Traffic merging in the air
One development which could help to reduce noise pollution further for those living near Schiphol Airport is conducting Continuous Descent Operations (CDO) along fixed approach routes. With a view to introducing these fixed approach routes to the busy day-to-day operations at Schiphol, Air Traffic Control the Netherlands (LVNL) asked the Knowledge & Development Centre (KDC) to set up a study. This study involved inventorying solutions for supporting air traffic controllers in efficiently merging two or more traffic flows on fixed approach routes into a single flow. The KDC commissioned the National Aerospace Laboratory (NLR) to conduct the preliminary study. This article contains the main findings of the inventory conducted by the NLR.
Air traffic approaches Schiphol from two sides. The idea is to conduct these two flows to the runway via a fixed approach route. Air traffic controllers require a merging tool for this. The merging of traffic which flies along fixed approach routes already occurs at night, when it is quiet. The idea is to use the fixed approach routes during the day as well, when it is busy. Air traffic controllers are not expected to be able to merge this traffic, which flies along a fixed approach route, without system support. The system support is aimed at helping air traffic controllers to merge the safely-spaced aircraft at the merging point. To do so, it is necessary to ensure that the process is working smoothly long before the merging point. The aim here is to keep the traffic on the fixed approach route and to merge it using minor adjustments to the airspeed. The best-possible descent profile, without the intervention of air traffic control, is important to airlines with a view to saving fuel. This also reduces CO2 emissions and noise pollution around Schiphol. The required system support focuses on busy daytime operations, but is also needed to optimise night operations.
The role of the NLR
The KDC was highly satisfied with the NLR’s efficiency in conducting the study. Over the past few years the NLR has gained a great deal of knowledge about traffic merging from participating in European innovation studies. At the start of the preliminary study, the NLR had already incorporated several types of system support into its simulation environment, which greatly benefited the inventory. This enabled the project team to provide corresponding recommendations in a short space of time.
In the preliminary study, together with experts from the LVNL the NLR first identified the requirements and preconditions for operations. In a second step, a market survey was used to identify potential solutions for supporting air traffic controllers in merging traffic flows. An initial evaluation was then conducted by LVNL operational experts (active air traffic controllers). The solutions were tested against various operational aspects, such as acceptance and applicability in operations, but also potential costs, throughput time and resources in the implementation procedure.
The evaluation led to identification of the best solution directions given the operational requirements and all other known preconditions. As none of the identified solution directions was immediately applicable to the situation at Schiphol, recommendations were made based on operations with respect to possible system implementation and the corresponding visualisation options.
The NLR’s CORADA (Converging Runway and Approach Display Aid) was recommended. A CORADA solution was chosen based on spacing using a ghosting concept. This concept is similar to the MITRE Relative Position Indicator (RPI). This recommendation was made given the preconditions for realising the project within a short period (two to four years). The expected informative nature (without displaying solutions) of the support for air traffic controllers also played a part. The ultimate decision on implementation of the ghosting concept will be taken by LVNL. This decision needs to be as simple as possible (without integrated wind information) and including the option of keeping radar screens free from too much information, e.g. by probing, switching ghosts on and off.
The result and recommendations of the preliminary study will be worked out further in the next phase of the study and will lead to a definitive choice of concept. In addition to choosing the concept, this phase will include writing an operational concept document and laying down criteria for demonstrations and validation exercises. Possible implementation options for merging along fixed approach routes have already been examined in a related KDC project, in which real-time simulations were conducted for Interval Management (ASAS-IM) at the Schiphol TMA on the NLR’s NARSIM platform. These options could serve as a basis for working out the concept in more detail.