Airlines: (Route) Networks supported by (Computer) networks
Physically speaking, airlines are large networks whose graphs consist of the airports which they service (i.e. nodes) and the routes that they fly (i.e. edges). There are a few basic models for the physical airline networks. First is the hub-and-spoke model, in which airlines concentrate their operations in a few airports, providing feeder service to and from these hubs to connect passengers to a multitude of destinations. Flying on airlines who use the hub-and-spoke model will usually require passengers to fly to hub on one aircraft, get off, and fly on another aircraft to either another hub or their final destination. The other model that airlines may use is the point-to-point system. In this system, airlines tend to spread their operational concentration among more airports. This way, they can offer passengers with direct service to more destinations from each airport they service. However, each edge in this P2P graph may be serviced by only 1-3 flights per day, whereas in the hub-and-spoke models, each edge in the graph may be serviced with as many as 4-7 flights per day.
Supporting airline operations are very costly computer networks that manage reservations, frequent flier accounts, crew and flight schedules, aircraft and gate availability, and even provide automatic verifications with the No Fly List to ensure no one boards a plane who is not allowed to do so. Airlines have recently come under intense scrutiny for the lack of redundancies built into their computer and information networks. This past summer alone, two major airlines — Delta and Southwest — suffered computer network outages. Both circumstances required the respective airlines to halt their operations for a number of hours. When they finally, were able to get their information networks back online, it took airlines several days to finally come back to full operation, and to get the physical network properly flowing again. Airlines must be focused on their computer networks in the information age to properly succeed.
Link: http://www.bloomberg.com/news/articles/2016-08-10/delta-s-systems-failure-marks-wake-up-call-for-airline-industry