farm operator requested the turbine maintenance subcontractor and manufacturer to:

• proceed with a visual inspection of the bearings on all wind turbines every 3 months;
• perform an acoustic control of the bearings and measure the level of corrosion;
• remove corrosion from borings most at risk;
• verify the absence of residual cracks due to eddy currents.