Drone Down: Someone’s Messing with Satnav Signals over Protest-Hit Serbia

On May 23 this year, drone enthusiast Novak [not his real name] launched a Chinese-made drone into the sky over Belgrade’s Salvija Square, where tens of thousands of people were gathered in protest against Serbia’s ruling Progressive Party. Novak, xx, used the drone, manufactured by the Chinese technology firm DJI, to take aerial photos of the protest, the latest against authorities under President Aleksandar Vucic since a concrete canopy at a newly renovated railway station in northern Serbia collapsed in November 2024, killing 16 people. At 2.35 p.m., however, something strange occurred. For a period of 13 minutes, Novak’s drone lost all contact with the satellites it used to navigate its way and switched from automatic mode to semi-manual. Finally, the drone picked up a signal falsely indicating it was flying over Belgrade’s Nikola Tesla Airport, where drones are strictly forbidden. “The signal places you at the airport or somewhere similar, so it effectively forces your drone to land,” he recalled. “The drone thinks it’s in a prohibited flight zone and tells itself, ‘Right, I’m not allowed to fly here’, and lands.” Such incidents have been occurring in Serbia for years, and often coincide with major anti-government rallies, elections, or other politically sensitive events. According to the findings of this investigation, there have been at least 25 cases of interference in satellite signals over Serbia in the past four years, ranging from deliberate jamming to the transmission of false data, known as ‘spoofing’. BIRN based its findings on data gathered from two global monitoring platforms – GPSJam and GPSwise – that collate and analyse aircraft-derived satellite signals used in geospatial positioning, navigation, and timing under the umbrella term Global Navigation Satellite System, GNSS. Fourteen of the incidents identified in the data most likely originated within Serbia, but at least 11 could be traced to Ukraine and Serbia’s neighbours Romania and Bulgaria. Occasionally, fake signals transmitted from sources in Serbia disrupted the flight course of aircraft more than 100 kilometres away. The transmission of fake signals can be highly dangerous for any system that relies on satellite navigation, such as GPS, within the affected area. “This technology is primarily intended for security agencies. It is not something that anyone can buy – that would be illegal,” said Álvaro Díaz Patricio, co-founder of Zero Industries, which develops navigation solutions for drones. “When you use this technique, the goal is not simply to disable the satellite navigation system. On the contrary, the system continues to believe it is receiving a valid GPS signal.” “You are not telling it that it has lost GPS; you are making it believe false data. That is extremely dangerous. Frankly, I do not see many legitimate uses for transmitting false navigation data.” Serbia’s Regulatory Authority for Electronic Communications and Postal Services, RATEL, provided BIRN with details of complaints it had received regarding the interference but said it had not itself registered any harmful disruption. RATEL rejected part of BIRN’s Freedom of Information request concerning notifications of interference issued by Serbia’s interior ministry, the intelligence agency BIA, and the military. Serbia’s air traffic control agency, SMATSA, and the Civil Aviation Directorate refused to provide any information concerning reports of interference submitted by airline pilots. ‘Something was going on’ On May 23 this year, drone enthusiast Novak [not his real name] launched a Chinese-made drone into the sky over Belgrade’s Salvija Square, where tens of thousands of people were gathered in protest against Serbia’s ruling Progressive Party. Novak, xx, used the drone, manufactured by the Chinese technology firm DJI, to take aerial photos of the protest, the latest against authorities under President Aleksandar Vucic since a concrete canopy at a newly renovated railway station in northern Serbia collapsed in November 2024, killing 16 people. At 2.35 p.m., however, something strange occurred. For a period of 13 minutes, Novak’s drone lost all contact with the satellites it used to navigate its way and switched from automatic mode to semi-manual. Finally, the drone picked up a signal falsely indicating it was flying over Belgrade’s Nikola Tesla Airport, where drones are strictly forbidden. “The signal places you at the airport or somewhere similar, so it effectively forces your drone to land,” he recalled. “The drone thinks it’s in a prohibited flight zone and tells itself, ‘Right, I’m not allowed to fly here’, and lands.” Such incidents have been occurring in Serbia for years, and often coincide with major anti-government rallies, elections, or other politically sensitive events. According to the findings of this investigation, there have been at least 25 cases of interference in satellite signals over Serbia in the past four years, ranging from deliberate jamming to the transmission of false data, known as ‘spoofing’. BIRN based its findings on data gathered from two global monitoring platforms – GPSJam and GPSwise – that collate and analyse aircraft-derived satellite signals used in geospatial positioning, navigation, and timing under the umbrella term Global Navigation Satellite System, GNSS. Fourteen of the incidents identified in the data most likely originated within Serbia, but at least 11 could be traced to Ukraine and Serbia’s neighbours Romania and Bulgaria. Occasionally, fake signals transmitted from sources in Serbia disrupted the flight course of aircraft more than 100 kilometres away. The transmission of fake signals can be highly dangerous for any system that relies on satellite navigation, such as GPS, within the affected area. “This technology is primarily intended for security agencies. It is not something that anyone can buy – that would be illegal,” said Álvaro Díaz Patricio, co-founder of Zero Industries, which develops navigation solutions for drones. “When you use this technique, the goal is not simply to disable the satellite navigation system. On the contrary, the system continues to believe it is receiving a valid GPS signal.” “You are not telling it that it has lost GPS; you are making it believe false data. That is extremely dangerous. Frankly, I do not see many legitimate uses for transmitting false navigation data.” Serbia’s Regulatory Authority for Electronic Communications and Postal Services, RATEL, provided BIRN with details of complaints it had received regarding the interference but said it had not itself registered any harmful disruption. RATEL rejected part of BIRN’s Freedom of Information request concerning notifications of interference issued by Serbia’s interior ministry, the intelligence agency BIA, and the military. Serbia’s air traffic control agency, SMATSA, and the Civil Aviation Directorate refused to provide any information concerning reports of interference submitted by airline pilots. ‘Something was going on’ GNSS comprises four major networks: US Global Positioning System, or GPS, the European Union’s Galileo, Russia’s GLONASS, and China’s BeiDou. They form a critical part of modern infrastructure. Besides guiding aircrafts, ships and vehicles, such systems are used in the energy sector, telecommunications, geodesy, maritime navigation, precision agriculture and numerous industrial systems that depend on accurate positioning and timing. “It is used by almost every sector of industry,” said a radio frequency and telecommunications expert in Serbia, speaking on condition of anonymity. “Interference can lead to the collapse of transport, the failure of telecommunications networks, problems in banking systems, while emergency services lose the ability to locate incidents quickly.” The protest Novak took photos of, in May, wasn’t the only one where jamming and spoofing were detected. Data from GPSwise and GPSJam show both phenomena occurred between 1 p.m. and 5 p.m. on March 15, 2025, when Serbia witnessed one of the biggest anti-government protests in its history. According to GPSwise data, fake satellite signals affected several commercial flights, including Pegasus Airlines flights from Paris to Istanbul, London to Istanbul and Amsterdam to Istanbul, a Smartwings Hungary flight from Budapest to Egypt, and Wizz Air flights from Catania, southern Italy, to Warsaw and from Brussels to Craiova, Romania. A source with expertise in the civil aviation sector, who spoke on condition of anonymity, said pilots landing at Nikola Tesla Airport also reported navigation interference. “What I know is that the largest number of problems coincided with March 15,” the source told BIRN. “That was when the highest number of reports came in. Five, six, seven aircraft reported problems – it was obvious that something was going on.” One Wizz Air flight received false navigation data while it was still over Hungary, approximately 250 kilometres from the source of the interference in Belgrade. The Pegasus flight from Paris to Istanbul was over Krupanj, some 100 kilometres southwest of Belgrade, when it encountered the same problem. “Since GNSS signals are not selective, interfering with one drone also affects all other systems within a radius ranging from several hundred metres to several kilometres,” said the radio frequency and telecommunications expert. “Their disruption is justified only in extreme security situations.” “The operational range of such systems can be quite extensive, and to maximise effectiveness, jamming systems generally operate at maximum transmitter power,” “The aircraft detect lower-intensity interference because each directional jamming beam can still be detected at much lower intensity over considerable distances, particularly in airspace.” The source with civil aviation expertise said that, while aircraft have other navigation systems, they “primarily rely on GNSS” when approaching airports. “Today, pilots generally do not fly aircraft manually but rely on computers, whose most important requirement is to know the aircraft’s precise position at all times,” the source told BIRN. “All major airports, including Belgrade, have precision approach procedures that require certain standards to be met, including reliable satellite navigation. Without it, that level of precision is significantly reduced.” If navigation systems are disrupted, pilots are obliged to make a report, he said. Drones grounded Photo:During the May 23 protest, Novak’s drone registered several instances of interference: at 2.35 p.m., 6.30 p..m. and 7.30 p.m. It happened again at around 8.30 p.m., as protesters and police clashed. “In the evening it became a much bigger problem,” Novak told BIRN. “Once the clashes started near the National Assembly and the Constitutional Court, you would be flying normally with three satellite connections, and then within two and a half seconds they would all drop to zero.” Novak is convinced the aim was to prevent drones from documenting the protest, but it risked bringing them down on the heads of protesters. One opposition activist, who was also flying drones that day, said that around 10 were in the air over Slavija Square and all of them were forced to land. RATEL received a complaint of interference that day but the regulator said it had not detected any disruption. Patricio, of Zero Industries, said a jammer resembles an “antenna”. “The higher it is installed, usually on top of a building, the larger the area it can cover,” he told BIRN. “Estimating the exact coverage area is not straightforward because the signal spreads between buildings, reflects and propagates in ways that are difficult to predict. A radius of around 30 kilometres is generally considered standard.” Spoofing is more advanced than interference, he said, and the potential consequences far less predictable. “When jamming occurs, the GPS signal is lost and systems are generally designed to cope with that. When you enter a tunnel or a similar environment, the system must be prepared for a temporary loss of GPS. However, systems are not designed to deal with a situation in which they can no longer trust the GPS signal itself. When the system changes its perceived location and believes you are somewhere else, we do not know exactly what could happen.” Regulator: No interference detected Photo:Some of the complaints received by RATEL were submitted on the same days that GPSJam and GPSwise registered interference, e.g. October 11, 2025, the day before local elections in Serbia’s former southern province, Kosovo; and July 6 this year, when there was a complaint of “GPS interference from Avala [mountain overlooking Belgrade] towards Belgrade Airport”. Again, in reference to the July 6 complaint, RATEL said it had not detected interference, though it stressed that its recording stations at Belgrade Airport and the Belgrade district of Makis were out of service at the time. The radio frequency expert said RATEL’s mobile and stationary monitoring stations allow it to monitor “almost” the entire territory of Serbia. “Once interference is detected, it is obliged to take all necessary measures to identify the transmitter and the perpetrator, seize the equipment and ensure that the offender is sanctioned,” the expert told BIRN. “If the interference is carried out by agencies authorised to do so, RATEL does not intervene.” GPSJam and GPSwise did not pick up every incident of interference reported to RATEL. One, dated May 19 this year, cited “GNSS spoofing during a flight from the tri-border area of Serbia, Croatia and Hungary to Belgrade”; another reported GPS jamming for a duration of two minutes on July 2 on the “Belgrade–Vienna route, in the area of Vojka and Stara Pazova [northwest of Belgrade]”, again suggesting the complaint originated from a pilot. The sources of the complaints were not revealed in the information provided to BIRN. Fake signals were also reported on May 22 and October 17 last year in the Kraljevo area of central Serbia and the Belgrade area respectively. With the exception of countries bordering Russia, Ukraine, and Belarus, continental Europe is generally coloured green on GPSJam’s map of satellite navigation interference, meaning incidents are very rare. Isolated cases have, nevertheless, been identified around several major cities besides Belgrade, including Rome, Naples, Edinburgh, Athens, and Monaco. Tirana has also seen an uptick in interference since the start of anti-government protests in early June. Satellite navigation interference has become a regular occurrence in Ukraine and its immediate neighbourhood since Russia launched its full-scale invasion in February 2022. The effect was also felt in Serbia, Hungary, Slovakia and the Czech Republic, where GPSJam and GPSwise data show flights were falsely redirected to Lima, Peru. Patricio said this may be the result of a single navigation message, such as a latitude or longitude coordinate, being altered, causing the navigation system to “jump” to the opposite side of the planet. On May 13 this year, two flights near Belgrade were affected by fake signals, switching their displayed location to somewhere near Skopje, North Macedonia. On the same day, RATEL received a report that several flights operating between Serbia and Hungary had been affected, but said it had not detected any harmful interference. Serbia’s military held exercises that day in the north of the country. The fact the location display switched to Skopje suggested the source of the interference was within Serbia or somewhere nearby. On May 23 this year, drone enthusiast Novak [not his real name] launched a Chinese-made drone into the sky over Belgrade’s Salvija Square, where tens of thousands of people were gathered in protest against Serbia’s ruling Progressive Party. Novak, xx, used the drone, manufactured by the Chinese technology firm DJI, to take aerial photos of the protest, the latest against authorities under President Aleksandar Vucic since a concrete canopy at a newly renovated railway station in northern Serbia collapsed in November 2024, killing 16 people. At 2.35 p.m., however, something strange occurred. For a period of 13 minutes, Novak’s drone lost all contact with the satellites it used to navigate its way and switched from automatic mode to semi-manual. Finally, the drone picked up a signal falsely indicating it was flying over Belgrade’s Nikola Tesla Airport, where drones are strictly forbidden. “The signal places you at the airport or somewhere similar, so it effectively forces your drone to land,” he recalled. “The drone thinks it’s in a prohibited flight zone and tells itself, ‘Right, I’m not allowed to fly here’, and lands.” Such incidents have been occurring in Serbia for years, and often coincide with major anti-government rallies, elections, or other politically sensitive events. According to the findings of this investigation, there have been at least 25 cases of interference in satellite signals over Serbia in the past four years, ranging from deliberate jamming to the transmission of false data, known as ‘spoofing’. BIRN based its findings on data gathered from two global monitoring platforms – GPSJam and GPSwise – that collate and analyse aircraft-derived satellite signals used in geospatial positioning, navigation, and timing under the umbrella term Global Navigation Satellite System, GNSS. Fourteen of the incidents identified in the data most likely originated within Serbia, but at least 11 could be traced to Ukraine and Serbia’s neighbours Romania and Bulgaria. Occasionally, fake signals transmitted from sources in Serbia disrupted the flight course of aircraft more than 100 kilometres away. The transmission of fake signals can be highly dangerous for any system that relies on satellite navigation, such as GPS, within the affected area. “This technology is primarily intended for security agencies. It is not something that anyone can buy – that would be illegal,” said Álvaro Díaz Patricio, co-founder of Zero Industries, which develops navigation solutions for drones. “When you use this technique, the goal is not simply to disable the satellite navigation system. On the contrary, the system continues to believe it is receiving a valid GPS signal.” “You are not telling it that it has lost GPS; you are making it believe false data. That is extremely dangerous. Frankly, I do not see many legitimate uses for transmitting false navigation data.” Serbia’s Regulatory Authority for Electronic Communications and Postal Services, RATEL, provided BIRN with details of complaints it had received regarding the interference but said it had not itself registered any harmful disruption. RATEL rejected part of BIRN’s Freedom of Information request concerning notifications of interference issued by Serbia’s interior ministry, the intelligence agency BIA, and the military. Serbia’s air traffic control agency, SMATSA, and the Civil Aviation Directorate refused to provide any information concerning reports of interference submitted by airline pilots. ‘Something was going on’