The US Forest Service, uses the term to discribe a fire line crew, taken by helo, to the fire line. Fire line crew is used to bulid fire breaks, clear brush from a hill side. Generaly on the flank of a fire not in front of one. Using Helitac crews put line personell on the fire line faster then a ground driven crew can arrive, minutes instead of hours. It's also use to put crews in to remote locations that might take a long time to 'hike' into.
If that helps. A picture of these would be nice to see, Fire fighting helicopters is what I like to make.