This week Trivik Verma from ETH Zurich and a few colleges published a study of the vulnerability of the world airlines network, and the conclusion they got is unexpected: the core of the network is really robust, but the periphery of the network is formed by a network of airports connected to single hubs. Closing one of this hubs would result in huge regions getting inaccessible.
The global network is formed by 3237 airports, connected between them by 18 000 routes. The core of the network is formed by 73 airports that are connected to each other by more than 400 groups of three routes – if any of this airports is closed, goes offline for any reason, several alternative routes will be still available. Most of this airports are in Europe and North America.
But as you get further away from this central nodes, there are big regions where several airports are connected to a single airport, with no alternative routes. This is a consequence of the small size of the markets they serve and the need the airlines have to maximize profit, while at the same time minimize flying time.
See more at MIT Technology Review website