Control of approach

The control of approach is a Organisme of the air traffic charged to ensure the Services of the air traffic for the benefit of the aircraft in the airspace controlled in the vicinity of a Aérodrome.

General information on the control of approach

The purpose of the control of approach is to ensure the services of the air traffic in spaces close to the aerodromes. In these spaces can evolve/move of the aircraft at the beginning, which wish to go up, of the aircraft on arrival, which wish to go down, and of the aircraft in transit, which wish to maintain their altitude. Control must also ensure the compatibility of the traffic flying the instruments (airliners and of businesses in general) and wheel at sight (private planes in general). It must also manage helicopters, parachuting, stunt-flying, drives, sailplanes…

Physical localization

In France, the control of approach is physically localized in control towers. In this case, it is localized in the watchtower of the tower or a room of separated approach when it exists. The room of approach is sometimes immediately under the watchtower (Basle-Mulhouse, Orly) or at the ground floor (Roissy, Bordeaux, Toulouse, Clermont Ferrand etc). However, the controllers of centers on the way are brought to make control of approach on certain isolated grounds which do not have local control of approach for which no close approach is responsible. The control centers of approach ensure control for several grounds known as “satellite”. For example, the approach of Nice manages that of Cannes. In the world, certain countries chose a regrouping of the approaches in TRACON (Final Radar Approach CONtrol) as in New York or Washington. Others integrated the near total of their controls of approach in great centers as in England or Germany. Intermediate situations exist, and, as example, it is envisaged under ten years to gather the approaches of Orly and Roissy in a common center in Paris region.

Methods

The characteristic of the control of approach is to manage a great diversity of apparatuses, very evolutionary and having great differences in speeds. That goes from the mongolfière or the sailplane to the quasi-supersonic fighter plan while passing by the helicopters, the ULM and the airliners. Although almost all the aerodromes have such traffics, one speaks about approach only when the airspace considered is a controlled space. This excludes the small aerodromes.

The controller has two means to ensure this monitoring service:

the Information of traffic, which is ensured like everywhere: the controller collects information on the position of the aircraft with which it owes the information of traffic, and retransmet this information as for the aircraft for which information is relevant.

the Spacing, and in this case the work methods vary according to average the techniques the controller has, in particular of the means radar. The controller can not be equipped with radar, to have of a radar which is not approved for guidance, or a radar approved for the three services radar.

Traditional approach

One calls traditional approach an approach which does not answer the criteria of the approach of précison, this one at least comprises 3 simultaneous information of guidance in azimuth, height, and distance, THEY, Glide, DME for example. The control of approach can be carried out with or without radar of guidance, with 2 electric radio assistances, the operational minima being raised. The character pitches are then ensured by strategic separations.

For two aircraft on arrival, one generally ensures a vertical separation: if two aircraft arrive at the same time, they are left one with the top of the other, the second going down when the first goes down. Once the first posed, second is authorized with the approach. The order answers the rule of the " arrived first, first servi".

For two aircraft at the beginning, the method employed is equivalent. The aircraft left in first goes up, that party in second remainder in lower part, and is authorized to assemble progression of the first progressively. Once a horizontal separation obtained (if their trajectories diverge after the take-off), the second is not restricted any more for its rise.

When an aircraft leaves on a trajectory, and that another arrives on a virtually identical trajectory, in general a criterion is defined to know when these aircraft are separate. The aircraft on arrival must pass a characteristic point, and the aircraft at the beginning another point. From this moment there, a spacing is established, and separation will do nothing but increase. One can then make descend the arrival, and make assemble the departure.

Of course, the situations of real control consist of much more than two aircraft, but generally the cases can be broken up into a series of these academic cases.

Radar approaches

Assistance, monitoring

Assistance radar : Use of the radar to provide information to the aircraft on their position or of the variations compared to their road.

Monitoring radar : Use of the radar for better knowing the position of the aircraft. It is about an approach where no guidance radar is carried out, but where the radar is used to accelerate the crossings.

The methods are the same ones as for the traditional approach. However, instead of awaiting the criteria of strategic separation to carry out crossings (especially in the case of an aircraft on arrival and of one at the beginning), one uses a spacing radar which is in general reached much more quickly than a strategic separation. Moreover, the radar makes it possible the aircraft to follow trajectories not standards, for which no strategic spacing is defined. It gives to the controller a tool to note a character pitch between aircraft who follow such trajectories.

Lastly, the radar increases safety, while making it possible to the controller to monitor that its instructions were well included/understood and followed by the pilot.

Guidance radar

When guidance radar can be used to ensure the control of approach, the control methods change considerably. The controller can assign courses with the aircraft on arrival in addition to altitudes and speeds. The goal is them “to put the ones behind the others” and to accelerate and order flows so as to obtain the best sequencing. The distance between the guided planes is determined by the capacity of the track. This one depends on the instruments of navigation used by the pilots during the final approach, but also on the meteorology and the morphology of the airport. For example, if there is only one track, one will need more distance between the planes on arrival to make it possible to take off other planes at the beginning. If the visibility is very degraded, the capacity of the track decreases considerably.

The controller of approach guides the planes towards the point of final approach from where they become again autonomous, it ensures the rate envisaged according to the procedures in progress and of local meteorology on the ground. Thanks to guidance, it is also possible to establish a horizontal separation between two aircraft at the beginning or an aircraft at the beginning and another on arrival. The contolor must however respect well defined standards of spacing radar. According to the material available, they are of 3,5 or 8 Nm (1 Nm = 1852 m) horizontally and of 1000 ft (1000 feet, approximately 300 m) vertically in Metropolitan France. The standard is of 3 Nm in the sectors of approach in Paris region, lowered to 2,5 Nm once the apparatus established on THEY. These distances are those observed at least between the two planes concerned.

When a controller guides a plane, it entirely takes charges with it its navigation (course, altitude, speed). It is responsible for the safety of the plane with respect to the other apparatuses in guidance. Moreover, to any moment the controller does not give a clearance worms of altitudes lower than minimal altitudes of safety. These data are published and are available on the posting of the radar screen of the controller. The crews have a comparable chart. However, as it can be difficult to them to know exactly their position during a guidance, the responsibility for anti-collision (with the ground) is entirely entrusted to the controller. Out of guidance radar, the commander is responsible for his safety with respect to the relief and remains Co-person in charge of anti-collision with the other aircraft.

On the very large airports, guidance radar is the nominal method to bring the planes of their point entrance to their point of final approach. On the smaller airports, there is co-education of methods between guidance radar and monitoring radar of the planes remaining on trajectories published.

See too

Internal bonds

Control of the air traffic
TRACON on the anglophone site of wikipedia

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