Air Traffic Control

Air Traffic Control is the set of tasks involved in directing planes from ground so that the planes navigate along pre-defined safe routes free of obstacles while at the same time maintaining adequate separation in between them so as to avoid collision.

Air Traffic Controllers perform this task by gauging the planes’ position from ground using a variety of techniques and issuing directives to the pilot. They speak to the pilot using radio communication and in order to avoid ambiguity in the information being exchanged they use a refined form of the language called “phraseology”.

Air Traffic Control is performed in stages depending on how far the plane is. Aerodrome control involves the separation of planes which are about to land, just taken off, on the runway, on the taxi way or in some moving phase on ground. It is carried out from the control tower of an airport and is the only type of Air Traffic Control where the Controller can actually see the plane.

Aerodrome Control is performed from a tower that gives the view of the entire airport. Planes on the apron, taxiways, runways as well as those in air in the vicinity are controlled. (Picture source:www.redstate.com)

Terminal control or Approach Control is the task of maintaining separation between planes just beyond the visual range of an airport extending to a distance ranging from 30 to 50 Nautical Miles (learn more ). During this phase planes would have either just departed or are on the way to land and are therefore at relatively low altitudes and with low separation between each other. There could also be planes which are ‘over flying’ in that they are merely passing that part of air space neither approaching nor having departed from that particular airport. The Controller cannot see the plane but has radio contact with the pilot.

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Controller at an Approach Control Centre (Picture source:www.flickr.com)

Terminal Control can be done in two ways. One way is by using various technologies which enables the Controller to locate the plane in air without actually seeing it. These technologies extend beyond the human range of vision and are able to create an artificial image of the air space being controlled in which the Controller can see the plane as a ‘target’. Special equipment and advanced software are used to create this image. The Controller uses the image to keep track of the position of the planes relative to each other and directs the pilot using radio communication to maintain the required separation. This is called ‘Surveillance Control’.

One such technology that is widely used for Surveillance Control is RADAR ( learn more). There are other more modern technologies also that are in use today. The fundamental enabler behind 'Surveillance Control’ is the ability for the Controller to ‘see’ the plane virtually which is the next best thing to being able to see it visually. The RADAR equipment must be deployed at suitable locations within the air space so that it provides the necessary illumination to detect the planes and locate them on the artificial image. Deploying and maintaining these equipment in serviceable condition is also a responsibility of the ANSP similar to that of the Nav Aids.

A Surveillance Controller concentrating on the screen showing the distribution of planes within the control sector. This image is created by processing the data captured from RADAR antennae, using advanced software. The controller can maintain safe separation between planes using the image (Picture source: www.economist.com)

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The other way Terminal Control could be performed is for the Controller to use a mental image of the air space in his mind instead of a virtual image that he can see. When the planes are far away from the airport and high up in the sky, their positions cannot be precisely defined from ground. The controller locates each plane that is in the airspace by estimating its position using the speed of the plane and information obtained from the pilot. He then creates a mental picture in his mind and directs the pilots from ground to maintain the separation required to avoid collision. Since the estimated position could be somewhat different to the actual position that could be seen on the artificial image used in Surveillance Control, the Controller copes with this uncertainty by maintaining a larger separation between planes using a well-defined set of rules or procedures. This way of controlling which has no visual component and is totally dependent on voice communication with the pilot and positions calculated by the controller, is called ‘Procedural Control’. A skilled Controller can use ‘Procedural Control’ as effectively as ‘Surveillance Control’ to maintain separation between planes and Air Traffic Controllers globally take pride in their ability to control air traffic using either of the two methods. But due to the smaller separation  permitted by surveillance control which in turn enables the packing of more planes into the same air space at a given time, surveillance control is considered more efficient and is preferred while procedural control is used in exceptional situations.

Flight progress strips are used to keep track of the planes in procedural control. (Picture source: www.island-images.co.uk)

Terminal air spaces are not adjacent to each other and a plane seldom passes from one terminal control to another. The space between the terminal air spaces are controlled using ‘Area or Airways Control’ (sometimes also called ‘Centre Control'). Planes in this space are generally at high altitudes and flying on a predetermined route towards the terminal airspace of its destination airport. The number of planes are also large because these air spaces are essentially ‘trunk’ air spaces to which planes enter from or exit into several bordering terminal air spaces. The greater part of an FIR will consist of such airspaces and the Area Controller maintains separation between planes flying within this space. Like in Approach Control, Area Control also can be carried out as ‘Surveillance Control’ or as ‘Procedural Control’ but the larger number of planes which makes congestion a critical issue, makes ‘Surveillance Control’ the preferred method.

Controllers at an Area Control Centre. (Picture source: www.ivao.ch

Air Traffic Control is a very stressful profession that requires extensive training. Air Traffic Controllers also need to maintain a high degree of medical fitness to cope with the job related stress. After receiving training, the Controller is issued with a license from the regulating authority for the particular air space without which he cannot practice in that air space. The license must be periodically renewed and the medical fitness is ascertained at each renewal.

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