Loss of control and a lack of training is to blame for a fatal helicopter crash during protests of a white nationalist rally in Charlottesville nearly three years ago, the National Transportation Safety Board said in a final report.

The 13-page report issued Wednesday noted the pilot's loss of control after the Virginia State Police helicopter had lost lift as well as his lack of training in how to recognize such a problem and how to help the aircraft recover from it.

The crash near Charlottesville on Aug. 12, 2017, killed 48-year-old state police Lt. H. Jay Cullen and 40-year-old trooper-pilot Berke M.M. Bates. They were conducting surveillance of a Unite the Right rally.

The loss of lift is known as "vortex ring state." Online websites say it causes a helicopter to lose main rotor lift and experience loss of control.

According to the NTSB report, the state patrol training manual said vortex ring state was not listed in any of the sample lesson plans for initial or recurrent training. Additional information showed the pilot had knowledge of vortex ring state, but a review of his training records from 2001 to the time of the accident found "no record of him receiving settling with power or vortex ring state recognition and recovery training on the accident helicopter make and model."