To rebook yourself under the flat-tire rule, it is recommended to reach the airport within two hours after the original departure time. However, please note that this policy is subject to the discretion of the airline employees.If you miss your Southwest flight, the airline has policies in place to handle such situations. Southwest missed flight Airlines will try to accommodate customers who arrive within two hours after their scheduled departure. They will be placed on the next available flight to their destination on a standby basis. This policy is known as the "flat-tire rule," southwest missed flight allows passengers to be rebooked on the next flight without any additional charge.