Increased GNSS interference affecting air traffic

The Reykjavík Control Area

Most aircraft rely on GNSS (Global Navigation Satellite System). GNSS uses satellite signal to determine aircraft’s position. GPS, Galileo, GLONASS and BeiDou are examples of GNSS.

In the year 2023 a significant increase in GNSS jamming and spoofing was reported in aircraft. The most affected regions are the Black Sea area, south and eastern Mediterranean area, The Baltic Sea and the Arctic Sea.

GNSS jamming

When GNSS is jammed the jammer sends out a signal designed to interfere with signal from satellites. Any equipment using a satellite signal to determine a location or time, including aircraft, will then be affected and the GNSS location might become unreliable.

To be able to use GNSS for navigation aboard an aircraft the quality of the GNSS data must be sufficient and the aircraft must be able to receive data from a minimum number of satellites. During GNSS jamming the aircraft must rely on alternative means of navigation such as VOR/DME.

GNSS spoofing

Another type of GNSS interference is spoofing. A spoofer will send out a false signal pretending to be a satellite. The actual position of the aircraft may then be different from the position displayed to the pilot or used by the avionics. In some cases, the pilot might not notice an anomaly and the aircraft could drift off course. Ground base surveillance systems like radars and MLAT systems do not rely on GNSS and would be able to detect the actual position of the aircraft to alert air traffic controllers of a deviation.

ADS-B and ADS-C are, however, dependent on GNSS and those systems would report the incorrect spoofed position to air traffic controllers.

GNSS interference in Reykjavik CTA

There have been no reports of GNSS interference in Reykjavik CTA. The areas mentioned above are subject to constant interference and that affect aircraft navigation in the areas.

Isavia ANS has noticed a significant increase of aircraft in Reykjavik CTA with degraded navigation capabilities after having been subject to GNSS interference earlier in the flight. The interference often occurred hours before the aircraft entered Reykjavik CTA. The indications observed by Isavia ANS are:

· ADS-B data either not transmitted by the aircraft or transmitted with low quality indicators.

· ADS-C reports include low Figure of Merit (FOM).

· Aircraft are unable to log on to datalink (CPDLC), most likely due to incorrect clock on-board the aircraft.

The environment in the NAT region has dramatically changed in recent years with Data Link Mandate and PBCS implementation. All that aims to decrease separation between aircraft allowing more aircraft to fly the optimum route at the optimum flight level (altitude). That leads to less fuel consumption and less cost for airlines.

Those improvements are dependent on reliable GNSS data on-board the aircraft. When aircraft enter the North Atlantic Ocean with degraded navigation capabilities following GNSS interference, then air traffic controllers are no longer able to provide this separation for the aircraft. There are examples of aircraft having to accept reroutes and level changes on account of GNSS interference earlier in the flight.

Number of occurrences

Isavia ANS observed more than 1000 flights in the year 2023 with signs of GNSS interference earlier in the flight (only enroute aircraft). The following chart shows a significant increase starting in June.

What to do?

European Union Aviation Safety Agency (EASA) has issued a Safety Information Bulletin (SIB) regarding GNSS outage and alterations leading to navigation/surveillance degradation ( The SIB includes recommendations for Civil Aviation Administrations (CAA), Air Navigation Servise Providers (ANSP), aircraft operators and equipment manufacturers. The recommendations for ANSPs are as follows:

· Collect information on GNSS degradations.

· Assess the impact of loss or anomalies of GNSS-based timing on Communication, Navigation and Surveillance systems.

· Issue NOTAMs to provide relevant information to airspace users.

· Provide reliable surveillance coverage that is resilient to GNSS interference, as well as maintain essential conventional navigation infrastructure operational in support of conventional navigation procedures.

· Ensure that contingency plans include procedures to be followed in case of large-scale GNSS jamming and/or spoofing events.

· Monitor the traffic closely to prevent any deviation from the flight track/route.

Two representatives from Isavia ANS participated in a symposium in Turkey in February 2024 where experts from around the world gathered to share their experiences of GNSS interference. Pilots explained how GNSS interference affects their daily work and how they are observed in the cockpit. One aircraft operator from the Middle East reported that over 100 cases of GNSS interference were reported daily in their operation.

Isavia ANS is committed to providing safe operations to aircraft. Recommendations from EASA are taken seriously and any effects of GNSS interference will be monitored closely. If an interference is observed within Reykjavik Control Area, relevant warnings will be issued to aircraft.