Air Traffic Control | Research & Encyclopedia Articles

Air Traffic Control

A horrible air disaster occurred in the skies over the Grand Canyon in 1956, when a two commercial aircraft, operated by Trans World Airlines and United Airlines and flying in clear skies, collided and crashed, killing more than 100 people. As a result of this tragedy, Congress in 1958 established the Federal Aviation Administration (FAA), to regulate and oversee the operation of aircraft in the skies over the United States, which were becoming quite congested. The resulting structure of air traffic control has greatly increased the safety of flight in the United States, and similar air traffic control procedures are in place over much of the rest of the world as well.

Rudimentary air traffic control (ATC) existed well before the Grand Canyon disaster. As early as the 1920s, the earliest air traffic controllers guided aircraft in the vicinity of airports manually, using lights and flags, while beacons and flashing lights were placed along cross-country routes to establish the earliest airways. This purely visual system was useless in bad weather, however, and by the 1930s, radio communication was coming into use for ATC. The first region having something approximating today's ATC was New York City, with other major metropolitan areas soon getting ATC centers as well.

After World War II, ATC centers could and did take advantage of the newly developed radar and improved radio communication brought about by the war, but the system remained rudimentary. It was only after the creation of the FAA that full-scale regulation of America's airspace took place, and this was fortuitous, for the advent of the jet engine suddenly resulted in a large number of very fast planes, reducing pilots' margins of error and practically demanding some set of rules to keep everyone well-separated and operating safely in the air.

Many people think that ATC consists of a row of controllers sitting in front of their radar screens at the nation's airports, telling arriving and departing traffic what to do. This is only a ver incomplete part of the picture. The FAA realized that the airspace over the United States would at any time have many different kinds of planes, flying for many different purposes, in a variety of weather conditions, and the some kind of structure was need to accommodate all of them. The following elements were put into effect.

First, ATC extends over virtually the entire United States. In general, from 1200 feet above the ground and higher, the entire country is blanketed by controlled airspace. In certain areas, mainly near airports, controlled airspace extends down to 700 feet above the ground, and, in the immediate vicinity of an airport, all they way to the surface. Controlled airspace is that airspace in which FAA regulations apply. Elsewhere, in uncontrolled airspace, pilots are bound by far fewer regulations. In this way, the recreational pilot who simply wished to go flying for a while without all the strictures imposed by the FAA had only to stay in uncontrolled airspace, below 1200 feet, while the pilot who did want the protection afforded by ATC could easily get it.

The FAA then recognized two types of operating environments. Good weather conditions would permit flying under visual flight rules (VFR), which, as the name implies, suggests a strong reliance on visual cues to maintain an acceptable level of safety. Poor weather conditions (as well as some other conditions, described below), necessitated a set of instrument flight rules (IFR), under which the pilot relied on attitude and navigational information provided by the plane's instrument panel to fly safely. On a clear day, a pilot in controlled airspace can choose a VFR or IFR flight plan, and the FAA regulations were devised in a way to accommodate both VFR and IFR operations could in the same airspace. A pilot can only choose to fly IFR if he or she has possesses an instrument rating, however, which is above and beyond the basic pilot's license that must also be held.

Controlled airspace is divided into several different types, designated by letters of the alphabet. Uncontrolled airspace is designated Class G, while controlled airspace below 18,000 feet above sea level and not in the vicinity of and airport is Class E. All airspace above 18,000 feet is designated Class A. The reason for the division of Class E and Class A airspace stems from the type of planes operating in them. Generally, Class E airspace is where one finds general aviation aircraft (few of which can climb above 18,000 feet anyway) and commercial turboprop aircraft. Above 18,000 feet is the realm of the heavy jets, since jet engines operate more efficiently at higher altitudes. The difference between Class E and A airspace is that in class A, all operations are IFR, and pilots must be instrument-rated. This is because the aircraft at these altitudes operate at very high speeds, with little margin for error, and ATC control of the entire airspace is essential.

Three other types of airspace, Classes D, C, and B, govern the vicinity of airports. These correspond roughly to small municipal, medium-size metropolitan, and major metropolitan airports, respectively, and encompass an increasingly rigorous set of regulations. For example, all a VFR pilot has to do to enter Class C airspace (such as that around Norfolk, Virginia and comparably-sized cities), is establish two-way radio contact with ATC. No explicit permission from ATC to enter is needed, although the pilot must continue to obey all regulations governing VFR flight. To enter Class B airspace, such as on approach to Chicago O'Hare, an explicit ATC clearance is required. The private pilot who cruises without permission into the airspace over O'Hare risks losing his license.

In addition to the airspace classes, the FAA created a network of airways and navigational aids to assist pilots. Two sets of airways exist, the low-level network, in Class E airspace, and the upper-level IFR airways in Class A airspace. A pilot uses these airways to devise an IFR flight plan, and can confidently fly them even in a solid mass of clouds, since no VFR traffic can operate amidst clouds and since ATC will ensure that no other IFR traffic threatens the safety of the flight.

The men and women who staff air traffic control centers work at airports, handling traffic on the ground, as well as departing and arriving traffic, traffic entering an airport's control area, and traffic en route between airports, at a variety of altitudes. Traffic is "handed off" from one control center to another by ATC direction, requiring only a change of radio frequency from the pilot. We hear frequent comments that the ATC hardware in the United States is antiquated, even dangerously so. While the system could probably benefit from equipment upgrades, we should also recognize that it has developed since 1960 into a network of staggering complexity, and that it works very well. The remarkable safety of commercial air travel results not only from the quality of the aircraft now being produced, but from the protective umbrella, stemming from the needless tragedy over the Grand Canyon, that governs to movement of aircraft in our very crowded skies.