At most airports, responsibility of air traffic control starts and stops at the entrance or exit to the runway movement areas, which are taxiways and runways. In the non-movement areas, such as hangers, ramps, and aprons, aircraft movements and separation are no longer the responsibility of air traffic...http://www.google.ca/patents/US7667647?utm_source=gb-gplus-sharePatent US7667647 - Extension of aircraft tracking and positive identification from movement areas into non-movement areas
