In the document "Flightpath 2050" the European Commission sets out its vision for the continuing development of aviation, in particular with regard to increasing efficiency and reducing environmental pollution. With this in mind, the aviation industry is increasingly relying on satellite-based navigation services. This trend is further reinforced by the research projects SESAR in Europe and NextGen in the USA and is delivering many new possibilities for the design of air transportation.
Satellite navigation opens up the possibility of new flight routes which save fuel and limit damage to the environment. Alternative routes for landing approaches (e.g. curved approaches) reduce noise pollution in residential areas and increase efficiency in an increasingly densely travelled airspace. Satellite navigation is therefore in the process of transforming air transportation and Flightpath 2050 describes the role that satellite navigation will play in future.
One problem presented by global satellite navigation systems (GNSS) in comparison to ground-based systems is that the signal strength received at the user antenna is very low. Thus, foreseeable as well as unforeseeable problems may lead to local or even regional failure of the system. Increased activity in the ionosphere can also prevent GNSS-based services from functioning. Fluctuations in the ionosphere are able to distort the navigation signal so much that it becomes unusable for aviation purposes.
Bearing in mind that, as outlined above, the organisation of aviation depends on GNSS, alternative processes are important in order to guarantee the safety of participants in the case of system failure. To achieve this, a secondary system is required which at the minimum guarantees the safe return to ground of all affected aircraft. Ideally, however, a system of this kind would also enable air traffic to be maintained without interruption in order to prevent financial losses. In order to achieve this, the secondary navigation system must meet comparable criteria to GNSS with regard to precision, flexibility and integrity.
The "Alternative Positioning System" (ALPS) project involves the design and development of an "Alternative Positioning Navigation and Timing" (APNT) system. The ALPS project team will design a holistic system concept for APNT intended to unite a range of technologies for measuring distance, such as L-DACS (L-Band Digital Aeronautical Communication System), DME (Distance Measuring Equipment) and ADS-B (Automatic Dependent Surveillance - Broadcast), with other sensors. The system is intended to enable air traffic to continue with as little disruption as possible in the case of a failure in the satellite navigation system, even if future procedures place higher demands on the navigation system than is currently the case.
As part of the ALPS project, the algorithms and processes required for the holistic system are being developed and even validated in simulations as well as in test flights. The concepts are being presented to groups of experts and international standardisation committees. This brings the results of the project into the decision-making process for a new APNT system.
The Institute of Communications and Navigation is leading the ALPS project. The Institute of Flight Guidance has taken on the task of developing an evaluation platform for validating the algorithms and concepts generated as part of the ALPS project. Subsequently the Institute will carry out traffic simulations for example air spaces in order to validate the overall concept.
DLR-Institut für Kommunikation und Navigation (Lead)
DLR-Institut für Flugführung