Carolyn C. Smith
The control of air traffic follows many concepts similar to those involved in the control of land traffic. They both have the same basic objective the prevention of collisions between vehicles involved. An efficient Air Traffic Control System would be one in which aircraft flow is restricted only by volume and not by limitations of the system.
There are two principle methods which have been employed to provide protection from the hazard of collisions between aircraft.
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The first method is based on the concept that when aircraft are being flown in weather conditions where pilots can see and be seen, the individual pilot is responsible directly for avoiding collisions with other aircraft. This follows the same connotation that each automobile driver looks out for other traffic.
The other principle method relies on the ground based Air Traffic Control Management Service. This service is designed to provide separation between aircraft operating in accordance with the instrument flight rules, primarily when weather conditions don’t warrant the pilot to see and be seen. The system then provides instructions to the pilot as to altitudes and flight paths to be followed. (See Diagram Below)
(figure available in print form)
One important factor of the Air Traffic Control System is reliability. This means that equipment such as aids to navigation, radar, and communications must be properly maintained to meet the needs of the user. As you can very well see, the Air Traffic Control System depends upon the cooperation of both the pilot and the controller.
The provisions of Air Traffic Control Service throughout the world are applied in various degrees. A lot depends on the needs and the capability of each country to supply those services needed. As sophisticated as the world has become, there are many portions of the world’s airspace and many airports which have no form of Air Traffic Control Service.
Those facilities providing area or en route control service are usually the same everywhere. These centers are provided with a complex communication network which connects them to all the airports and other aviation facilities which are within their area as well as adjacent centers. The workload of the controllers can be heavy at times. In order to maintain a controller’s workload at a level in which he can handle or maintain, the centers are divided into sectors. This airspace is a defined geographical area which is made up of a number of airways or routes, airports, and navigation aids. Each sector is assigned a certain number of controllers and assistants who are responsible for all aircraft in their designated sector. During periods of low traffic density, provisions are made to combine sectors. (See Diagram Below)
(figure available in print form)
Flow control has been developed over a number of years as a method of monitoring the flow of air traffic into busy airports. The main objective of the flow control service is to regulate or restrict the flow of Instrument Flight Rule traffic within an affected area. It also regulates or restricts air flow at a specific altitude. Flow control forecasts are issued from time to time to indicate the anticipated delays expected during given periods of time. Flow control normally is applied when 1) arrival delays will exceed 15 minutes and are expected to prevail for an extended period of time; 2) when route segments require prevention action to avoid traffic jams,; 3) when traffic flow is disrupted due to a breakdown of navigation facilities; or 4) where weather conditions have caused excessive delays in executing normal landing procedures.
The control of air traffic on or in the vicinity of the airport is provided by an airport traffic control tower. For the most part towers are located on top of a high building. The controllers are able to observe aircraft movements anywhere on the airport surface as well as the surrounding airspace. The lookout point of the building is sometimes referred to as the tower cab. It is a completely enclosed glass room. The size of the tower cab depends on the number of controllers who will operate from it. (See Diagram Below)
(figure available in print form)
Those departing aircraft are given instructions regarding when and how they may taxi from loading ramp to the runway. They are also given instructions of takeoff clearance when the pilot is ready and the traffic at the airport permits. Arriving aircrafts are handled by the same control tower in a similar manner by clearing the aircraft to land and by issuing appropriate taxi instructions to guide the aircraft to its unloading point.
Some airports are very busy and they utilize the Automatic Terminal Information Service (ATIS) to give instructions to pilots of departing and arriving aircraft. This service consists of a continuous radio broadcast on a special frequency of recorded and periodically updated noncontrol congestion and controller workload. This broadcast includes information regarding altitude, visibility, wind directions, wind speed, altimeter settings, and runways in use.
