In any town of reasonable size today, the helicopter has become a common site. So familiar, that most of us go about our business unaware of its presence. In most large cities, where the rush of traffic clogs the roads as suburbanites stream to work and away from it, there is a traffic helicopter. I'm sure you wouldn't be able to identify it, and possibly, you haven't even noticed it. But you probably, at one time or another, have heard the pilot's voice...