One of the media reports said the Pilots could move the Collective Lever in full range of motion....from down stop to top stop...without any reaction from the Rotor System.
If that is true....then there must have been something that happened to sever the mechanical linkage for the Collective.....arcing from a chafed wired bundle.....fire?
If you lose collective control....two ways of changing the amount of lift being produced.....speed or Nr.....or perhaps as in this incident....speed and Nr.