Do you know there are some restrictions about liquid at the airport ? so, In order to transport you securely to your journey, the TSA employs a complex approach to security that includes passenger screening at airports. The 3-1-1 rule is imposed on how many fluid ounces can you take on a plane for your better journey . While the Transportation Security Administration will scan the substance of your luggage if you are leaving the US, Southwest will just check the size of your bags.