The only US Army helo with heated main blades is the Black Hawk, unless I have missed something recent. The system is a de-ice system, as it allows a thin skim of ice to build up, then rapidly heats the leading edge to disbond it and allow it to sling off with the centrifugal force. The heat is timed to toss the ice away from the tail rotor (which is also heated).
All US Army helicopters have anti-ice heated bellmouth inlets, which are continuously heated so no ice forms at all.
The Hawk is cleared into moderate ice, with a max Liquid Water Content of 1 Gm/M3. I know of no such permission for Apaches, Chinooks or the OH-58 family.
The entire Russian fleet is de-iced, for obvious reasons! So are many H-3's.
News from operators would be welcomed here.
[ 10 November 2001: Message edited by: Nick Lappos ]