Aviation operations, including navigation, surveillance and timing, rely more and more on GNSS services. Concerning navigation, ICAO has decided on the objective to move from ground radio navigation aids based operations to GNSS based operations for all phases of flight. GNSS is already widely used for the cruise part of the flight and is being further developed for the approach and landing operations. The surveillance domain follows the same trend. GNSS based services already enhance radar systems and an increasing part of the surveillance domain will rely on GNSS services in the coming years. A less familiar but still very important application is the use of GNSS as a time reference. GNSS is already used for some radar and multilateration synchronization and an increasing number of networks will rely on GNSS time. GNSS performances under nominal ionosphere condition are already well known. However, before moving further on these GNSS services, the aviation community has to better assess GNSS performances under abnormal ionosphere conditions. EUROCONTROL launched a study in 2009 to assess the impact of the ionosphere on the ECAC GNSS aviation operations. Using existing GNSS ground station networks (IGS, EGNOS, EDCN, EUREF...), the ionosphere is going to be monitored during the next period of maximum solar activity. These ionosphere measurements will be used to confirm the ionosphere threat model developed for the GBAS application but also to model the ionosphere events that may impact the other GNSS services. These threat models will be applied to the characteristics of the current and future GNSS receivers and the impact of the ionosphere on the GNSS performances will be assessed. Then, the GNSS performance degradation will be compared to the aviation operation requirements. Some mitigations means, internal or external to the GNSS receiver will also be evaluated.
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