The outbreak of the COVID-19 pandemic in 2020 seriously impacted the world. Some previous researches suggest that global incidents could strongly influence the demand for passenger air transport services (Sobieralski, 2020). And the impacts on the demand can be ascribed to the change in the air travel behaviour of travellers (Ito & Lee, 2005). However, the influence of a pandemic on passengers’ air travel behaviour has been rarely studied. This thesis studies the differences in air travel behaviour between the COVID-19 period and the non-pandemic period, in order to benefit the decision-making of policy-makers.In this thesis, it is assumed that the COVID-19 pandemic influences air travel behaviour through changing the air transport context. Three context aspects are found to influence how air travellers behave during the pandemic. Firstly, the policies including travel restrictions and travel recommendations imposed by the government discourage travel motivation. Secondly, the rise in public risk perception triggers their health-protective behaviour which leads to low willingness to fly or changes in travel choice decision-making. The operation adjustments of the airlines in response to the COVID-19 pandemic also influence the offered flight options in the market which could change flight choice behaviour.Two important air travel choice behaviours during the COVID-19 pandemic are further studied, which are the choice between flying and not flying (willingness to fly) and the choice between flight alternatives. Stated choice data is used since it avoids the bias of revealed choice data in studying willingness to fly. Discrete choice modelling is used because of its advantage in studying individual choice.Air travel convenience and airborne health safety are considered important to air travel choice-making during the pandemic. Therefore, they are added as two attributes in the stated choice experiment. The perception of them is scaled by the perception rating experiment using the Hierarchical Information Integration theory. The results show that the perception of air travel convenience is influenced by the requirement of health-related paperwork, such as health statement and virus test result, for travelling and the travel flexibility, such as change and return policy given, by the airlines. The perceived health safety is influenced by the intensity of the virus precautionary measures implemented in the cabin.The results of the stated choice experiment show a considerable change in the attribute trade-off between flight alternatives made by air travellers during the pandemic. Perceived health safety is the foremost factor that air travellers consider. If an intermediate serious pandemic is assumed, air travellers are willing to pay at least 100% more money to improve the virus precautionary measures by 1 level compared to the non-pandemic situation. This percentage difference becomes larger when the safety level Increases to a higher level, which means that air travellers are more willing to take the safest flight during the pandemic. Transfer and flying time are considered as other two important attribute during the pandemic because they indicate the chance of the exposure to the risky environment. Therefore, travellers are willing to pay 87.9 euro during a serious pandemic to reduce 1 transfer, while they would only pay 42.6 euro during the non-pandemic period. Correspondingly, the ticket price of the flight becomes less important in the exchange for a better performance of other attributes.The willingness to fly is significantly deteriorated by the COVID-19 pandemic. In the case of a serious pandemic, the willingness to fly reduces from 83.5% to 37.6% if the flights in the market have a medium attribute performance. Although improving several flight attributes including price, transfer, travel convenience and health safety can pull up the willingness to fly, however, the negative impact of the pandemic is so strong that even the most extreme attribute improvement, ignoring the profitability and sustainability, still cannot totally offset the willingness to fly reduction because of the COVID-19.The following recommendations are given to policy-makers. Firstly, meeting the customers’ expectation of health safety is the best way for airlines to compete during the COVID-19 pandemic. Two methods to do so include providing non-stop flights as much as possible and improving the intensity of virus precautionary measures in the cabin. Reducing the price is still effective in attracting customers, but less than during the non-pandemic period. Secondly, airlines can increase their load factor by improving flight attributes. But the negative impact of the virus cannot be fully compensated. Thirdly, because the willingness to fly is strongly related to the seriousness of the pandemic, the government should never underestimate the rebound of travel motivation in order to avoid the uncontrollability of the pandemic when the situation gets better. Fourthly, as the COVID-19 is unlikely to disappear soon, the low willingness to fly will remain and threaten the survival of airlines. The governments should work out a sustainable financial aid plan with airlines that can also balance the other goals for the society including economic growth and environmental protection.