GPS, the global positioning system that underpins everything from Google maps to telecommunication networks and aviation navigation, has become unreliable across huge stretches of the Mediterranean, Caucasus and the Middle East, as geopolitical tensions have risen in the region, according to the European agency responsible for safe air traffic management.

Air traffic experts worry that a prolonged disruption to GPS could put the safety of commercial airline passengers at risk.

Reports of GPS outages submitted by pilots from the cockpits of commercial flights show that disruptions to the navigation system, which was created and is maintained by the U.S. government, are now standard occurrence on the flight routes between North America and Europe and the Middle East, according to data from the European Organization for the Safety of Air Navigation, known as Eurocontrol.

In 2019, the regulator received more than 3,500 reports of outages, an all time high, according to Gerhard Berz, the senior expert for navigation systems and radio spectrum coordination at the agency. That worked out to an average of about 10 reports per day throughout 2019 being reported to the agency.

This year, the sharp decline in air traffic due to the global pandemic means that fewer planes are flying, and so there's less visibility into how common disruptions are, Berz says. Even still, the agency is receiving at least one report per day of outages, he says. Because reporting outages is entirely voluntary, the full scale of the disruption is expected to be far higher than the figures suggest.

Although the outages are assumed to be a knock-on effect from conflict zones and militaries on the ground, their sheer scale means it's not clear who is responsible for all of the outages, according to experts. The leading assumptions from experts in the area is they come from military operations from multiple countries in the region, including airbases and vessels—in the East Mediterranean, one of the rare examples where public attribution has been made, such outages have been traced to an airbase on the coast of Syria. Berz says the fact that the outages are intermittent and not continuous, and therefore difficult to predict, makes it even harder to trace the disruptions to their exact source.

In several cases, those outages had strange and potentially dangerous implications, including several instances where confusion to the GPS systems triggered a warning from the plane’s Ground Proximity Warning System, which warns a pilot they are about to hit land or an obstacle and must immediately “pull up” the nose of the plane to avoid crashing. Such warnings are usually worst-case scenarios. In these cases, they were false alarms that were correctly ignored by the pilots, who could see their locations clearly, said Berz.

But requiring pilots to selectively ignore urgent safety warnings goes against their training that such an alarm is a key safety net when ground control has failed, and should never be ignored, he said.

“We don’t like when confidence in those systems is undermined,” Berz says.

Flying blind

In other cases, GPS receivers that were disrupted while flying through the region did not regain a signal again until after leaving the disrupted region, said Berz, requiring pilots to fly for hours without the GPS system.

Commercial planes have multiple systems for navigation and communication—GPS is just one. That means that losing GPS, especially for short periods, is not necessarily dangerous, and pilots can function without it. However, Berz warned that it is the “sheer magnitude” of the disruptions that is worrying, because it raises the risk that a disruption could line up with a failure of other key equipment, or that in dark or stormy weather it may be harder to use other cues to navigate.

There is also the added risk in areas where geopolitical tension is high. And for the few flights passing between Europe and the Middle East, including enroute to Asia, traveling through such risky region is unavoidable. Because Syrian airspace is closed, planes must fly either south of Syria through the Mediterranean, or north, through Turkey and the Caucasus. Both routes see regular reports of outages, Berz said. The area affected includes spill-over from the Syrian war, an ongoing conflict in Libya, and the recent explosion of tensions between Armenia and Azerbaijan, to name but a few.

Cyprus, in particular, has struggled with persistent outages for years now, affecting both maritime and air traffic, as Fortune reported in January as part of a series on the impact of disrupted GPS on the maritime sector.

The country has repeatedly put out official government aviation warnings of GPS interference throughout 2020, via its department of civil aviation. The U.S. Coast Guard, meanwhile, reports the disruptions extend into the Mediterranean Sea as far Northwest as Italy.

The risks of such widespread disruption has gradually gained more and more attention in the sector. In August, the UN's aviation agency, the International Civil Aviation Organization (ICAO), passed a proposal recognizing the impact of "harmful interference" to GPS, and suggested a range of actions to address it. That included encouraging members to develop contingency systems for GPS failure, and to support alternatives to GPS; address the sale of illegal "jammers"; and recognize that risks to GPS from conflict zones can spill beyond the affected area.

It is difficult to overstate the ubiquity of GPS in both military and civilian life. On-land GPS receivers transmit precise time and location data of vital infrastructure for our data-driven economy, a level of accuracy that is used to sync everything from global telecommunications networks, to banking transactions and ATMs, to stop lights and energy management systems.

Saboteurs

GPS disruptions can be caused by weather, user equipment or by other innocuous reasons. But the disruptions of the scale seen over parts of the Mediterranean and Middle East are believed to be largely caused by intentional “jamming” and “spoofing,” two techniques used to disrupt or confuse signals sent from GPS satellites to receivers on earth. Though GPS is only one of several satellite global navigation systems—China, Russia and the EU all have comparable networks—GPS is the most widely used globally, and all such systems (collectively known by the acronym GNSS) are vulnerable to disruptions.

Although regular people, small operations and criminal networks, equipped with illegal jammers bought online, can and do regularly cause chaos to GPS signals, the scale of the disruption in the Mediterranean, central Asia and Middle East is believed to be the work of militaries and state actors, according to analysts and industry experts who specialize in GPS systems. NATO's Shipping Centre, which liaises with commercial shipping, has repeatedly linked such disruptions in the Med to nearby conflict zones.

For militaries and state actors, of GPS disruption is both a classic form of electro-magnetic warfare—after all, disrupting communications and navigation has always been part of conflict. But it is also part of a new form of wide scale, grey-area disruption that has gained pace in the last five to six years as drones and other GPS-directed surveillance and weaponry has become an increasing part of conflict.

However, the total extent of the disruptions globally is far too large to be attributed to just one actor. Rings of spoofing, nicknamed “crop circles” have been tracked to ports in China and to bizarre locations off the coast of San Francisco, according to investigations by Bjorn Bergman at the NGO SkyTruth. And such disruptions are a feature of life near the coast of North Korea, where illegal fishing fleets reportedly operate on a huge scale. Such disruptions have also been tracked at a more local level: in late 2019, small circles of GPS disruption affecting mobile phones began to appear in central Tehran, according to a report made to the U.S. Coast Guard and provided to Fortune.