I don't know much about this, but: - I think they are fiberglass - IIRC they actually need to be locked beyond some safe maximum windspeed because the forces

I don't know much about this, but: - I think they are fiberglass - IIRC they actually need to be locked beyond some safe maximum windspeed because the forces they're under are indeed sufficient to tear them apart. I guess if local conditions can change faster than they can be locked (or if the locking systems can fail?) with any frequency, then such damage might be common. - I do also wonder if something like a bird impact is common, and whether it's enough force to crack the fiberglass (or whether reverberations of the impact on an active turbine would cause trouble)?