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Control Tower

The primary function of the control tower is to control the runway and the airspace immediately around the airport. The tower also controls the movement of aircraft on the ground. It is the source of the Automated Terminal Information System (ATIS). ATIS is a voice recording of a tower controller. The recording tells pilots about the wind, clouds, visibility and any restrictions that the runways may have. It is updated at least every hour. During changing weather conditions, it is changed much more frequently.

Approximately 95% of the airports in the United States do not have control towers. These airports are called uncontrolled airports. At these airports, pilots must use common procedures to reduce the chances of collisions on the ground and in the air. At some uncontrolled airports, a nongovernment radio facility known as a unicom provides communications between the air and ground. An airport's unicom frequency is designated with a "U" on the airport's sectional chart information. Unicom operators can provide pilots with basic information regarding airport conditions such as current wind speed and direction, preferred runway, and altimiter setting. They can also advise of any reported traffic in the pattern. However, they do not have any control over traffic. It is up to pilots taking off or landing at such an airport to announce their position over the unicom frequency to all other pilots in the area. It is each pilot's resonsibility to see and be seen when conducting operations at these airports.

Other uncontrolled airports have no radio facilities. These are known as multicom airports. Pilots taking off or landing at such an airport will communicate with each other on the multicom frequency 122.9. Again, it is up to pilots using these airports to make their position known to other pilots -- to see and to be seen.