GNSS Reversion Strategic Decision Making


This GNSS Reversion planning tool has been designed to support State and ANSP planners in considering the possible options if a GNSS outage occurs or if the signals from space are unreliable or unusable.  The tool was evolved during the development of a European GNSS Reversion Strategy Discussion paper under the auspices of the Operation Excellency Programme (OEP); however, it can be used without reference to that document. Whilst the European-wide harmonisation of the GNSS reversion strategy is currently beyond the scope of the work undertaken to date, this tool is designed to inform the processes that will perform this harmonisation.  To ensure alignment with the discussion document, the Scenarios are described in the text of each option.

It must be understood that this tool is designed to lead the user to a possible solution for handling the current and future traffic load, based on a planned operational concept for managing the airspace in a degraded Navigation Infrastructure environment.

There are no right or wrong answers and whilst the path the user takes will always end in a solution, the answer is not definitive and EUROCONTROL takes no responsibility (and equally has no liability) for the decisions taken based on the outcome of this tool.

As you work through a particular operational scenario, the options you select will be displayed to you and when a solution is provided, then you can print that list.  This capability will provide the user with the option of reviewing a range of scenarios to see which best matches the needs of the airspace.

Select from the options below your planned strategy for managing the traffic through your airspace when the GNSS signals are unavailable.

Place all aircraft on the ground as soon as possible and stop further operations.

In the OEP Discussion paper, this option relates to Scenario 1:’Tap Full off’.  No traffic is planned to flow at all. Capacity restrictions will be applied, and operations will cease once the aircraft are either on the ground or have been passed onto the next unaffected ATC unit. A zero traffic flow is applied in the affected airspace until GNSS services are restored, then full operations will gradually resume. However, it might be that if the unavailability of GNSS core constellation service were to last longer than several hours, the State might seek, or be encouraged,  to restart operations in the degraded environment.





Continue full operations with no capacity impact.

In the OEP Discussion paper, this option relates to Scenario 2: ‘Tap full on’.  No reduction in traffic flow at all and, where applicable, all PBN operations are free to continue unabated. The State or Service Provider can safely maintain the same level of service and throughput of traffic through its airspace.  As there is no impact on the flow of traffic, no capacity restrictions are applied within the State’s airspace by the service provider and full operations are enabled. The key requirement to achieve this is a reversion infrastructure capable of supporting the Navigation Applications.  Where PBN cannot be supported then a defined infrastructure, together with published procedures and personnel to support full operations within the affected airspace without compromising safety, no matter the duration, nature of the GNSS failure mode or the size of the affected area.






Reduce flow to maintain a level of PBN operations.

Reduce flow to maintain a level of PBN operations.  In the OEP Discussion paper, this option relates to Scenario 3: ‘Tap partially closed’.  A reduction in traffic flow to manage aircraft through the affected airspace. The State or Service Provider will limit capacity to maintain a safe throughput of traffic through its airspace. Capacity restrictions are applied, and operations are limited. Depending on the nature and duration of GNSS failure mode as well as the size of the affected area, infrastructure, procedures and personnel will enable limited operations without compromising safety within the affected airspace. Depending on the root cause of the failure as well as the size of the affected area, whenever safety is considered to be compromised, the State or provider may consider ceasing operations. Full operations will be gradually resumed once GNSS services are restored.








GNSS available? Move to recovery phase
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