Loss or Disruption of GNSS signals – Continued operations in a degraded environment

There has been significant discussion on the vulnerabilities of GNSS and encouragement for States to develop appropriate contingency procedures to managed the airspace if the signals from the primary navigation infrastructure suffer degradation.  To raise the awareness of this challenge, EUROCONTROL regularly publishes the observed GNSS degradation across the network on the CNS dashboard which can be accessed here.

A study of European air traffic controllers in 2020 indicated that a significant proportion of the cadre were unaware, did not have or did not know local contingency procedures in the event that the GNSS signals were degraded or lost.  This information led EUROCONTROL to develop and publish the ‘European GNSS Contingency/Reversion Handbook for PBN Operations’ (PBN Handbook No. 6).

As controllers and pilots have clearly defined procedures for the loss of surveillance, loss of comm, blocked runways and even poor weather, one could ask why they do not have the same for the loss of navigation signals.  Developing such contingency procedures will require each State and its service provider(s) to assess how they will manage their traffic in a degraded environment.  One of the key elements in this decision making process will be the reversion infrastructure to support future operations be they PBN or conventional.  The availability and coverage of this reversionary infrastructure will be key to enabling traffic flow to continue if satellite signals are degraded or lost; the DEMETER tool supports this assessment.

In evolving these contingency operations, the States must make a series of decisions on how they plan to operate without the use of GNSS.  To that end, under the Operational Excellence Programme (OEP), a web-based strategic planning tool has been developed to support decision making at ANSP level.  It is hoped that individual ANSPs will use to review the different options offered within the tool and decide which option best suits their operations and enabling a wider European harmonised reversion strategy to be defined. Once this strategic position is established locally, it should then be possible to identify the required reversionary infrastructure needed to support the planned contingency procedures. These contingency procedures for the management of aircraft in a degraded navigation environment will need to be developed and published at local ATCU level. Once the contingency procedures have been agreed with all the involved stakeholders, then the infrastructure managers can plan the placement of future ground-based navigation aids and, more importantly, rationalise those systems that no longer support operations in the degraded environment.  The GNSS Reversion Strategic Decision Making tool can be found here.

Allied to the GNSS Reversion Decision Making tool, EUROCONTROL has also developed a web-based tool for assessing GNSS threats to aircraft operations.

The objective of this GNSS Threat Assessment tool is to allow the individual States and service providers to assess the risk to their operations from the loss or interruption of the GNSS signals.  A set of pre-defined baseline scenarios have been developed which individual users can review or adjust to mirror their own environment.  It is hoped that this assessment tool will enable States to draw up a framework of high-risk threats and enable each State to define appropriate mitigation actions to ensure that operations are managed safely in a degraded navigational environment.  Access to the GNSS Threat Assessment tool can be found here.

It should be noted that while EUROCONTROL has developed both these web-based tools to support the Member States and their associated ANSPs, the Agency takes no responsibility (and equally has no liability) for the decisions taken using either the Decision Making or Threat Assessment tools.

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