Moving from GPS towards a multi-constellation GNSS

11 April 2017

In December 2016, the International Civil Aviation Organization (ICAO) Navigation System Panel (NSP) adopted a working paper presented by EUROCONTROL, containing an initial version of the Concept of Operations (CONOPS) for the use of the next generation Global Navigation Satellite System (GNSS) in aviation.


The Global Positioning System (GPS) offers a single frequency service that is being used by many systems and applications in aviation such as performance-based navigation (PBN) or automatic dependent surveillance-broadcast (ADS-B). The next generation GNSS will offer dual frequency services provided by modernised GPS as well as other constellations such as GLONASS (developed by the Russian Federation), Galileo (being developed by Europe), and BDS (being developed by China). The dual frequency multi-constellation (DFMC) capability will provide enhanced performance which should bring operational benefits to users. 

CONOPS: objectives and challenges

Following the recommendations of the ICAO 12th Air Navigation Conference in 2012, the ICAO NSP is preparing this CONOPS to build consensus on how the next generation GNSS will be introduced in ATM in a cost-efficient manner to bring operational benefits while addressing identified technical, operational, political and institutional challenges. That means finding the simplest way to bring benefits to users, while keeping global interoperability and without making the system too complex or expensive.

The challenge of the CONOPS is to manage the conflicting interests of several stakeholders. The United States, Europe, China and Russia want their systems to be used by aviation. ICAO States have to publish which GNSS element can be used in their airspace. On the one hand, the requirements from States and the need to process more GNSS signals imply more complex avionics, but on the other hand, airlines and industry want to transition to the next generation GNSS with minimum impact in terms of additional costs and complexity.

EUROCONTROL is playing an instrumental role in drafting the CONOPS, acting as facilitator in trying to accommodate and align stakeholders’ different interests.

 “We are working within ICAO because having an interoperable solution worldwide is a must. Today, GNSS is based on one constellation and one frequency, GPS L1; it is a very simple solution and it works. But if for some reason it fails or is not available, it could have a significant impact on capacity. We want to improve robustness and bring benefits to users, but without making it too complex,” points out Paco Salabert from the Navigation Unit at EUROCONTROL. 

 “The big challenge is to satisfy all stakeholders. We are facilitating an agreement between the States’ interests and views, while respecting the interests of airlines and industry,” explains Ken Ashton who is working for EUROCONTROL on the CONOPS.

This Concept of Operations includes a preliminary, high-level implementation timeline covering GNSS system developments, standardisation, receivers’ certification, approval of the use of GNSS elements by States and operational implementation in air traffic management (ATM). The operational introduction of dual-frequency multi-constellation GNSS could start in the 2025-2028 timeframe.

Next steps

The initial CONOPS document was presented to the ICAO Air Navigation Commission and is being distributed for consultation to Member States, several ICAO groups and panels, airspace users, air navigation service providers, industry, the European Organisation for Civil Aviation Equipment (EUROCAE), the Radio Technical Commission for Aeronautics (RTCA) and other stakeholders.

EUROCONTROL is coordinating inputs to the CONOPS working in partnership with European stakeholders including States, air navigation service providers, industry, airspace users, the European Commission, the European Aviation Safety Agency (EASA), the European GNSS Agency (GSA) and the European Space Agency (ESA). Additionally, there is a task in the Single European Sky ATM Research (SESAR) 2020 to further develop European contributions to the CONOPS. It is expected that a new version, one that will be based on feedback and input received, will be adopted by ICAO NSP in October 2017.

It is planned to present the CONOPS at the ICAO Global Air Navigation Industry Symposium (GANIS) event in December 2017. An ICAO secretariat paper on the subject should be tabled at the 13th Air Navigation Conference that will take place in 2018.

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