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The European satellite augmentation system, EGNOS, is used to improve the performance of global navigation satellite systems (GNSS), such as GPS and Galileo, for precision applications ranging from land and sea transport to agriculture and fishing, policing and sports – not forgetting the safety-critical applications of civil aviation. The possibilities offered by the system are immense and its applications vast, which is why careful thought needs to be given to planning its possible future evolutions. When it comes to aviation, which future use of EGNOS services would allow significant gains in terms of performance, capacity and safety?

A recent study Egis undertook on behalf of the European Commission looked at answering this question. It took an initial look at the potential operational applications that future versions of EGNOS could support.

Air Navigation Service Providers, EUROCONTROL, airlines, aircraft/system manufacturers and the drone industry were all consulted to gather their current and future needs. This consultation process enabled us to identify a set of applications that would benefit from EGNOS services.


One identified need was linked to the use of surveillance based on ADS-B (Automatic Dependent Surveillance-Broadcast) to complement or replace existing multilateration surveillance used for A-SMGCS (Advanced Surface Movement Guidance & Control System). ADS-B based on EGNOS could be used at airports equipped with A-SMGCS to provide even more accurate aircraft position data, thereby enhancing the performance of A-SMGCS, optimizing the alerts generated for the air traffic controller, and thus further reducing the risk of incident or collisions of aircraft and ground vehicles on runways and taxiways.

Approach procedures

Another opportunity identified by the team was using improved EGNOS performance for approach procedures beyond CATI. These would be equivalent to ILS SA(1) CATI and CATII procedures (with associated decision heights at 150 ft and 100 ft) based on GNSS and without the need for new infrastructure on the ground. This would improve accessibility and allow landing even in degraded weather conditions and with lowered costs due to reduced infrastructure requirements.

New altitude reference system

EGNOS could also support a new altitude reference system based on geodetic altitude instead of barometric pressure measurements. It could cover all classes of airspace, all phases of flight and all airspace users (including drones) and would mean the same setting could be used across the entire airspace where an aircraft operates. The main benefit is that the indicated altitude would no longer be affected by meteorological and environmental conditions potentially allowing an increase in safety and in airspace capacity by reducing vertical separation minima.

Next steps

Whist the study has shown that there are no regulatory obstacles preventing implementation in terms of the delivery of the service (who provides it and with what responsibilities and limits of competence), it has identified a number of constraints and pre-requisites which need to be resolved before implementation is possible. The study has provided a broad evolutionary framework for further analysis and evaluation of these issues. However, it is worth emphasising that the decision to move to one or another of these services may also require additional technical developments on the EGNOS side.

It is expected that additional projects will need to be launched to assess the impact of these technical changes and their impact on the proposed roadmap for the evolution of EGNOS services to aviation. The balance and compatibility of the changes needed for these services between the EGNOS system and that on the existing aviation architecture remain open for further evaluation and specification.

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