I haven't operated into them, however have been to them on skiing trips and the like. As I understand it, the sand is spread on the snow - which is packed solid, more like solid ice than snow, and the sand is pressed into that surface to provide traction. From the areas I have walked on and examined (hey - I was curious!) I don't think ingestion would be a big issue, unless the sand had just been laid. Following normal procedures of making sure of idle reverse below 60 knots would take care of most of it, I would think. Norwegians I have spoken to say it's not much of an issue - feels more like concrete than snow! I have operated in blowing sand in Australia, and that would probably have been worse for the engines.