This study aimed to determine the possibility of COVID-19 transmission through in-flight contact during flights for many patients with confirmed COVID-19 during the COVID-19 pandemic and explore infection prevention and control (IPC) methods for overseas infectious diseases. A retrospective cohort study was conducted on flight with a large number of confirmed case among. Delhi- Incheon flights in 2020. This flight was selected to confirm transmission through close contact with the cabin, with a total of 14 confirmed cases out of 190 passengers (including 10 flight attendants). After confirming COVID-19 test results for those entering Korea, we conducted an epidemiological investigation on confirmed patients to determine their general characteristics and epidemiological relevance. We analyzed the epidemiological relevance, occupational information, incubation period, and COVID-19 variation and genotype among confirmed patients who were in close contact with confirmed cases, and analyzed the possibility of transmission according to the distance of close contact in the flight. One confirmed patient was found to be highly likely to be infected due to close contact with the cabin. However, it occurred within two rows, not within 1 meter. In addition, considering the aerodynamics in the cabin and local incidence rate, infection in an unspecified number of local people could not be excluded. It was analyzed that the reason for reducing infection from close contact on board for a long time in a flight with a large number of confirmed cases was the effective IPC method. In order to prevent overseas infectious diseases caused by flights, autonomous IPC management of airlines and passengers is necessary in addition to national quarantine management such as symptom screening before boarding, wearing passenger masks while boarding, food and beverage restrictions, disinfection of public spaces, distancing between passengers, close contact management after boarding, and self-quarantine.