The flight number is on the ticket. In order to facilitate the organization of transportation and production, each flight has a different number according to certain rules, which is easy to distinguish and manage. This number is called flight number. The flight number consists of the two-character code of each airline plus four Arabic numerals, and the airline code is promulgated by the Civil Aviation Administration. The last four digits represent the area where the airline base is located, the second digit represents the area where the terminal building is located outside the flight base, the third and fourth digits represent the serial number of this flight, the odd number represents the outbound flight from the base, and the even number represents the return flight to the base.