What are Airport scan requests?
The scan requests are the system (the airportd dameon) scanning for available WiFi networks. In reviewing the log, it seems to do it in earnest for a minute, then slow down for several minutes, then pick back up. I'm not sure why it is doing it so often, but as long as your battery life does not seem to be suffering and the system is not slowing during these periods, I wouldn't worry about it.