Air Traffic Control
Michael S. Nolan Purdue University
The primary function of an air traffic control (ATC) system is to keep aircraft participating in the system separated from one another. Secondary reasons for the operation of an ATC system are to make more efficient use of airspace, and to provide additional services to pilots such as traffic information, weather avoidance, and navigational assistance.
Not every aircraft may be required to participate in an air traffic control system, however. Each nation's regulations only obligate certain aircraft to participate in the ATC system. ATC participation in each country may range from mandatory participation of all aircraft, to no ATC services offered at all.
The level of ATC services provided is usually based on each nation's priorities, technical abilities, weather conditions, and traffic complexity. To more specifically define and describe the services that can be offered by an ATC system, the International Civil Aviation Organization (ICAO) has defined different aircraft operations and classes of airspace within which aircraft may operate. Different rules and regulations apply to each type of aircraft operation, and these rules vary depending on the type of airspace within which the flight is conducted. Although ICAO publishes very specific guidelines for the classification of airspace, it is the responsibility of each country's aviation regulatory agency to categorize its national airspace.
Visual meteorological conditions (VMC) are defined as weather conditions where pilots are able to see and avoid other aircraft. In general, pilots flying in VMC conditions comply with visual flight rules (VFR). VFR generally require that 3 to 5 miles of flight visibility be maintained at all times, that the aircraft remain clear of clouds, and that pilots have the responsibility to see and avoid other aircraft. Pilots provide their own