All of America's most important airlines operate what are known as hub-and-spoke networks. Airlines like Delta Air Lines, United Airlines, and American Airlines are classified as full-service-network carriers, and they primarily focus on serving business travelers and higher-end leisure travelers, with budget airlines and other non-traditional carriers seeking to target more price-sensitive travel demographics.
A core element of the legacy airline operating model is the hub-and-spoke system, which involves funneling passengers through large connecting hubs to provide as efficient access to as many destinations as possible.
For example, one of the largest and most important hub airports in the United States is Dallas/Fort Worth International Airport (DFW), which serves as the principal operational base for American Airlines, which is headquartered nearby.
From this airport, American Airlines serves a massive array of global destinations, and it uses its position at the airport to serve as a super-connector, offering passengers the ability to connect on American flights through Dallas to any of its many destinations.
However, the heavy reliance on hubs puts legacy airlines in a difficult position when it comes to scheduling flights, as they have to find a way to carefully balance their very complex schedules to offer passengers an efficient set of connections.
This, at the end of the day, is often one of the most important factors that passengers consider when deciding which carrier they are going to be flying with. While this may seem relatively unimportant, it is far more challenging than it may seem.
Airline scheduling is incredibly important
Let's take passengers looking to fly between San Antonio International Airport (SAT) and London Heathrow Airport (LHR). Currently, no airlines are offering nonstop flights between these two cities, leaving it up to legacy airlines to offer the best connecting itineraries.
If the best itinerary that American Airlines could offer passengers involved a five-hour layover in Dallas, while the airline's competitor, United Airlines, could offer an itinerary with a stop at George Bush Intercontinental Airport (IAH) in Houston of just two hours, it would be difficult for American to compete. These challenges would be even bigger for business travelers.
Therefore, airlines put immense effort into designing the most convenient flight schedules for passengers, while also balancing the need to efficiently and effectively deploy their aircraft and crew assets.
As a result, the art of scheduling flights has become somewhat of a precise science, one which often involves applied mathematicians using network flow algorithms to carefully track how best to funnel passengers through hub airports.
In this article, we will take a deeper look at exactly how airlines schedule flights at their major hubs, using American Airlines' fortress hub in Dallas as an example.
Airlines typically schedule their flights in "banks"
Early in the morning every day, flights using aircraft that have spent the night at spoke cities will make their way to the hub city. This early wave of flights is popular with business travelers who want to arrive at their destination before morning meetings take place.
Once these aircraft arrive at a hub airport, passengers whose destination is not the hub will change planes to a connecting aircraft, a process that typically takes a minimum of 45 minutes for those traveling on domestic itineraries.
While parked at a hub airport, legacy carriers will also transfer cargo between planes. This exact process can easily be observed at the American Airlines Dallas/Fort Worth hub, where hundreds of daily flights operate through many different waves of flights.
According to Gerald N. Cook and Bruce G. Bilig's 2023 book Airline Operations and Management, a wave of inbound flights from a hub is known as a bank, and the same term is also used to describe a large wave of outbound flights that arrive at a hub and head back to spoke cities.
The combination of an inbound bank and an outbound bank is known in the industry as a flight complex, and airports in the United States will often have multiple daily complexes.
At Dallas/Fort Worth International Airport, American operates multiple different daily complexes, with the earliest starting around 6:30 AM and the final departing around 10:30 PM. In total, the carrier operates 11 daily flight complexes from the airport.
Carriers have to carefully examine the order of how flights arrive at a hub
While one might instinctively think that there is no real rhyme or reason to how airlines schedule flights within a bank, there is actually a very careful formula for how airlines will choose to schedule flight arrivals and departures within a bank.
Typically, the first flights arrive from international destinations, as passengers arriving from inbound international flights will require extra time to pass through customers and immigration, in addition to baggage re-claim and security re-check. At some airports during peak times, this can take hours.
The next set of flights to arrive are regional jets. Small regional jets are operated by regional airlines that fly for larger legacy carriers as part of a sub-brand. In the case of Dallas/Fort Worth, these flights are operated by American Eagle for American Airlines.
Regional jets typically use smaller gates or remote stands to board passengers, which means that passengers arriving at these kinds of flights are likely going to be further away from the main connecting gates.
Thus, these passengers will need some extra time to transfer to connecting flights. Finally, flights from major cities will arrive, as these aircraft will be the easiest for passengers to connect between.
A deeper look at the benefits and downsides of this kind of hub schedule
The system of hubs and spokes that operate via a set of daily complexes is actually more complicated than it might initially seem. For starters, several significant drawbacks come along with the benefits of operating this kind of system.
For starters, airlines like American Airlines often have to leave their planes lying around for a few hours at a time at spoke airports to best slot a certain flight into a given aircraft bank.
This is responsible for the biggest drawback that comes along with complex banked hub schedules. Specifically, aircraft and crew are not used as efficiently as they could be.
This is one of the principal reasons why one will rarely see a low-cost airline operate banked hubs. Legacy carriers, however, tend to accept this as a necessary evil as their operations are more reliant on offering convenient connecting itineraries.
There is one way around this issue, and airlines have attempted it in the past. According to the Northwest University Transportation Center, American Airlines in the past has attempted to shift its strategy regarding banked hubs.
During the 9/11-induced decline in commercial air travel, American sought out ways to improve its operational efficiency to survive through a period of financial difficulties.
The airline attempted a strategy in which it built out "rolling" hubs or facilities which pretty much saw flights come in evenly throughout the day. This resulted in a higher rate of aircraft utilization and lower crew costs per flight, both of which ultimately helped the airline reduce the costs of the flights that it offered.
However, the benefits of using traditional banked hub systems are extensive, and in most cases, they do outweigh their drawbacks. For the most part, it is far more important that legacy airlines offer their business travelers connecting itineraries, otherwise they would be at a competitive disadvantage. The current system of banked hubs tends to support these objectives.
