A hub airport is a central airport where one or more airlines concentrate their flights, routing passengers through it to connect them to dozens or even hundreds of other destinations. Think of it like the center of a bicycle wheel: flights radiate outward like spokes, and passengers traveling between two smaller cities often connect through the hub rather than flying direct. This system shapes how most of the world’s major airlines operate today.
How the Hub-and-Spoke System Works
Without hubs, an airline would need to offer direct flights between every pair of cities it serves. For 20 cities, that means 190 separate routes. A hub collapses that math dramatically. Instead, the airline flies each city into one central airport, and passengers switch planes there. Those same 20 cities now need only 19 routes, all funneling through the hub.
In practice, this means airlines schedule waves of arriving flights followed by waves of departures. You land at the hub, walk to your connecting gate during that window, and board a flight heading to your final destination. Major U.S. carriers like American, Delta, and United each operate multiple hubs spread across the country, giving them broad geographic reach and letting passengers connect through whichever hub offers the most convenient routing.
Why Airlines Use Hubs
The hub model exists because it lets airlines fill more seats on every flight. A plane from a mid-sized city to a hub carries not just passengers going to that hub city, but also travelers connecting onward to 50 or 100 other places. That pooling of demand means fuller planes and, ultimately, lower costs per passenger. Research from Duke University found that airlines with more concentrated hub operations have lower costs per passenger mile and lower overall operating expenses, largely because consolidating flights at one airport lets them use bigger, more fuel-efficient aircraft carrying more people per trip.
The tradeoff is real, though. Running a hub is expensive on a per-seat basis because of the infrastructure, staffing, and gate space required to coordinate those connection waves. The financial advantage only kicks in when the airline fills enough of those seats with connecting passengers to offset the higher overhead.
Origins in Airline Deregulation
Hub airports as we know them are a product of the late 1970s. Before 1978, the U.S. government controlled which routes airlines could fly and what fares they could charge. When Congress passed deregulation legislation that year, airlines suddenly had the freedom to design their own networks. Most quickly gravitated toward the hub-and-spoke model as the most efficient way to serve a large number of cities.
PeoplExpress, one of the first airlines born after deregulation, made the underused Newark, New Jersey, airport its hub when it launched in 1981. Larger carriers followed the same logic on a bigger scale, turning cities like Dallas, Chicago, and Atlanta into massive connecting points that still dominate air travel today.
Fortress Hubs, Secondary Hubs, and Focus Cities
Not all hubs are created equal, and the industry uses a few specific terms to describe the differences.
- Fortress hub: An airport where a single airline so thoroughly dominates the market that competitors struggle to gain a foothold. Think of Delta in Atlanta or United in Houston. The dominant carrier controls most of the gates, commands the highest share of flights, and often has significant pricing power on routes through that airport.
- Secondary hub: When an airline’s primary hub hits capacity limits, it opens additional hubs to expand its network. Operating multiple hubs lets an airline cover more geography and offer passengers connections through different cities, creating more possible itineraries.
- Focus city: A destination where an airline runs a limited set of point-to-point routes, primarily serving the local market rather than funneling connecting passengers. It looks like a small hub but functions differently because the airline isn’t building connection waves there.
The World’s Most Connected Hubs
OAG, an aviation data firm, ranks the world’s most connected airports each year based on the number of scheduled connections and destinations served. For 2025, the top five global megahubs are:
- London Heathrow (dominant carrier: British Airways)
- Istanbul Airport (dominant carrier: Turkish Airlines)
- Amsterdam Schiphol (dominant carrier: KLM)
- Kuala Lumpur International (dominant carrier: AirAsia)
- Frankfurt International (dominant carrier: Lufthansa)
Geography plays a huge role in these rankings. Istanbul and Kuala Lumpur sit at natural crossroads between continents, making them ideal places to connect flights between Europe, Asia, and beyond. Heathrow and Amsterdam benefit from being gateway airports for transatlantic and European traffic, with airlines that have built decades of connecting infrastructure around them.
Hub-and-Spoke vs. Point-to-Point
The hub model isn’t the only way to run an airline. Low-cost carriers like Frontier and Spirit typically use a point-to-point model, flying passengers directly between city pairs (often medium-sized markets the big airlines overlook) without routing them through a central hub. This avoids the complexity and cost of coordinating connection waves but limits the number of destinations the airline can profitably serve.
The tension between these two models shaped the aircraft industry itself. Airbus bet on the hub future by building the enormous A380, designed to carry huge numbers of passengers between mega-hubs. Boeing bet on point-to-point by developing the 787 Dreamliner, a smaller, fuel-efficient plane that could fly long distances between mid-sized cities. The 787 became one of the best-selling widebody jets in history. The A380 was discontinued in 2021. Newer aircraft like the Airbus A321XLR and A350 continue to make long-haul point-to-point routes viable with lower capacity and better fuel economy.
In reality, most major airlines blend both approaches. American, Delta, and United all operate hub-and-spoke networks but also run plenty of direct routes between popular city pairs. The pure hub model and the pure point-to-point model are endpoints on a spectrum, and most carriers sit somewhere in between.
What Hubs Mean for Travelers
If you’re booking a flight, the hub system affects your experience in a few concrete ways. Flights through a hub city are often cheaper than nonstop alternatives because the airline can fill those planes with passengers going to many different places. The downside is the layover: you’re adding time, a connection, and the risk of a missed flight if the first leg runs late.
Flying out of a hub city is generally an advantage. You’ll have more nonstop options, more competition on popular routes, and more flight times to choose from. Flying out of a smaller spoke city means most of your trips will route through a hub, adding 1 to 3 hours of travel time depending on the connection.
Fortress hubs can cut both ways. You get excellent connectivity and frequent flights, but with one airline controlling the market, fares on routes through that hub tend to run higher than at airports with more competition. If your home airport is a fortress hub, joining that airline’s frequent flyer program usually makes the most practical sense since they’ll dominate your options.