Back in the mid ninetys I works with the company that does that. It is 10 two foot circular saw blades powers by a snow mobile engine, all hanging from 200 feet of 3 inch pipe, with a quick detach in an emergency. Had to refuel the chopper every hour and 45 minutes. the pilots worked ten hour days, ten days on, 21 days off . Could trim 5 miles of powerline right of way, both sides a day.