Simulation helps plan for safer and more efficient air traffic control

The Spanish air traffic control provider - AENA - has used WITNESS modelling and simulation tools to investigate how the predicted increase in flights numbers through the country´s airspace will impact on the efficiency of the services they provide.

Real data from a number of sources was used with WITNESS simulation software to create a computerised model through as Mentor tool to test a range of scenarios and provide a better understanding of the inter-relationship between flights, schedules, airports and air traffic control sectors. The results have been used to help plan future developments to increase air traffic capacity and reduce the number of delayed flights.

Success leads to crowded airspace

The state owned AENA (Aeropuertos Espanoles y Navegacion Aerea) bears responsibility for the maintenance and operation of Spain´s air traffic control system and the country´s 43 largest airports. Safety is paramount but efficiency, value for money and high quality of service, is also very important.

Business and leisure growth has made Spain one of the most popular destinations in Europe. The country's airports currently handle more than 150 million passengers, two million aircraft movements and 700,000 tons of cargo a year. These volumes are predicted to increase significantly in the future and AENA needs to ensure that it can support more flights with the same high safety and quality standards it imposes at present. The organisation asked one of the world's leading transport consulting and engineering companies, to partner it on an airspace structure analyser known as Mentor.

The two organisations have previously used simulation packages to help plan air traffic control operations and decided that WITNESS offered the best solution for their needs

Strect rules for air traffic control

Air traffic control is a complex operation that is designed to guarantee safety and provide aircraft with the best possible route between airports. At any given time there will be many aircraft in the sky and it is impossible for one controller to manage them all. Airspace is therefore split into smaller zones or sectors that can be managed by a single person. Controllers must not be busy for more than 60/70 per cent of the time so that they have time to deal with unexpected events. If too many planes are present in a sector the controller will be busier than the safety margins permit.

There are strict rules about how many aircraft can occupy a sector, when they can enter or leave and where they can fly. Aircraft must be separated by ten nautical miles longitudinally and laterally, and 1000ft vertically when flying below 30,000ft. The speed of aircraft means that these seemingly large distances may equate to just a few seconds flying time.

One of the principal activities of air traffic control management is to ensure that aircraft can proceed on their journey without flying overloading sectors. If an overloaded should occur a controller´s only option is to hold a flight in progress to its current position or pass it to a less congested sector until it is clear to proceed safely. Flights entering Spanish airspace must also be accommodated within the air traffic control system.

Airborne aircraft must be given priority over those on the ground but this often leads to delays as flights sit on the runway and wait for congestion to clear. More than three quarters of all flight delays are caused this way. Even seemingly simple delays can have a knock on effect to later schedules. Any delays are unacceptable to operators and passengers and the situation is likely to worsen in the future unless AENA can identify new ways of increasing capacity in the system.

WITNESS the MENTOR

Mentor was devised to identify sectors with lack of capacity in the current structure and investigate ways of revising air traffic control operations. In simulation terms, the air traffic control management rules and the parameters that define sectors can be combined to produce a useful but complex interactive model where each sector can be treated as a collection of discrete boxes containing any aircraft. This was created using information from a number of real-life sources including sector layout and capacity, and scheduled and forecast flights.

Mentor (created with WITNESS at the core of the application) has a special user interface to make the system easier for inexperienced staff and to allow user-defined parameters and inputs from external data sources. This makes it easy for experienced and inexperienced AENA staff to test a number of scenarios. The resulting models are designed to be dynamic so that parameters can be changed during the simulation to provide an immediate response. The system includes outputs to spreadsheet and graphical applications supporting a number of interpretive options.

Safe way to see what if

Mentor effectively flies aircraft between the sectors and destinations inside its virtual representation of Spanish airspace. This means that AENA can test a wide range of "what if" scenarios in a completely safe environment without involving any real aircraft or passengers. For any scenario Mentor reveals how demand will vary for each sector over time and highlights any potential bottlenecks that might occur. It also indicates which sectors will overload, how this will create delays and which flights and airports will be affected the most. AENA can use this information to test new configurations and try out different operating parameters to increase individual sector and overall capacity to help reduce the frequency and length of flight delays.

One aspect of air traffic control management that Mentor revealed was a network effect that had been masking other problems in real-life situations. This occurs when an increase of capacity is applied to a specific sector and the problem is solved apparently. However, because of the strict rules and parameters that apply, this theoretically improvement can have a knock-on effect that creates a ripple of over capacity and flight delays elsewhere in the system.

"The insight that WITNESS has given us has been very invaluable," says Francisco Montoto. "It has shown numerous ways of improving our flight handling capacity."