 Mandatory frequency airport

An airport with a mandatory frequency (MF), mandatory traffic advisory frequency (MTAF) or air/ground radio (A/G) is an airport which does not have a control tower but still requires arriving and departing aircraft to communicate with other aircraft or a radio operator on a published frequency.Mandatory frequency airports are rare in the United States, one example being Ketchikan International Airport (), but they are common in other countries such as Canada, Australia, the United Kingdom and Norway; often, an MF or MTAF airport is one with scheduled passenger service but insufficient traffic to support a control tower.