Chapter 11:  Airport Operations  Introduction  Types of Airports Towered Airport Non-towered Airport Sources for Airport Data The definition for airports refers to any area of land or water used or intended for landing or takeoff of  aircraft. This includes, within the five categories of airports listed below, special types of facilities  including seaplane bases, heliports, and facilities to accommodate tilt rotor aircraft. An airport includes  an area used or intended for airport buildings, facilities, as well as rights of way together with the  buildings and facilities.  There are two types of airports—towered and non-towered. These types can be further subdivided to: A towered airport has an operating control tower. Air traffic control (ATC) is responsible for  providing the safe, orderly, and expeditious flow of air traffic at airports where the type of  operations and/or volume of traffic requires such a service.  A non-towered airport does not have an operating control tower. Two-way radio communications  are not required, although it is a good operating practice for pilots to monitor other aircraft on the  specified frequency for the benefit of other traffic in the area. The key to monitoring traffic at an  airport without an operating control tower is selection of the correct common frequency. The  acronym CTAF, which stands for Common Traffic Advisory Frequency, is synonymous with this  program. A CTAF is a frequency designated for the purpose of carrying out airport advisory practices  while operating to or from an airport without an operating control tower. The CTAF may be a  Universal Integrated Community (UNICOM), MULTICOM, FSS, or tower frequency and is identified in  appropriate aeronautical publications. UNICOM is a nongovernment air/ground radio  communication station that may provide airport information at public use airports where there is no  tower or FSS. Non-towered airport traffic patterns are always entered at pattern altitude. How you enter the  pattern depends upon the direction of arrival. The preferred method for entering from the  downwind side of the pattern is to approach the pattern on a course 45 degrees to the downwind  leg and join the pattern at midfield.  When a remote pilot operates in the vicinity of an airport, it is important to review the current data for  that airport. This data provides the pilot with information, such as communication frequencies,  services available, closed runways, or airport construction. Three common sources of information are: Remote Pilot – Small Unmanned Aircraft Systems Study Guide  65 • Aeronautical Charts • Civil Airports—airports that are open to the general public. • Military/Federal Government airports—airports operated by the military, National  Aeronautics and Space Administration (NASA), or other agencies of the Federal Government. • Private Airports—airports designated for private or restricted use only, not open to the  general public.