It’s not often that wind turbines malfunction to the point of destruction. Recently it happened twice in the same week.

According to the Copenhagen Post, in late October in Esbjerg, Denmark, a defective axle caused a 120-foot turbine to throw off all of its blades with one slamming into a power transformer. This was followed by an incident Nov. 2 in southwestern Sweden when another turbine — this time one from Vestas — threw off a blade that landed on a hiking trail.

Two Vestas in the U.K. also reportedly failed within weeks of each other in late 2007 and two more apparently failed in Denmark in early 2008.

Since 2000, there have been only 27 incidents in Denmark of turbine blades coming loose. However, as the rate of construction increases dramatically for this source of clean power, the frequency of turbine inspections is also coming under scrutiny. Denmark recently passed a law this year requiring inspections to take place at least once a year; and the wind turbine industry in Sweden has now proposed setting up a commission to investigate incidents.

Note: Video above is from a turbine that malfunctioned in Denmark in early 2008. The turbine was not designed to spin this rapidly, and the rapid spinning indicates a probable brake failure.