## 2 Theoretical Background
In simple terms, customer satisfaction is expressed as a link between expectations and perception. It occurs when the perception of the performance of a certain service exceeds the expectations of the user [21]. Some of the well-known models with application in air transport that are used for the purpose of measuring user expectations in relation to perception are VIKOR and SERQUAL. The essence of the mentioned tools is to identify the so-called gap or difference between user expectations and their perception of the actual service. Customer experience management (CEM) manages the needs of travelers in order to achieve and/or exceed the traveler's expectations. Airports constantly review the services provided to users in order to respond to the increasing challenges of meeting user needs [22]. If the elements that increase passenger satisfaction are recognized, including timely reaction, it is possible to increase the airport's income. More and more airports are prioritizing improved passenger service because they have recognized that the higher quality of service provided to users creates a positive effect both on the airport and on its entire community/environment. Each airport aims to understand and accept the factors that influence the increase in user satisfaction [23]. By obtaining information about which factor has the greatest positive impact on passengers and their satisfaction, each airport implements certain measures and procedures in order to improve the services it offers. [PERSON] et al. [24] focused on the factors such as airport cleanliness, staff friendliness, ease of movement through the passenger terminal, ambience, waiting time in the line, and the security control as the key indicators of user satisfaction in most airports. Passengers most often form a perception of the airport after their first interaction with the airport (e.g., in person, via the internet, or self-service). [PERSON] et al. [25] state that the quality of the travel experience is influenced by the accompaniment of passengers and the availability of commercial facilities. Today's liberalization, privatization, and globalization have increased the responsibility of airport operators to provide and maintain an adequate airport service quality (ASQ) [26]. For this reason, airports are increasingly focusing on quality management while measuring customer satisfaction. Each airport has its own methods for conducting passenger satisfaction surveys with the services provided. Conducting surveys on quality of service and evaluating the results obtained provides guidelines for improvement. Given the increasing competition, airports are forced to maintain an adequate LOS and constantly review areas where improvements are possible. By monitoring technological developments and offering a wider range of services, airports can achieve greater competitiveness. User satisfaction is directly affected by their perception of the service received, which ultimately affects the definition of the LOS at a particular airport. In general, this is how the airport's rank in the market is determined. If passengers' expectations are largely met, this implies the re-use of services but also passing on their positive experience to other potential users. Finally, in order to achieve the best possible profit in an increasingly competitive market, airports \"fight\" for each individual user. Following the above, they began to concentrate on user touch points (ASQ enablers) [27], with the aim of improving the quality of service in order to become as competitive as possible in the market. ASQ enablers (Figure 1) can be observed as early as the moment a passenger first considers using air transport services, long before arriving at the airport for departure, meaning that ASQ is concerned with the accessibility of the airport to the passenger, as well as the means of getting to the airport. In order to achieve the desired level of service (LOS) in an airport passenger terminal, researchers in this field use various methods.