CAPACITY OPTIMISATION CONFERENCE FOR AIR
TRAFFIC CONTROL, BRUSSELS, 2001

How does procedures design affect ATC capacity?

Capacity restraints
There are various parameters that define the overall capacity of an ATC system or service:

Sectorisation

Co-ordination procedures within the service

Co-ordination procedures with adjacent ATC services

Airspace/air-route planning and design (for en-route ATC)

Terminal procedures design (for terminal ATC)

Design of ground movement on airports

Ground handling capacity

The controller’s tools (Radar workstation)

The controller’s ability to use his tools

The controller’s knowledge of his airspace

The quality of each individual controller

“Procedures design” can take care of two of the points above: Airspace design and terminal procedures design.

The en-route case
In case of en-route capacity, the solution is actually quite simple: We need routes that concentrate the traffic flow in one direction and has as few crossings as possible. How to get there though is a totally different story. Routes from A to B should be as short and direct as possible in order to be economic for airlines and ecological for the environment. In the 70s or 80s with conventional navigation the air-route planners had to refer to the existing infrastructure, such as VORs and NDBs.

Today, with RNAV we are in a better position. Nevertheless, it takes a huge amount of planning to harmonise the route planning in an area with highly dense traffic and a lot of different ATC systems, services and regulations. But the goal for the designers is clear: segregate the major traffic flows and have as few crossings as possible in order to take some workload off the air traffic controller.

The terminal case
Again, the magic word is called “segregation”. By segregating the inbound traffic flow from the outbound traffic flow, the controller’s task will be less complex and therefore he will have a higher capacity. Studies prove that the capacity of an ATC sector decreases as a reciprocal of the complexity of the traffic handled.

However, segregation of traffic flows can prove very difficult close to an airport, even if we are looking at a single runway environment. It gets even more complicated when the airport has a multiple parallel runway system and it gets out of control when you have a crossing runway setup…

In the study above we see a simple single runway setup with runways oriented 05 and 23. When runway 23 is in use the arrivals from the northwest would interfere with all departures heading in a northerly direction, even though the two flows are totally segregated. If this particular example happens to be close to a state border, the procedure designer would probably have no influence on the routing in the neighbour state. The designer would have to deal with the actual parameters.

An example could be as follows: Inbound traffic is delivered at fix A descending to FL 180, outbound traffic has to be delivered over fixes B and C climbing to FL 240.

The actual separation of inbound and an outbound flight would take place in the terminal area. Depending on the climb and descend profiles of the aircraft, the separation task will be more or less complex.

The pre-planning phase
In order to find out how this particular problem could be resolved, the designer has to have some options. The options have to be pre-planned and co-ordinated with different interested parties: Obviously ATC would play a major role in this pre-planning process. But before starting an intense and time consuming study we must find out if there are environmental constraints. In the pre-planning phase the designer can only guess what solution would increase the capacity – an actual capacity increase will only be proved when the procedures are fast time simulated.

Designing procedures
In this example, it is worth evaluating the following options:

Establish two new fixes D and E to make the flown tracks longer. Due to the longer tracks flown, the inbounds should be below the outbounds at the crossing point. Where exactly these fixes have to be established is a constant trial and error process. Again, a fast-time simulation tool can help show which layout works better.

Establish one new fix (F) at a convenient location, where the inbound flow crosses the outbound flow. The fix has to be at such a position where the outbound traffic is above the inbound traffic at all times. This kind of procedure would even work in case of radar failure. The controller could issue conditional clearance (climb to FL 240, cross F at FL 190 or above/ descend to FL 100, cross F at FL 180 or below).

These are some simple examples of a single runway setup. If you have multiple runways and/or limited amount of airspace, the whole process of finding solutions becomes more complicated.

Operational support versus operational drag
ATC is a quite dynamic environment. Changes take place at a fairly constant pace and if the operational support services, such as procedures design and fast-time simulation cannot keep this pace, or actually be in ahead of a problem, the ATC system suffers from a significant capacity loss. New procedures have to be developed quickly and accurately, as it is a long process until ATC can actually use them:

Tools
In a modern ATC environment it is important that the staff has the most recent technology available. Modern Radar displays with a reliable radar data processing system, MSAW (minimum safe altitude warning system), STCAS (short term conflict alerting system) and customized radar workstations (controller logs in with a code and all his display settings are restored) are (or should be) the normal standard in high-density traffic environments.

The same applies to procedure design. If the procedures are designed with paper and pencil, it will take months to actually find solutions, which eventually result in a capacity increase. Should fast-time simulation prove that they don’t, it will take another month or so to adjust the procedures or to find completely new ones.

Using an automated design tool, this task can be completed faster and safer. This is because a design tool has a function to import and export databases (obstacles, airspace, navaids, routes, waypoints) and therefore the potential for error is significantly reduced, as the designer would use a common database.

When a procedure has to be modified i.e. a fix has to be moved by 2.5 NM to the northeast, the designer is only a couple of mouse clicks away from the result.

An automated design tool will also assist in the planning of upper air routes as well as airspace design. A design tool can even be used to create maps for radar displays.

Example of designing airspace in 3D.

Example of creating simulated terrain with a design tool.

Example of obstacle assessment for an ILS approach

Example creating an approach chart with a design tool

Example of air-route design (segregation of northbound and southbound traffic flows)

The RNAV Role
RNAV will be of great help in the future to establish procedures which will help to increase capacity. However, due to the large number of possible solutions there will be a great need for harmonisation between states. The fact that new routes do not have to follow an infrastructure on the ground (VORs, NDBs), will allow for a much more flexible and efficient use of airspace.

However, in terminal areas, inbound and outbound traffic will always have to be separated and unless the planes fly considerably longer flight paths, there will always be a conflict point where the air traffic controller will actively have to establish separation.

In order to increase the capacity of the ATC sector, the controller should have to intervene as little as possible. Forcing an airplane to fly more track miles in order to gain altitude is a possibility to reduce the controller’s need for intervention, but it is not the most efficient method to increase a sector’s capacity, because the aircraft occupies more airspace for a longer time.

Extreme example of establishing a significantly long outbound route in order to gain altitude before the outbound route crosses the inbound route.

Conclusions
If the procedure design process is well integrated in ATC capacity research and development work, it can help to identify potential conflicts at an early stage and will be able to provide a series of possible solutions to avoid such conflicts. It is important to incorporate all parties in the pre-planning phase (ATC, airport authorities, etc…).

When an automated design tool is used, the procedure designer can provide many solutions in a short time, he can present a trial and error concept without losing too much time, and last but not least, safety is assured due to use of common databases and computer internal calculations.

Finally, the series of possible procedures have to be handed over to a fast-time simulation team who can simulate the new traffic patterns by using actual traffic data from an ATC service.

©June 2001.

Beat Zimmermann is the procedure design instructor for Wavionix Software Ltd, the market leaders in award winning software tools for procedures design.

If you have any queries regarding this paper, please contact:

Beat Zimmerman: beatz@wavionix.com   For further information on Wavionix Software:

wavionix@wavionix.com

www.wavionix.com