## 4 Results and Discussion  
### Descriptive Analysis  
To identify any temporal patterns or shifts in factors influencing recommendations, time series analysis was applied to examine trends and fluctuations over time in the passengers' satisfaction, recommendations, and airport feature ratings. This could involve seasonal trends, changes due to airport improvements, or responses to specific events. Understanding these trends can help airport management identify areas needing improvement and track the impact of changes or interventions over time. It is evident that passengers' ratings for various airport-related services or aspects (incl. terminal cleanliness, seating, signage, food and beverages, shopping, WiFi connectivity, and airport staff) vary throughout the year. As examples, Figures 2-4 illustrate these variations for Heathrow, Birmingham, and Manchester airports by aspect, with similar patterns observed at other airports. This indicates that the quality of these aspects changes over time, likely influenced by seasonal effects and the number of passengers served. However, further investigation is necessary for hidden factors impacting the variation. The line charts in Figure 5 below illustrate the annual average rating trends for each service across airports. The terminal cleanliness has shown slight drops in recent years. A notable decline was observed in early 2012. Terminal seating has shown significant fluctuation since 2015, indicating a possible issue of passengers' comfort in seating areas, with more variability but a general negative trend. Terminal signage has a similar variation to terminal seating but with a higher rating. For food and beverage options, passenger ratings showed a decline from the year 2016. Airport shopping ratings generally dropped over the years with fluctuations. WiFi connectivity ratings show slight drops, which are especially noticeable after 2020, likely due to an increase in the number of passengers. Airport staff ratings dropped suddenly in 2020 but improved until 2022, after which the decline continued. Overall, passengers have shown negative ratings toward all airport services in recent years. Figure 2: The changes in passenger ratings for cleanliness of terminals at three UK airports. From these trends, it can be generally observed that most aspects of airports have dropped post-2022. Before this period, ratings were more variable, potentially reflecting inconsistent service levels or differing passenger expectations. These visual trends help airport management identify successful changes and periods requiring further investigation into potential declines in service quality. Overall, passenger ratings from 2022 to 2024 are low across most aspects, indicating that recent efforts to maintain or improve airport services have not convinced passengers. These results suggest that passengers have generally negative perceptions of the services provided by airports during this period. Figure 6 shown below compares the trends of various airport features over time. Terminal cleanliness and airport shopping features show significant variations, suggesting periods of high and low passenger satisfaction. Meanwhile, WiFi connectivity and terminal signs features have relatively stable trends but exhibit occasional spikes or dips, indicating changes in passengers' experience. The trends for terminal seating, food and beverages, and airport staff also show variability, reflecting changes in passengers' perceptions over time. Figure 4: The changes in passenger ratings for airport staff at three UK airports. Figure 3: The changes in passenger ratings for terminal seatings at three UK airports. Figure 5: The annual average rating trend by service. The bar charts in Figure 7 below show the average ratings for each category of airport services across different seasons. Terminal cleanliness ratings are relatively consistent across seasons with slight variations, suggesting that cleanliness standards are maintained throughout the year.