Fortress hub

Airline hubs or hub airports are used by one or more airliners to concentrate passenger traffic and flight operations at a given airport. They serve as transfer (or stop-over) points to get passengers to their final destination. It is part of the hub-and-spoke system. An airline operates flights from several non-hub (spoke) cities to the hub airport, and passengers traveling between spoke cities need to connect through the hub. This paradigm creates economies of scale that allow an airline to serve (via an intermediate connection) city-pairs that could otherwise not be economically served on a non-stop basis. This system contrasts with the point-to-point model, in which there are no hubs and nonstop flights are instead offered between spoke cities. Hub airports also serve origin and destination (O&D) traffic.

The hub-and-spoke system allows an airline to serve fewer routes, so fewer aircraft are needed. The system also increases passenger loads; a flight from a hub to a spoke carries not just passengers originating at the hub, but also passengers originating at multiple spoke cities. However, the system is costly. Additional employees and facilities are needed to cater to connecting passengers. To serve spoke cities of varying populations and demand, an airline requires several aircraft types, and specific training and equipment are necessary for each type. In addition, airlines may experience capacity constraints as they expand at their hub airports.

For the passenger, the hub-and-spoke system offers one-stop air service to a wide array of destinations. However, having to regularly make connections en route to their final destination increases travel time. Additionally, airlines can come to monopolise their hubs, allowing them to freely increase fares.

Airlines may operate banks of flights at their hubs, in which several flights arrive and depart within short periods of time. The banks may be known as "peaks" of activity at the hubs and the non-banks as "valleys". Banking allows for short connection times for passengers. However, an airline must assemble a large number of resources to cater to the influx of flights during a bank, and having several aircraft on the ground at the same time can lead to congestion and delays. In addition, banking could result in inefficient aircraft utilisation, with aircraft waiting at spoke cities for the next bank.

Instead, some airlines have debanked their hubs, introducing a "rolling hub" in which flight arrivals and departures are spread throughout the day. This phenomenon is also known as "depeaking". While costs may decrease, connection times are longer at a rolling hub.American Airlines was the first to depeak its hubs, trying to improve profitability following the September 11 attacks. It rebanked its hubs in 2015, however, feeling the gain in connecting passengers would outweigh the rise in costs.

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Wikipedia