## 2 Theoretical Background  
From the very beginning, the business model of low-cost carriers has been based on different principles than traditional full-service network carriers, with an emphasis on reducing costs to enable the lowest prices in target markets. The evolution of the low-cost model in Europe took at least a decade longer than in the USA, as the first low-cost carriers only emerged after the completion of a liberalization process that took place in several stages, starting in the late 1980s and lasting until the mid-1990s. The Irish company Ryanair was the first low-cost carrier in Europe to fully implement a business model resembling that of Southwest Airlines in the USA. As the European air transport market has developed in parallel with the economic and political enlargement of the EU, new low-cost carriers have also emerged [8]. The cost-cutting business model of low-cost carriers typically uses newer, more homogeneous, mid-sized fleets (typically the Boeing 737-700/800 or Airbus 319/320). This results in lower fuel, maintenance, and personnel training costs, as well as savings in capital investment for larger aircraft orders. Dense seating configurations contribute to greater flight efficiency and cost savings. Low-cost carriers operate point-to-point flights from smaller, less congested airports, avoiding transfers. Maximizing daily block hours results in better aircraft efficiency. Smaller airports used by low-cost carriers typically charge lower fees and are often willing to co-finance the promotion of new routes, which further reduces costs. Direct ticket sales via the internet, without intermediaries or agencies, are another characteristic of this business model. Unlike traditional full-service network carriers (FS-NCs), low-cost carriers (LCCs) provide only basic transportation services, without luxury or comfort. This includes higher seat density and the elimination of free in-flight food and beverage services, entertainment, and magazines, online check-in, mobile applications, priority boarding, etc. [9]. LC airlines apply restrictive policies regarding seat selection and hand baggage, all with the aim of reducing basic costs and increasing revenue from additional services. It is important for passengers to be well informed before making a decision to buy a flight ticket in order to avoid unexpected costs. For example, some airlines include only a small handbag in the price of the basic ticket, while any additional baggage, regardless of type, is charged additionally. Others encourage passengers to check in online instead of at the airport, which reduces staff and administrative costs. If a passenger decides to check in at the airport, the airline charges additionally for this service. Also, one of the services offered by LCCs in the additional services segment is priority boarding. It offers passengers the opportunity to board the aircraft first (before the rest of the passengers) and to secure a place for hand baggage or a better seat on the aircraft. However, it is important to point out that most passengers opt for the basic check-in and boarding option. To be considered a low-cost carrier, a company must meet the following minimum requirements: a homogeneous fleet of aircraft composed of one type of aircraft (more than 75%), the use of secondary airports (more than 50%), a point-to-point flight network without code-sharing, one-way fares, a single passenger class, and the absence of additional services during the flight. Low-cost carriers are highly adaptable to market conditions. They are also characterized by high flight frequencies (maximum aircraft utilization), short turnaround times (up to 25 min), lower labor costs, flexibility in human resource planning, and a smaller number of administrative staff [10]. The emphasis is on efficiency and simplicity, often avoiding amenities such as in-flight entertainment and complex seating arrangements. LCC aircraft spend less time on the ground, which allows for higher flight frequencies and better resource utilization.