In general, we can distinguish between two business models used by airlines around the world:

• the use of a hub (airport) where passengers transfer to another aircraft and continue their journey to their destination. This model is known as Hub and Spoke. Example: Zagreb–Frankfurt–Copenhagen, where the passenger first travels on a Zagreb–Frankfurt flight and then transfers in Frankfurt to another flight to Copenhagen.

• a direct flight between two destinations. Example: Zagreb–Copenhagen, where the passenger flies to their destination without changing aircraft or making a connection. This model is known as Point to Point.

Although hybrid systems—in which airlines use both models—do exist, most airlines generally opt for only one of them. Airlines operating through hubs include KLM, Lufthansa, Air France, Singapore Airlines and Emirates, while airlines operating only direct flights without offering connections include Ryanair, Wizz Air, easyJet and others—primarily low-cost carriers.

Flying via a hub

You need to travel—for example, you are going on a business trip to Bilbao. You live in Zagreb and, naturally, the first thing you will check is whether there is a direct flight from Zagreb to Bilbao. Unfortunately, there is not. Nor is there a direct flight from Zagreb to a nearby airport in the Bilbao area from which you could reach your meeting by public or organised transport. There is a flight to Madrid, but the distance between Madrid and Bilbao is approximately 400 kilometres, requiring around four hours of driving. Barcelona is even farther away, leaving you with a journey of 600 kilometres or almost six hours by car. This is only an option if you have plenty of time, but because time is usually quite limited on business trips, you cannot afford to spend an entire day travelling. The same applies to travelling from a nearby airport such as Venice, which has a direct flight to Bilbao. Once the journey from Zagreb to Venice and the requirement to arrive two hours before departure are taken into account, you will again spend around six hours travelling.

This is where travelling through a European hub comes into the picture—we are focusing on Europe in this article, although the same principle applies anywhere in the world—allowing you to reach your destination with a connection. You can therefore travel from Zagreb to Frankfurt or Amsterdam, for example, and transfer at one of those airports to a flight to your final destination: Bilbao.

Naturally, in most cases, such a ticket will cost more than a direct flight operated by a low-cost carrier, but it will save you time. There is always a balance to be struck between saving time and saving money, as everyone has their own priorities and preferences. Business travellers will want to spend as little time as possible travelling and adjust their flights to their meeting schedules, while tourists will generally focus on price and prefer adapting to the schedules of low-cost carriers rather than paying more for a journey through a hub. Nevertheless, with a connection, you can reach Bilbao in approximately five hours, which is roughly equivalent to the driving time between Madrid and Bilbao or Zagreb and Venice. The cost of a direct flight must also include the price of renting a car or the expenses associated with using your own vehicle, such as fuel, tolls and parking. These indirect costs can sometimes be considerable, making it necessary to determine whether travelling directly or with a connection is more worthwhile.

Since Ryanair has arrived in Zagreb, it is now possible to combine one of its flights to Milan, for example, with another Ryanair flight or a flight operated by another airline to the final destination. However, this creates the problem of an unprotected connection, under which passengers personally assume considerable risk. If your flight from Zagreb to Milan is delayed because of weather conditions, for example, and you consequently miss your flight from Milan to Bilbao, your ticket to Bilbao will unfortunately become invalid because you have failed to meet one of the conditions of carriage: appearing at the boarding gate at the specified time. In such a case, you will not receive compensation for the delay to the first flight because it was caused by extraordinary circumstances, while you will also have to purchase a new ticket to your final destination and potentially cover additional accommodation costs. Such a journey may be inexpensive, but it can also be challenging.

Flying through a hub offers airlines several advantages

Flying with a traditional airline such as Lufthansa or KLM means that your journey to the final destination is protected. In the event of a delay, the airline will take care of you, transfer you to the next available flight or pay for accommodation until the following flight. For example, you may depart from Zagreb for Frankfurt on a morning flight, only for that particular service to be cancelled for some reason. However, because several other flights to Frankfurt operate that day, you will most likely be transferred to the next flight with an available seat. Ultimately, this means you will probably still reach your destination on the same day. Airlines operating hubs—or, even better, several hubs—have greater flexibility in the event of operational disruptions and can reroute passengers using another partner airline. If you are travelling with Lufthansa from Zagreb to Copenhagen via Frankfurt and reach Frankfurt only to discover that the Copenhagen flight has been cancelled, you may be rerouted via Munich or transferred to an Austrian Airlines service from Frankfurt to Copenhagen via Vienna, or a SWISS service via Zurich.

With a low-cost carrier, if your flight is cancelled that day, you will most likely be unable to travel to your destination until the following day or even several days later, particularly if the route operates only two or three times per week.

When travelling with an airline operating through a hub, you can often select a flight that suits you better—for example, one departing in the morning or perhaps in the early evening, depending on your needs. Airlines operating only direct flights generally do not offer such a broad selection. Their schedules may be limited to one daily flight or only several flights per week, meaning you cannot choose the departure time but must accept the only available flight, regardless of whether it suits you. Flexibility is therefore limited. This is particularly inconvenient for business travellers who need to attend meetings during the day and depart on a flight later in the evening. Even on leisure trips, when returning home, the latest possible flight on the final day of a holiday is often the most convenient, allowing travellers to sleep in that morning and perhaps visit one more attraction before departing.

Disadvantages of flying through a hub / advantages of flying directly

A hub needs at least one daily flight to each destination to provide connectivity, while several daily flights are required to improve connections and reduce passenger waiting times at the hub. Ultimately, this means that smaller aircraft, such as the Dash 8-Q400 or Embraer E175, with around 70 seats, are required in the fleet for destinations that do not generate large passenger volumes. This makes it possible to maintain a higher number of daily frequencies while keeping total daily capacity low enough to avoid flying with too many empty seats.

However, this also creates a disadvantage because airlines must operate aircraft of different sizes. Cities generating higher passenger volumes may require around 200 seats per flight, meaning that an aircraft such as the Airbus A321 will be needed. A diverse fleet also requires pilots to be assigned to individual aircraft types, as the same pilot cannot fly an Embraer in the morning and an Airbus in the afternoon. Airlines also need mechanics trained to maintain several aircraft types and must hold a larger inventory of spare parts. Fleet maintenance and planning consequently become more complicated and more expensive.

By contrast, most low-cost carriers operate highly standardised fleets, reducing pilot costs because all their pilots can fly every aircraft in the fleet while also simplifying maintenance. Austrian Airlines, for example, operates Embraer E195, Airbus A319, Airbus A320 and Airbus A321 aircraft on short- and medium-haul routes. Until recently, it also operated the Dash 8-Q400. It therefore had five aircraft variants and pilots trained for three different aircraft types. Ryanair, meanwhile, operates only Boeing 737-800 aircraft and has begun renewing its fleet with the 737 MAX.

Airlines whose operations are based around a hub are tied to that hub and have less flexibility to redistribute capacity to other bases. Low-cost carriers are considerably more flexible in this respect. Consider Lufthansa and Ryanair: Lufthansa operates hubs in Frankfurt and Munich and, with a few exceptions, organises all its flights to and from those two airports. At most, it can redistribute capacity between the two hubs.

Ryanair, meanwhile, moves its capacity—or aircraft—to locations where demand exists. It may have ten aircraft based at one airport, but if demand no longer justifies that level of capacity, it can move two aircraft to Zagreb and another three to a different airport, leaving only five aircraft at the original base. If demand increases the following year, additional aircraft can be returned. If demand decreases, they can be moved elsewhere. This allows Ryanair to open and close bases very quickly. Such flexibility enables it to position itself in markets where it can fill almost 100% of the seats on its aircraft, which is one of its principal strengths and competitive advantages. Nevertheless, moving aircraft between bases also requires considerable effort because each base must be organised, new employees hired, maintenance support arranged and pilots and cabin crew relocated.

Time is another important factor because flights at hubs are generally organised in waves. A large number of flights arrive in Amsterdam at approximately 8 a.m., while numerous departures take place between 9 and 10 a.m. During this one- or two-hour period, passengers make their connections and continue to their final destinations. Put simply, a wave can be defined as the arrival and departure of a large number of aircraft belonging to the same airline within a relatively short period. This occurs several times per day at hub airports.

During these one- or two-hour gaps, aircraft usually remain on the ground waiting for their next departure, effectively “losing” time. Most low-cost carriers do not offer connecting itineraries and therefore do not need to organise flight waves. Their aircraft generally remain on the ground for only around 30 minutes before the next flight—just enough time to disembark and board passengers, refuel and depart again. Consequently, when comparing similar flights operated by similar aircraft, low-cost carriers can complete more flights and generate more daily flying hours than traditional airlines.

A major advantage of a hub is that passenger demand between Zagreb and Frankfurt, for example, may amount to only 30 passengers per day, but the Frankfurt-bound aircraft will also be filled by passengers connecting to destinations such as Stockholm, Moscow, Dublin, New York, Tokyo and Singapore. The strength of a hub lies precisely in its ability to provide connectivity to “small” destinations and link those destinations with locations throughout Europe and the rest of the world with only one connection—or sometimes several.

Many airlines base most of their business on carrying passengers from point A to point B through their hubs. Emirates is one example. Its hub-based operating model also contributed to the development of Dubai itself, transforming it from a small desert settlement into a global metropolis containing the world’s tallest building. Singapore Airlines, Qatar Airways, Gulf Air, Cathay Pacific, Etihad and Copa Airlines are further examples.

Most of these airlines grew precisely because they enabled passengers to travel between different parts of the world through their hubs. Without connecting passengers, they would have remained relatively small airlines because their home hubs do not generate enough passengers whose final destination is the hub city itself. Qatar Airways is a good example: its Doha hub does not attract an exceptionally large number of tourists, while the city itself does not generate enormous passenger volumes. If Qatar Airways operated only direct services without offering connections, it would require only a fraction of its current fleet.

Feeder

A hub needs an airline that will “feed” it with passengers and “distribute” them to their final destinations. In most cases, the airline operating the hub carries passengers using its own aircraft, although some destinations may be partially or entirely served by partner airlines.

One example is Lufthansa’s Frankfurt hub. There are five daily flights between Frankfurt and Zagreb, three operated by Croatia Airlines and two by Lufthansa. The two airlines have a codeshare agreement under which both sell tickets for their own and their partner’s flights, allowing passengers to choose whichever service suits them best. The advantage for passengers is that such cooperation provides more daily flights and a greater range of travel options.

Airlines belonging to alliances such as oneworld or Star Alliance encourage passengers to connect with partner airlines at their own hubs or those operated by their partners. Croatia Airlines is a member of Star Alliance and connects Zagreb and its other destinations with European Star Alliance hubs such as Frankfurt, Zurich, Munich and Copenhagen.

Singapore Airlines, which is also a Star Alliance member but does not fly to Zagreb, provides another example. To include Zagreb in its network of destinations, it established a partnership with Croatia Airlines, under which Croatia Airlines carries Singapore Airlines passengers to final destinations such as Zagreb, Split and Dubrovnik.

Long-haul flights

Wide-body aircraft are most commonly used on intercontinental or long-haul flights. They generally have at least 200 to 250 seats, while their capacity can exceed 600 seats in the case of the Airbus A380. Such aircraft offer considerable range but are also expensive to operate, meaning that they must achieve high load factors to generate revenue.

Cargo transport is naturally also important on long-haul flights because it generates substantial revenue, but we will leave that topic aside for now. When operating these aircraft, airlines must focus on connecting cities with a high level of potential passenger demand. This generally means linking major global cities, large hubs or popular tourist destinations if they are to fill nearly every seat.

Connecting smaller and less attractive cities carries considerable risk because airlines are unlikely to fill the aircraft. This is where hub operations become particularly important, as passengers can connect at either end of the route and continue to their final destinations.

Consider United Airlines’ new New York/Newark–Dubrovnik service. Passengers connecting at Newark have numerous possible destinations throughout the United States, while passengers arriving in Dubrovnik can also transfer to a flight to Zagreb. This increases the number of destinations effectively connected by the route.

Naturally, some passengers will need to make one or two connections, but they will still be able to travel between cities that are unlikely ever to be connected by a direct flight. One example would be Nashville–Newark–Dubrovnik–Zagreb. We can say with a high degree of certainty that a direct flight from Nashville to Zagreb is unlikely to be launched, perhaps ever or at least within the next 10 to 20 years. A passenger travelling between the two cities will therefore have to use a hub. Hubs are consequently the only realistic way to connect smaller destinations located on different continents.

Norwegian attempted to use narrow-body aircraft on transatlantic services connecting smaller airports in the United States, but unfortunately failed in its attempt and eventually discontinued its long-haul operations. Low-cost carriers followed a similar model when they first expanded in Europe, connecting secondary airports and avoiding larger ones.

However, they are now increasingly turning towards major airports because these are generally much closer to city centres, reducing travel time to and from the airport and making low-cost carriers more attractive to business travellers. Nevertheless, long-haul services that are not linked to at least one hub have not yet become widespread.

To ensure that major cities and hubs are not almost exclusively the only destinations capable of supporting long-haul flights, narrow-body aircraft such as the Boeing 757 and, today, the Airbus A321neo have entered the market. The Airbus A321XLR is particularly significant because it will provide a range exceeding 8,000 kilometres, allowing airlines to connect distant cities without requiring large wide-body aircraft.

This will allow airlines to open new routes with less risk and subsequently introduce wide-body aircraft if demand increases. The Airbus A321XLR will enable an increasing number of cities around the world to be connected. Over the next several years, we will see how this market develops, particularly on transatlantic routes. The fact that more than 450 A321XLR aircraft have been ordered demonstrates the considerable potential of this segment.

Twenty years ago, discussions about long-haul aviation largely revolved around connecting major hubs. This was one of the reasons behind the development of the Airbus A380, while the Boeing 747 also achieved excellent sales. The arrival of smaller twin-engine aircraft with fewer restrictions concerning ocean crossings and distances from suitable diversion airports—such as the Boeing 767 and 777 and Airbus A330—made it possible to connect smaller airports as well.

The introduction of the Boeing 787 and Airbus A350 further reduced the need to operate through hubs because these aircraft, particularly the 787, are smaller, more economical and offer lower capacity.

We can once again mention Emirates, whose business model is based on long-haul operations connecting Europe, Asia, Africa, the Americas and Australia through its Dubai hub. Emirates successfully changed global passenger flows, while Dubai became one of the world’s most important hubs.

Its fleet has traditionally been based on large long-haul aircraft such as the Boeing 777 and Airbus A380. However, the airline ultimately recognised the need for smaller aircraft as well and will therefore also operate the Boeing 787 and Airbus A350.

Conclusion

There is no universal answer to the question of whether flying through a hub or travelling on a direct flight is better. From an environmental perspective, direct flights are certainly the better option because the direct route is the shortest possible one, while travelling through a hub often adds a considerable number of kilometres.

For example, when travelling to Bilbao via Frankfurt, the total distance flown is approximately 1,900 kilometres, while the direct distance is around 1,500 kilometres. Flying through a hub therefore increases the distance travelled.

From a ticket-price perspective, direct travel between two destinations is usually the least expensive option, at least when flying with low-cost carriers. However, without hubs, smaller airports would lose connectivity. We can again use Zagreb and Bilbao as an example, as well as connections to long-haul flights.

If you wanted to travel to Los Angeles and hub operations did not exist, you would somehow need to reach at least Munich to access an airport offering a direct flight. Sydney would present an even greater challenge, as the nearest airport offering a direct flight to Sydney would be Dubai, for example—excluding British Airways’ London–Singapore–Sydney service.

The integration of different modes of transport, particularly rail, is again not a viable alternative, at least not in our part of Europe, because journeys by train are often measured in days. Such integration may work in Germany, France and other countries with developed high-speed railway networks, where rail travel over certain distances can be faster than flying once the journey to the airport and pre-flight procedures are taken into account.

In Germany, Lufthansa integrates its services with the high-speed railway network, while Air France does the same in France. Many other examples exist around the world. However, this makes sense only in regions with highly developed railway systems, frequent departures and excellent infrastructure. When there are only several departures per day and trains operate at low speeds, such integration simply does not make sense.

Imagine how long it would take to travel by rail from Zagreb to Skopje, Bucharest or Kyiv, while all these destinations can be reached in only several hours by flying, even with a connection. In Croatia, rail transport from Zagreb could potentially be integrated with nearby cities such as Krapina, Bjelovar, Varaždin or Koprivnica, but extending such integration much farther would be considerably more difficult. The same applies to Croatia’s other airports.

During the worst period of the coronavirus pandemic, we saw that flying through a hub was the only model that continued to function, at least in Croatia’s case. Zagreb maintained a single flight to Frankfurt, from where passengers could continue to destinations around the world. That flight was Croatia’s only connection with the rest of the world; there were no other options.

At that time, Ryanair, Wizz Air, easyJet and other low-cost carriers grounded almost their entire fleets and stopped operating. Direct flying was therefore not viable during the pandemic because passenger demand simply did not exist. The only model that continued to work was flying through hubs.

We will continue to travel both through hubs and on direct flights. Hub operations will not disappear, although they will most likely decline. Europe may eventually be left with only its largest hubs, such as Paris, Frankfurt, Munich and Amsterdam, along with several smaller hubs that also support long-haul services.

It remains to be seen whether Zagreb will manage to survive as a hub. Over the next several years, the situation will become clearer, revealing which hubs will survive and which will become airports served exclusively by direct flights.