Public GPS interference maps have become an essential awareness tool for tracking GNSS disruptions worldwide. Services like GPSJAM and GPSwise display interference data derived from aircraft broadcasts, helping aviation professionals and infrastructure operators understand where interference events occur. In 2025 alone, analysts documented over 1,500 flights affected by GPS interference daily, with more than 122,000 flights impacted in the first four months of the year, according to industry tracking.

Yet, these powerful visualization tools are frequently misunderstood. The same maps that raise awareness also create dangerous misconceptions when viewers assume they represent ground-level RF conditions or comprehensive threat coverage. This article explains what GNSS interference maps derived from Automatic Dependent Surveillance-Broadcast (ADS-B) data actually measure, why their limitations matter, and how critical infrastructure operators can avoid common interpretation errors that lead to complacency or misallocated resources.

How ADS-B Based GNSS Interference Detection Works

Understanding the data source is essential before interpreting any GPS interference map. Public interference maps rely on various ADS-B data sources, including networks like ADS-B Exchange and OpenSky Network. ADS-B is a surveillance technology where aircraft determine their position using GPS and periodically broadcast it to ground stations and other aircraft.

These maps primarily rely on navigation quality indicators embedded in ADS-B messages, specifically Navigation Integrity Category (NIC) and Navigation Accuracy Category for Position (NACp). When multiple aircraft in the same region simultaneously report degraded accuracy, the system flags a potential jamming zone. This method effectively detects jamming because interference causes measurable signal degradation that aircraft avionics report through these standard parameters.

Different services offer different detection capabilities. GPSJAM aggregates NIC/NACp indicators into hexagonal grids colored by severity, detecting jamming through signal degradation patterns. Their documentation explicitly states that colors represent the percentage of aircraft reporting low navigation accuracy within each hex. GPSwise, developed by SkAI Data Services, uses the OpenSky Network to detect both jamming (via NIC degradation) and spoofing (via trajectory anomalies such as position jumps or aircraft converging on false coordinates). This distinction matters: Jamming detection through signal degradation is well-established, while spoofing detection through trajectory analysis remains more experimental.

Three Common Misconceptions About GNSS Interference Maps

When context is missing, these valuable awareness tools create beliefs that are not just wrong but operationally dangerous. Based on conversations with infrastructure operators and GNSS professionals, three misconceptions recur most frequently:

Misconception 1: “This is Only an Aviation Problem.”

Because interference maps use aircraft as sensors, many observers frame GNSS disruption as exclusively an aviation issue. Pilots deal with it. Airlines reroute. The narrative stops there. This framing dramatically underestimates the threat. Aviation happens to provide a convenient, global measurement network. The aircraft is a sensor platform, not the only affected domain. The National Institute of Standards and Technology (NIST) has documented critical infrastructure dependencies on GPS timing across financial services, telecommunications and electric power sectors. When aircraft detect interference at altitude, the RF environment near the source may be affecting timing servers, cellular base stations, and grid monitoring systems that lack aviation-style navigation redundancy.

Misconception 2: ”We Are Always in Red, But Nothing Happens.”

Infrastructure operators in regions with persistent interference often observe their location marked red on these maps while their systems appear to function normally. The conclusion seems logical: either their systems are resilient, or the threat is exaggerated. Both conclusions can be wrong. The critical distinction is altitude. Aircraft observe a different RF environment than ground receivers. At cruise altitude (8,000 to 12,000 meters), an aircraft antenna has line-of-sight to interference sources over hundreds of kilometers. A ground-level timing receiver with a rooftop antenna may experience completely different conditions due to terrain, buildings and antenna orientation. GPSJAM’s own FAQ addresses this directly: “I live in a red hex and my phone GPS worked” is not a contradiction. It demonstrates that the map does not describe your personal ground-level environment.

Misconception 3: “Planes Aren’t Crashing, So There’s No Real Danger.”

Aviation has redundancy: inertial systems, distance measuring equipment, ground-based navaids, and trained crews. When GPS fails, aircraft can typically continue safely using backup navigation. This resilience creates a dangerous inference: If aviation handles it, the threat must be manageable. The logic inverts causality. If interference is powerful enough to degrade aircraft-reported GNSS integrity at altitude (where signals from the interference source have propagated through long distances and atmospheric attenuation), then the signal power near the source at ground level may be severe. A jammer affecting aircraft at 10 km altitude is projecting substantial RF power. Ground systems in the jammer’s vicinity, particularly those without aviation-grade redundancy, face potentially greater exposure.

What ADS-B Based Maps Cannot Show

Understanding the boundaries of ADS-B based detection helps operators assess what additional monitoring they need. These maps fundamentally cannot show several critical factors.

First, they cannot provide ground-level RF conditions at specific sites. A timing server, RTK base station, or telecom tower experiences local RF propagation that no aircraft flying overhead can measure.

Second, they cannot detect all interference types. Low-power, localized jammers may affect ground systems without triggering aircraft indicators. Academic research on ADS-B detection emphasizes that unknown aircraft installation details, antenna patterns, and fuselage attenuation all affect what aircraft can observe. Because of all these factors, aircraft-based monitoring can detect only high-power interference.

The temporal aggregation also matters. Most maps aggregate data over time windows, meaning a brief but intense interference event can paint a hex red even though GPS functioned normally for most of the day.

The Role of Ground-Based Monitoring

The gap between aircraft-based awareness and ground-level reality highlights a fundamental challenge. Unlike GNSS interference detection based on ADS-B data, ground-based sensors measure the actual RF environment at the location where protection matters.

This is where centralized ground-based monitoring becomes essential. While ADS-B data captures interference visible to aircraft at altitude, 99% of GNSS-dependent infrastructure operates at ground level. Timing servers in data centers, cellular base stations, power grid synchronization units, and financial trading systems all rely on GNSS signals received at ground level, where propagation conditions differ significantly from what aircraft experience at cruise altitude.

Ground-based monitoring sensors installed at critical infrastructure sites measure the actual RF environment where timing and positioning matter. They detect interference that may never reach aircraft antennas, including low-power jammers operating in urban environments or localized interference targeting specific facilities. A centralized monitoring architecture allows operators to correlate events across multiple sites, identify patterns, and respond to interference that aircraft-based systems simply cannot see.

How ADS-B Maps and Ground Monitoring Complement Each Other

ADS-B based maps and ground-level monitoring serve complementary rather than competing functions. A responsible approach treats them as layers in a complete awareness strategy.

ADS-B maps excel at regional awareness. They show where high-power GNSS disruption is occurring at scale, identify recurring hot zones, track the geographic spread of interference events, and build the case for resilience investment with visual evidence that non-specialists can understand.

Ground-level sensors provide site-specific truth. Only a sensor at your location measures the RF environment your systems experience. Ground sensors provide the detection latency, classification accuracy, and historical logging needed for operational response and post-incident analysis.

Correlating both creates complete situational awareness. When an ADS-B map shows your region as active, ground sensors can confirm or refute local impact. When ground sensors detect interference that does not appear on ADS-B maps, you have identified localized activity that aircraft-based systems miss. This correlation capability becomes particularly valuable for post-event analysis and developing mitigation strategies.

Conclusion

The proliferation of GNSS interference maps derived from ADS-B data represents a significant advance in threat awareness. With GPS jamming affecting hundreds of incidents daily in 2025, visibility into the problem has never been greater. But visibility is not protection, and awareness tools become dangerous when they create false confidence.

The core message for infrastructure operators is straightforward. ADS-B based maps show high-power GNSS disruption is occurring, where it recurs, and that the problem is growing. They do not show whether your specific ground-level site is affected, how your timing systems respond, or whether low-power interference is silently degrading your operations.

As GNSS interference transitions from a niche concern to an operational reality affecting aviation, telecom, finance, and energy sectors, the organizations that understand both what these maps show and what they hide will be best positioned to maintain resilient operations. The first step is recognizing that a red hex on a screen is a starting point for investigation, not a conclusion about your specific infrastructure. 

Author

Maksim Barodzka is the CEO and founder of GPSPATRON. Since 2012, he has been active in IT entrepreneurship, with a strong focus on embedded systems, real-time monitoring and RF/GNSS technologies. In 2018, he founded GPSPATRON, a company developing GNSS interference detection and classification systems designed to detect, analyze and support mitigation of sophisticated GNSS jamming and spoofing threats.

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The trial, conducted in June 2026 across multiple UK sites with support from QinetiQ, the Defence Science and Technology Laboratory (DSTL) and the Royal Navy experimentation vessel XV Patrick Blackett, paired Saab’s Giraffe 1X radar with Aquark’s AQlock cold-atom quantum clock. Multiple radars operating at separate locations tracked live targets while relying solely on independent AQlock timing references rather than GPS.

Distributed radar networks depend on timing precision to within billionths of a second to fuse tracking data from separated sensors into a single accurate picture; an error in timing translates directly into an error in target position. GNSS normally supplies that reference, but its signals are vulnerable to jamming and spoofing in contested environments.

To test resilience, the team introduced controlled timing errors simulating GNSS spoofing and denial. According to Saab, the radars continued generating a single air picture throughout, showing predictable performance degradation during the disruption and rapid recovery once synchronization was restored. DSTL functioned as network rebroadcast nodes to distribute the AQlock timing signals across the radar sites.

Saab said it believes the trial to be the first demonstration of a distributed high-performance military radar network maintaining a coherent operational picture using independent quantum timing sources.

“This trial is a great example of how collaboration can accelerate innovation. By combining quantum timing technology with Saab’s advanced Giraffe 1X radar system, we have demonstrated a practical capability that could help customers continue to operate effectively when it matters most,” said Andy Fraser, Group Managing Director at Saab UK.

The trial marks the third collaboration between Aquark and the Royal Navy’s DCTO, following an earlier sea trial in which the AQlock ran continuously aboard HMS Pursuer in the Solent for three days. Aquark’s work under the Royal Navy’s Quantum Optimised Radar project began in December 2025.

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The hub’s mandate includes developing GNSS-independent navigation technologies and spoofing detection capabilities.

“Quantum will shape the next generation of defence capabilities, and Canada must be prepared to lead—not follow,” McGuinty said. “Through the Quantum Defence Innovation Secure Hub, we’re bringing together Canadian researchers, innovators, industry, and government to accelerate Made-in-Canada quantum technologies into mission-ready capabilities that strengthen the operational advantage of the Canadian Armed Forces while growing Canada’s sovereign defence industrial base.”

The Quantum DISH is established under Canada’s Bureau of Research, Engineering and Advanced Leadership in Innovation and Science (BOREALIS), a Department of National Defence framework for connecting government, industry and academic partners on defense innovation. It joins two existing BOREALIS hubs, the Maritime DISH pilot and the Uncrewed Systems DISH, and was selected through a competitive Call for Proposals held from February 18 to April 2, 2026.

GNSS resilience among four focus areas

The hub will organize work around four areas: quantum sensing, quantum communications, quantum algorithms and quantum hardware assurance. According to the Department of National Defence release, the work will support development of GNSS-independent navigation technologies, spoofing detection capabilities, quantum-secure communications and timing, decision-support tools, and testing and validation of quantum devices and systems ahead of deployment. The department said the hub is intended to reduce vulnerabilities in contested environments, including GPS spoofing, and to help maintain Canada’s technological advantage as global competition in quantum-enabled defense technology accelerates.

The consortium’s goal is to deliver validated prototypes to the Canadian Armed Forces and the Communications Security Establishment within two years.

Consortium and operation

The hub will be operated by the University of Calgary’s Quantum City initiative, under managing director Dr. Megan Lee. The 13-member consortium includes Lockheed Martin Canada, General Dynamics Mission Systems Canada, CAE, Dell Canada and Calian, along with academic partners the University of Saskatchewan, University of Alberta and University of Lethbridge, with the Saskatchewan institutions supported by the Sylvia Fedoruk Canadian Centre for Nuclear Innovation.

“Quantum City is uniquely positioned to build the cross-sector partnerships needed to advance quantum technologies for defence,” said Dr. Megan Lee, managing director of Quantum City. “By connecting defence stakeholders with researchers, innovators and industry leaders, the Quantum Defence Innovation Secure Hub will accelerate the development and deployment of quantum solutions to strengthen Canada’s defence and national security capabilities.”

Quantum is designated one of Canada’s sovereign capability priorities under its Defence Industrial Strategy. The Department of National Defence said DISHs are designed to provide secure, mission-oriented environments where trusted partners can collaborate on research, testing and validation of technologies for defense and national security use, addressing what it described as a persistent gap between defense innovation and defense procurement.

Lockheed Martin Canada is among the industry partners in the consortium. “We’re incredibly proud to be a supporting partner of Canada’s Quantum Defence Innovation Secure Hub, helping accelerate the transition of quantum R&D into field-ready capabilities for our Canadian Armed Forces,” said Kristen Leroux, vice-president and regional executive, Lockheed Martin Canada and Latin America. “By combining enterprise-level engineering rigour with the speed of innovation, our Lockheed Martin Canada team is ready and energized to collaborate with our DISH partners, empowering delivery of high-impact quantum technology from the lab to the field.”

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An unusual thing is happening in the navigation community. Almost everyone now believes in low Earth orbit positioning, navigation and timing (LEO PNT). Governments are studying it. Startups are building it. Researchers are publishing it. Investors are funding it. Satellite operators are discussing it (Figure 1). Even the GNSS community, historically cautious about claims of disruption, increasingly accepts that LEO will play some role in the future of PNT.

For years, the central challenge surrounding LEO PNT was whether it could work. Today, that challenge is increasingly getting addressed. Dedicated LEO constellations have transmitted navigation signals from orbit. Opportunistic approaches have demonstrated PNT with signals never intended for navigation. Governments have initiated national LEO PNT programs, while commercial companies are investing billions of dollars in satellite infrastructure that may ultimately support PNT.

LEO PNT is entering an uncomfortable phase of maturity. The debates are shifting from technical to operational. Can LEO PNT be trusted? Can it scale? Can it integrate? Can it survive commercially? Can it become infrastructure? What role will it play? Who will pay for it? And perhaps most importantly, what problem is it actually solving?

The questions are shifting from “Can LEO PNT work?” to “Can LEO PNT become trusted infrastructure?” The answers depend, in part, on which vision of LEO PNT one adopts.

As discussed in last issue’s column, LEO PNT: Why Now?, four schools of thought have emerged: dedicated, dual-purposed, augmented and opportunistic LEO PNT. Each starts from a different premise about what problem LEO should solve and how it should fit into the broader PNT ecosystem.

Dedicated providers such as Xona, TrustPoint, Centispace and others are building navigation-first systems. Dual-purposed systems such as Iridium combine communications and PNT. Augmented architectures, exemplified by ESA’s Celeste vision, view LEO as an additional layer that complements GNSS. Opportunistic approaches exploit them all. Anything that can be tracked is fair game—it becomes a potential navigation source.

Although these four approaches differ substantially in architecture, economics and operational assumptions, they ultimately encounter the same three questions.

QUESTION 1: How Close are We to Operational LEO PNT?

This may be the most misunderstood question in the field. The answer depends on which school of thought you examine.

A dedicated constellation, a dual-purposed communications system, an augmented GNSS architecture, and an opportunistic navigation system do not become operational in the same way. Each follows a different path from demonstration to utility, and each encounters different technical, economic and operational challenges along the way.

This distinction is important because discussions of LEO PNT often treat the field as if it was a single technology moving toward a common destination. In reality, the various LEO PNT approaches may be solving different problems, serving different users, and operating under different definitions of success.

Dedicated systems are transitioning from demonstration to infrastructure. They arguably face the most difficult transition because they must simultaneously build a constellation, a timing architecture, a monitoring network, a receiver ecosystem, and a customer base. Launching satellites is difficult. Building infrastructure that users trust for decades may prove even harder.

Some dual-purposed systems are already operational. Ironically, the school closest to operational maturity may not be the dedicated providers that receive the greatest attention. Iridium PNT already operates from an existing communications infrastructure and currently represents the most mature example of operational LEO PNT. The space segment exists. The ground segment exists. The satellites have demonstrated years of operation. The challenge is, therefore, less about deployment and more about expanding capability.

Augmented systems may face the lowest adoption barrier because they do not need to displace GNSS. Their value proposition is incremental rather than revolutionary. If a LEO layer improves availability, shortens precise point positioning (PPP) convergence, strengthens resilience, or improves urban performance, then it can justify deployment without ever becoming a standalone navigation system.

Opportunistic systems are another beast, presenting a different definition of operational. What does it mean for a navigation system to become operational when the underlying infrastructure belongs to someone else? In one sense, opportunistic systems are already operational because the satellites, signals and user communities already exist. In another sense, they remain developmental because the navigation capability depends on extracting observables from infrastructures whose operators make no formal navigation commitments.

Despite their differences, all four schools eventually encounter the same challenge. Demonstrations answer whether navigation is possible. Operational services answer whether navigation can be trusted.

A single satellite can demonstrate ranging. A handful of satellites can demonstrate positioning. A constellation can demonstrate coverage. But infrastructure requires something more. We should stop asking whether satellites have launched. Instead, we should ask whether orbit determination is operational, whether time synchronization is operational, whether monitoring and integrity frameworks are operational, whether continuity targets are being met, and whether performance commitments are backed by demonstrated capability.

The greatest risk facing many LEO PNT initiatives may no longer be technical failure. It may be the assumption that technical success automatically leads to operational adoption. 

QUESTION 2: What Can One Satellite or a Small Constellation Contribute?

One of the most common misconceptions surrounding LEO PNT is that value emerges only after a constellation achieves continuous global coverage.

History suggests otherwise. Some in the navigation community often think in binary terms. A system is either operational or it is not. A constellation either provides continuous positioning or it does not. Yet, many of the most important capabilities emerge long before full operational capability is reached.

This is not unique to LEO PNT. GPS itself began creating value well before the constellation reached full operational capability. The same was true for communications constellations, Earth observation systems, and timing infrastructures. Early deployments rarely deliver the final service. Instead, they reveal which capabilities become useful first.

A single LEO satellite cannot provide continuous global positioning. That much is obvious. What is less obvious is how much useful information a single satellite can provide. At the most basic level, a single satellite can support timing-transfer experiments, receiver development, orbit and clock estimation validation, signal authentication concepts, and resilience demonstrations. More interestingly, the high dynamics of LEO satellites create large Doppler frequency that can become valuable navigation measurements. Long before a constellation can provide continuous and instantaneous positioning, it can contribute observability.

This observation is particularly important for opportunistic LEO PNT. The earliest post-Transit demonstrations with Orbcomm did not rely on dedicated navigation signals [1]. They relied on extracting useful navigation information from sparse, non-cooperative communications signals [2]. The positioning performance was limited, but the demonstrations established something far more important: navigation observables could exist even when navigation services did not (Figure 2).

That distinction continues to shape opportunistic LEO PNT today. A Starlink or OneWeb signal does not necessarily need to become a navigation service to create navigation value [3],[4]. If the signal provides useful Doppler, timing, carrier-phase, or ranging information, it can contribute to a navigation solution even when the constellation operator has made no formal commitment to navigation [5],[6]. In this sense, opportunistic systems may not be trying to become navigation infrastructure. They may instead become sources of observability that strengthen broader PNT architectures.

As additional satellites are added, the value increases considerably. Not necessarily because the system suddenly becomes a GPS replacement, but because it becomes a powerful augmenter. Several emerging architectures suggest that even modest LEO deployments can improve positioning performance when combined with GNSS. Benefits may include faster PPP convergence, improved velocity estimation, enhanced measurement diversity, increased resilience to GNSS disruptions, and improved performance in challenging urban environments where traditional satellite geometries are degraded.

This point is worth emphasizing. Many discussions implicitly assume LEO PNT must eventually replace GNSS to justify its existence. Yet, some of the strongest value propositions emerge when LEO and GNSS work together. The bar for becoming useful is much lower than the bar for becoming a global standalone navigation system.

In fact, timing users may become significant beneficiaries before positioning users. A positioning solution generally requires multiple observations. Timing applications often require less. For telecommunications networks, financial infrastructure, power grids, and data centers, the value proposition may not be a position solution at all. It may be access to an additional timing reference capable of constraining oscillator drift, improving holdover performance, or providing an independent source of synchronization. This possibility receives less attention than positioning, but it could prove commercially important. Some users may be willing to adopt LEO-derived timing services long before continuous global positioning services become available. 

The implications differ across the four schools of thought. For dedicated systems, early satellites provide opportunities to validate signals, timing architectures, user equipment, and operational concepts. For dual-purposed systems, they demonstrate how navigation can leverage existing communications infrastructure. For augmented architectures, even limited deployments may improve GNSS performance and resilience. For opportunistic systems, the first satellites are often enough to demonstrate the central premise that useful navigation information can be extracted from signals that were never designed for navigation in the first place.

The broader lesson is that constellations should not be judged exclusively on their ability to provide continuous positioning. They should also be judged on the value they create before continuous positioning becomes possible. A navigation service may require hundreds of satellites. A useful capability often requires far fewer.

QUESTION 3: What Must Happen Before Users Trust LEO PNT?

This is arguably the most difficult question facing the LEO PNT industry.

The navigation community often speaks about accuracy. Many users, especially in safety-critical systems, care just as much about trust.

A navigation solution can be extraordinarily accurate and still be unsuitable for operational use if users do not understand when it is wrong. In fact, one of the defining characteristics of navigation infrastructure is not that it always performs well. It is that users understand how well it is performing, when it is degraded, and when it should not be trusted.

Trust begins with signals. But it does not end there. Much of the public discussion surrounding LEO PNT focuses on waveforms, frequencies, signal power, and receiver sensitivity. These are important topics. Yet, navigation systems are not built on signals alone. Every satellite navigation solution depends fundamentally on three things: signal, satellite orbit and satellite clock.

Signals create measurements. Orbit and clock knowledge create meaning. A receiver must know where the satellite was when a signal was transmitted. A receiver must know what time the satellite thought it was. Without both, ranging becomes geometry without a reference.

This reality is particularly important in LEO. Unlike GNSS satellites residing in medium Earth orbit (MEO), LEO satellites experience significant atmospheric drag, more dynamic orbital environments, and rapidly evolving states. Orbital maneuvers will get more frequent and severe as LEO becomes more congested. Orbit determination is, therefore, not merely a technical detail. It is a foundational requirement for navigation performance.

The same is true for timing. Traditional GNSS achieves remarkable timing performance through sophisticated atomic clocks supported by extensive control infrastructures developed over decades. Most emerging LEO providers are pursuing different approaches. Some rely heavily on GNSS-derived synchronization. Others emphasize ground synchronization networks, optical inter-satellite links, distributed timing architectures, miniaturized atomic clocks, or combinations thereof. Each approach represents a different answer to a fundamental question: How does a LEO constellation know what time it is? That question may ultimately prove as important as signal design itself. 

Yet, even orbit and clock knowledge are only part of the trust equation. Evolving a demonstration to a service hinges on monitoring. A demonstration shows that a navigation solution can be produced. A service continuously evaluates whether that solution should be trusted. This distinction is often overlooked. Users frequently focus on positioning performance while paying less attention to monitoring infrastructure, anomaly detection, fault isolation, and quality assurance. Operational systems cannot afford such a luxury. The question is not whether a system works on a good day. The question is whether the system knows when it is having a bad day.

This is where integrity enters the discussion. Integrity is one of the most frequently used but least appreciated concepts in navigation. At its core, integrity addresses a simple question: Can the system detect and communicate when it should not be trusted?

For many applications, this question matters more than another meter of positioning accuracy. A highly accurate solution whose failures are invisible may be less valuable than a less accurate solution whose limitations are clearly understood. Integrity becomes particularly important as LEO PNT moves beyond demonstrations and into operational applications. Autonomous systems, critical infrastructure operators, timing users, aviation stakeholders, and defense users all require more than position estimates. They require confidence estimates. They need to know not only where they are, but how much they should trust where they are.

Closely related is continuity. Continuity turns a technical capability into infrastructure. A navigation demonstration may succeed one day, one week, or one month at a time. Infrastructure must succeed continuously. Satellites must be monitored. Clocks must remain synchronized. Orbit products must remain accurate. Service disruptions must be detected and managed.

This is one reason the path from demonstration to utility is often much longer than the path from concept to demonstration. The transition is not simply about launching more satellites. It is about institutionalizing trust (Figure 3).

When evaluating emerging LEO PNT systems, we should ask questions that receive far less attention than launch announcements:

• How are satellite orbits determined?

• How are clocks synchronized?

• How is integrity quantified?

• How are anomalies detected?

• How quickly are users alerted?

• What continuity targets are being met?

• What performance commitments are being made?

These questions may seem mundane compared with new signals, new satellite, and new constellation announcements. In reality, they are far more important. History suggests that navigation systems succeed not because they occasionally perform well, but because users know when they can trust them. Or, perhaps more importantly, when they cannot.

From Possibility to Infrastructure

The first era of LEO PNT asked whether navigation from LEO was possible. The second era asked whether useful observables could be extracted from dedicated and non-dedicated signals. The third era, the one we’re entering now, is asking something much harder: Can LEO PNT become trusted infrastructure?

That question extends far beyond satellites. It encompasses trust, integrity, timing, monitoring, economics, standards, governance, receiver ecosystems, and business continuity. Dedicated systems must prove they can scale. Dual-purpose systems must prove they can prioritize navigation when needed. Augmented systems must prove they add measurable value. Opportunistic systems must prove they can deliver robust performance despite relying on infrastructures they do not control.

The most interesting question in LEO PNT is therefore no longer: Can it work? The most interesting question is becoming: What must happen before users trust it?

The answer to that question will determine whether LEO PNT becomes a niche technology, a valuable augmentation layer, or one of the foundational pillars of the next generation PNT ecosystem. 

References

(1) J. Khalife and Z. Kassas, “Receiver design for Doppler positioning with LEO satellites,” IEEE International Conference on Acoustics, Speech, and Signal Processing, May 12-17, 2019, Brighton, UK, pp. 5506-5510.

(2) J. Khalife, M. Neinavaie, and Z. Kassas, “Navigation with differential carrier phase measurements from megaconstellation LEO satellites,” IEEE/ION Position, Location, and Navigation Symposium, Apr. 22-24, 2020, pp. 1393-1404

(3) Z. Kassas, M. Neinavaie, J. Khalife, N. Khairallah, S. Kozhaya, J. Haidar-Ahmad, and Z. Shadram, Enter LEO on the GNSS stage: navigation with Starlink satellites, Inside GNSS Magazine, Vol. 16, Issue 6, Dec. 2021, pp. 42-51.

(4) Z. Kassas, S. Kozhaya, J. Saroufim, H. Kanj, and S. Hayek, “A look at the stars: navigation with multi-constellation LEO satellite signals of opportunity,” Inside GNSS Magazine, Vol. 18, Issue 4, Aug. 2023, pp. 38-47.

(5) S. Kozhaya, J. Saroufim, and Z. Kassas, “Unveiling Starlink for PNT,” NAVIGATION, Journal of the Institute of Navigation, 2025, Vol. 72, no. 1, pp. 1-35.

(6) S. Kozhaya and Z. Kassas, “A first look at the OneWeb LEO constellation: beacons, beams, and positioning,” IEEE Transactions on Aerospace and Electronic Systems, 2024, Vol. 60, no. 5, pp. 7528-7534.

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Loran technology was a critical part of Allied transportation and logistics during WWII with over 70,000 receivers built for ships, aircraft, and submarines. According to the Smithsonian, by the height of the Cold War Loran coverage had extended to 70% of the northern hemisphere.

Although systems were disestablished in much of the west after the advent of GPS and in anticipation of Galileo, Loran systems have continued to provide high power, low frequency positioning, navigation and timing (PNT) services to vast areas in the east and billions of people in China, the Republic of Korea, Saudi Arabia, and Russia.

Today the modernized and more precise version, eLoran, is making a resurgence in the west as a way to greatly reduce the impacts of attacks on GNSS and demotivate those who might make attacks. It will also protect users and economies when space-based PNT is not available for whatever reason. 

This western renaissance is being led by the United Kingdom where loss of GPS due to severe space weather was first listed on its National Risk Register in 2012. The nation is establishing both a sovereign eLoran network and a fiber timing network that includes three timing centers to substantially mitigate that risk.

The UK has also committed to establishing four additional transmission sites to add to an eLoran timing signal that has been on-air for decades. Funding has been allocated, a search for the best locations and engagement with potential system providers and operators has begun.

France has committed to joining the U.K. with this effort, though whether they plan to create a sovereign system or merely build upon and broaden the reach of the U.K. network has yet to be announced. 

Maritime Use 

“As an island nation, we are much more reliant on maritime than others,” observed a British expert recently. “So, we are very concerned with the entire global maritime supply chain.” 

An information paper the U.K submitted to a recent International Maritime Organization (IMO) meeting describes in some detail the nation’s plan for and commitment to implement an eLoran network. Along with providing other details it says:

“The system is currently funded to reach full positioning and navigation services in England, Wales, the English Channel, Strait of Dover and Southern approaches to the United Kingdom by 2030, with full coverage to the North Sea, Ireland and Scotland from 2032. These dates are likely to accelerate due to formal partnerships with the Government of France and developing collaboration with other European partners, with formal announcements likely in autumn 2026.” 

Expanding beyond Europe, the paper also observes that eLoran systems are already serving areas in “… the Middle East, Northwest Europe and East Asia” and that it can help properly equipped vessels in those areas guard against GNSS disruption.

Some experts have observed that ships in the Strait of Hormuz could greatly benefit by accessing the network operated by the Kingdom of Saudi Arabia. The U.K. paper at IMO obliquely references this by discussing reducing “… the ability of ‘bad actors’ to disrupt strategically important flows…” and “…greater protection at those maritime chokepoints where precise navigation is most required.”

The paper also includes an invitation to other nations that operate or are interested in developing their own sovereign eLoran systems to contact the U.K. team. An industry rep subsequently reported interest from nations from nearly every region and continent. 

Recent severe GNSS jamming and spoofing events in key maritime areas, especially key choke points like the Strait of Hormuz, and to a lesser extent Bab al-Mandeb, have highlighted the need for PNT alternatives. Some maritime experts are evaluating near term eLoran solutions for these two locations as both may have sufficient service from the Kingdom of Saudi Arabia’s eLoran network for it to be a near term navigation alternative.

Aviation Applications

While often considered a maritime system, Loran has a long history of use in aviation as well. 

It was first used by military aircraft in WWII, an application that continued in the West until the late 1990s. As one example, the F-4E Phantom (top speed Mach 2.2) was equipped with a tactical Loran navigation system as part of the AN/ARN-101. Loran-C navigation was used extensively by both US military aviation and tanks during the first Gulf War (1990 – 91) because of the shortage of receivers for the new GPS system. 

The US Federal Aviation Administration (FAA) published the first Loran-related Technical Service Order (TSO-C60 for Airborne Loran-A Receiving Equipment) in May of 1959. Loran-A was the predecessor system that operated between 1800 and 2000 kHz. After Loran-C was selected as the designated radio navigation system for the Coastal Confluence Zone in 1974 and with the introduction of microprocessor technology, user equipment costs rapidly declined. By the mid-80’s there were nearly two dozen companies building user equipment for the aviation market. 

One of those companies was Texas Instruments (TI), introducing the first commercially available Loran-C aviation receiver in 1980. The following year the FAA issued TSO-C60a for airborne area navigation (RNAV) equipment using Loran inputs. By 1983, TI held Supplemental Type Certificates for installation on nearly every model of general aviation aircraft and helicopters used by commercial, military and private pilots.

Its use in civil aviation was sufficiently popular and robust that the FAA funded construction of additional Loran-C transmission sites in the middle of the U.S. to enable coast-to-coast service in the continental US. This, and Canada’s extensive network, enabled seamless Loran-C navigation from northern Mexico to southern Canada. To verify signal integrity to support non-precision approach procedures, a network of 196 monitors were installed at airports across the United States, including in Alaska.

The rapid and sustained rise of GNSS interference in so many parts of the world, along with existing and planned eLoran networks, has renewed interest in how the technology might benefit aviation. As examples:

• A 2018 IEEE paper lead by EUROCONTROL examined DME improvements, LDACS (L-band Digital Aeronautical Communication System), and eLoran. Of the three, eLoran is the only system that is beyond line of sight.
• In 2024 a Zurich University of Applied Sciences paper “Complementing GNSS for Resilient Performance Based Navigation” recommended authorities pursue “… eDME, eLORAN and LDACS-NAV, which have the commonality that they have excellent navigation performance at a lower expected lead time into the cockpit than other systems.”
• In June of this year “Bridging the North Atlantic: The Value of eLoran for Oceanic Airspace” was published by Zurich University of Applied Sciences. In it the author says that establishing three eLoran transmission sites in addition to those already planned by Britain could provide full coverage to the planet’s busiest oceanic air corridor.

Integration and certification requirements mean very long lead times for any new systems to be adopted in commercial aviation. Yet these papers and others have caught the attention of the Communications, Navigation and Surveillance Focus Group at the International Air Transport Association. This could possibly signal the earliest stages of that very long process.

Use by military aircraft and in general aviation as a non-integrated supplemental navigation capability is more likely in the near term. 

Multi-modal Transportation

While maritime and aviation are the highest priority modes, wide area RF-based navigation systems can often serve all forms of transportation. The international eLoran Standards Working Group demonstrated its use in a drone recently. Others have been experimenting with use in surface transportation.

Deployable eLoran 

The U.K. has also contracted for development of a deployable, tactical eLoran capability. Ministry of Defence officials have dubbed the project “Urgent Compass” and tout the technology’s exceptional resilience to interference as being crucial on the battlefield. The new system is expected to build upon the deployable “Loran-D” developed by the U.S. Air Force in 1964 and used throughout the 1960’s and 70’s. The Department of Defense re-examined the technology in the early 2000’s. Last year Germany’s armed forces also fielded and tested a tactical eLoran system.

Standards and Coordination

Several efforts are underway to develop standards for eLoran beyond those already documented in the SAE 9990 series. 

An initial international standards working group that started with the UK, Republic of Korea, and France, now includes the European Space Agency’s (ESA) Navigation Innovation Support Program (NAVISP) Engineering Team. This group convened in Seoul this July to continue its efforts. Group leaders say they want to grow it to include representatives from all interested nations.  

The International Organization for Marine Aids to Navigation (IALA) is has also been involved in this working group from the beginning. Recently the IALA council has formally agreed to take on responsibility for international coordination of eLoran operations. 

IEEE has also taken an interest. A session on eLoran and R-mode will be featured at its December navigation conference in Munich. Papers from the UK General Lighthouse Authority, Roke, Cambridge, Georgia Tech, and others have been submitted.

Complementing Space

ESA’s NAVISP has long been involved with the technology. While it is definitely not a space system, eLoran can complement and reinforce space signals. The availability of widely available terrestrial PNT systems can also make attacks on GNSS signals less likely by reducing their impact and demotivating bad actors. 

In one project NAVISP funded Roke’s development of an eLoran antenna for handheld devices in 2024. Going forward the organization intends to remain involved. For example, this October NAVISP’s Industry Days in Rome will feature a panel of experts on GNSS-independent systems that will include eLoran.

Looking Ahead

Whether eLoran coverage continues to extend to what it once was or beyond is yet to be seen. Its broad area coverage and signal characteristics so radically different from space-based systems seem for many to make it an ideal complement for GNSS. 

Yet the success of PNT signals from low earth orbit, magnetic systems, quantum sensors and the like, will undoubtedly be factors. 

What seems certain is that interference with GNSS systems and signals will continue to increase. Sovereign systems like eLoran that can serve an infinite number of users over continental size areas will continue to be of great interest. Indications are that eLoran is rapidly moving from a legacy technology to becoming a strategic component of resilient PNT.

The post eLoran Surging as Protection for GNSS and Users  appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

The Federal Communications Commission (FCC) has authorized Xona to broadcast the world’s first commercial navigation signal designed to operate alongside GPS from its full Low Earth Orbit satellite constellation.

The first-of-its-kind authorization comes as Xona prepares to launch its first six production satellites in October and scales manufacturing at its satellite production facility in Burlingame, California. With this authorization, Xona will become the only FFC-authorized private navigation constellation to operate next to nation-state systems from the United States, Europe, China, and Russia.

Pulsar is the first navigation system purpose-built for the demands of modern devices and infrastructure. Its signals are up to 100 times stronger than GPS, protected against spoofing through a dynamic cryptographic watermark, and designed to work with existing navigation hardware through software and firmware updates.

The new authorization expands upon the FCC license granted for Pulsar-0, Xona’s final demonstration mission and the first commercial satellite authorized to broadcast radionavigation signals in L-band spectrum alongside GPS. The new authorization expands this authorization to Xona’s planned full constellation as the company scales production at its Burlingame production facility.

“From the beginning, we were told that what we wanted to do was impossible,” said Brian Manning, Co-Founder and CEO of Xona. “A commercial company had never built a system like Pulsar, and no one had been authorized to introduce a new, high-power navigation signal alongside GPS. This decision is the culmination of years of engineering, testing and coordination, clearing the way for a capability the world increasingly needs.”

Operating alongside GPS required Xona to demonstrate that Pulsar could deliver a substantially stronger signal without interfering with the navigation and aviation services already operating in the spectrum band. The company worked extensively with the FCC, U.S. government agencies, aviation stakeholders and international governments to evaluate Pulsar’s signal performance and coordinate its operation.

Rather than avoiding those constraints by building in less established frequency bands for navigation, Xona chose the harder path: engineering Pulsar for the L-band spectrum already used by more than six billion Global Navigation Satellite System (GNSS)-enabled devices worldwide. By broadcasting a new proprietary signal adjacent to GPS, Pulsar has demonstrated it can integrate into many existing receivers without requiring an entirely new hardware ecosystem.

“Making room for something new required us to demonstrate that we understood the importance of what was already there,” said Christina Youn, General Counsel and Vice President of External Affairs at Xona. “GPS supports aviation, communications, emergency response, financial markets and countless systems people rely on every day. We did not ask regulators or the industry to take our claims on faith. We designed for coexistence, subjected that design to rigorous scrutiny, and then proved it through live transmissions from orbit.”

Since launching in June 2025, Pulsar-0 has completed more than 350 transmission passes across four continents. Its live signals have been independently tracked by more than a dozen commercial receivers, demonstrated compatibility with existing GNSS on existing navigation hardware worldwide, and supported continued testing of Xona’s signal performance in real-world environments.

The post U.S. Clears Xona’s Pulsar for Full Constellation Deployment appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

NATHANIEL THOMAS, TIM MURPHY, CHRISTOPHER NGUYEN, COLIN WILKINS, BOEING

Over the last few years, GNSS Radio Frequency Interference (RFI) has become a major disruptor to commercial air travel. GNSS RFI affects not only air transportation but also maritime navigation, emergency services, and other industry functions. Within commercial air travel, flight routing, operator maintenance burden, and pilot workload are areas commonly impacted by exposure to GNSS RFI.

Boeing has continually worked with operators, regulators and suppliers to establish a coherent strategy to address the impacts of GNSS RFI on Boeing aircraft. Through its phased approach, Boeing has established a monitoring system and associated analysis pipeline for the in-service fleet’s exposure to GNSS RFI events. The monitoring is conducted by the GPS Event Monitor (GEM) report that operates within the maintenance function of the airplane and logs details about which RFI symptoms a plane experienced and where in the world it was when the symptoms occurred. This data is provided back to Boeing, and datasets are created to compare typical symptom occurrences in a defined geographic region or for a specific GNSS receiver type. Boeing continually updates these analytics to keep key stakeholders informed of global interference trends as they continue to evolve.

Boeing’s Strategy

Global involvement from regulators, industries and original equipment manufacturers are needed to achieve GNSS RFI resiliency. Boeing Commercial Airplanes’ comprehensive strategy to identify and mitigate issues related to GNSS RFI is illustrated in Figure 1. The strategy is organized into three major phases: Containment, Improvement and Resilience. Figure 1 may imply these phases are sequential, however, they should more accurately be understood as work streams that happen in parallel. Boeing is working on all three phases at once, however, results from each phase feeds the work of subsequent phases.

Here’s what each phase entails: 

Containment: The containment phase focuses on fully understanding the impacts of RFI and doing whatever can be done expeditiously to help Boeing customers deal with GNSS RFI.

Boeing has worked closely with operators to collect data related to GNSS RFI and to share information and recommendations for flight and maintenance crews in a variety of forums. A crucial piece of this collaboration is the release of Flight Operations Technical Bulletins (FOTBs) for the various Boeing models. These FOTBs detail the expected flight deck effects and recommended crew mitigations for GPS and GPS user systems across various Boeing aircraft models.

Initially, Boeing analyzed reports of operator experiences to understand the kinds of RFI events seen in the field. Early on, it was determined manual reporting of RFI events would not be efficient or effective because of the overwhelming occurrence rate of GNSS RFI and potential data inconsistencies. So, Boeing developed and released software that automatically gathers data on adverse GPS events and creates the automated GEM reports, which come from the Aircraft Condition Monitoring System (ACMS) or Aircraft Condition Monitoring Function (ACMF), depending on airplane models. 

These reports are generated via user-modifiable software inside the aircraft maintenance systems. The software algorithms include robust logic for detecting adverse GPS events and informing operators via datalink messages sent directly to the airlines. These datalink messages are also routed to Boeing, where they are accumulated into a database for further analysis. The GEM report data can also (at the discretion of the operator) be sent/uplinked to the flight deck (as a COMM message) to provide the aircrew situational awareness (Figures 4 and 5). GEM data generation and display requires existing airborne and ground equipment, referred to as the GEM System in Figures 2 and 3.

Boeing uses this data to understand trends, identify zones of high interference activity, and analyze avionics system performance. This information is shared regularly with operators. The data from GEM helps Boeing identify which types of events should be a priority to address in the Improvement and Resilience phases. The data can be monitored over time to verify predicted performance improvements.

Improvement: In this phase, Boeing identifies, specifies, implements and fields actual changes to airplane equipment to mitigate the operational impacts of GNSS RFI. Using reports and data provided by its operators, in conjunction with GEM data, Boeing conducts root cause investigations to identify possible engineering changes that will improve airplane system resilience. For example, Boeing is working on certifying new multi-mode receiver (MMR) software updates on its airplanes to make them more resilient to spoofing. These enhancements to MMR resilience against GNSS RFI will prevent erroneous GNSS data from impacting downstream GNSS user systems, enhancing performance. Additionally, Boeing has completed root cause investigations for Enhanced Ground Proximity Warning Systems (EGPWS) issues due to GNSS RFI with the system supplier and is working on certifying new changes on the EGPWS parts to be made available to Boeing operators to retrofit their fleets.

Throughout the Improvement phase, the GEM system validates that the changes implemented are delivering the expected improvement in performance in the presence of GNSS RFI.

Resilience: New functionality is added to airplanes in this phase that makes them more resilient to GNSS RFI. Boeing is conducting a comprehensive review of its design requirements and philosophy for systems that use GPS in light of the current challenges associated with GNSS RFI. Boeing continues to invest in interference-resistant avionics solutions, including next-generation dual-frequency multi-constellation MMRs that may incorporate signal authentication capability and Controlled Reception Pattern Antennas (CRPAs). 

The schedule and availability of these solutions is paced by standards development. When standards are mature, Boeing intends to engage with suppliers, operators and industry experts to develop these new solutions for GNSS RFI. In addition, Boeing is studying Alternative or Complementary PNT systems that might be deployed to make navigation capabilities more resilient at the airplane level. The ultimate goal of the resilience phase is to make GNSS RFI a non-issue with respect to normal airline operations.

The GEM System

The GEM System illustrated in Figure 2 is representative of 777, 787 and 777X.

The GEM system consists of onboard ACMF and a Communication function and ground system to move and display GEM data. Starting at ACMF detection of disagreement or abnormality in the GPS data, ACMF reports the event via ACARS downlink. On the ground, the Airline Operation Center or Boeing Airplane Health Management (AHM) services receives the GEM report, then decodes and stores the data for analysis. They also automate the uplink messaging with GEM data to notify aircrews. Back on board, the Flight Deck Communication Function (FDCF) or Communication Management Function (CMF) receives the GEM data uplink message, decodes it and displays it to aircrews. The aircrews can view the GEM data and request a manual update of fresh GEM data on-demand instead of waiting for the next event.

GEM report logic in ACMF is designed to automatically detect GPS position and satellite data that is inconsistent between multiple GPS sources or inconsistent with inertial and air data. The monitor logic is also designed to detect GPS date and time shifts after the start of the flight based on the reference date and time snapshot at the beginning of the flight and independently count forward. The report is generated with the GPS DATA DISAGREE flag set to YES if any of the known symptoms below are detected:

• DATE SHIFT. The date components of the GPS receiver timestamp are compared to uncorrupted reference values to determine if deviation criteria are met to trigger a date shift.

• TIME SHIFT. The time components of the GPS receiver timestamp are compared to uncorrupted reference values to determine if deviation criteria are met to trigger a time shift.

• POSITION SHIFT OR INVALID. The latitude and longitude from a GPS receiver are compared to the uncorrupted inertial position data to determine if deviation criteria are met to trigger a position shift.

• ALTITUDE SHIFT OR INVALID. The altitude from a GPS receiver is compared to the uncorrupted barometric altitude data to determine if deviation criteria are met to trigger an altitude shift.

• VFOM LARGE OR INVALID. The behavior of the Vertical Figure of Merit from a GPS receiver is analyzed to determine if it becomes too large or unstable, in which case this event flag is set.

• SATELLITES TRACKED LOW. The number of satellites tracked from a GPS receiver is analyzed to determine if enough satellites are present to compute a navigation solution, if not this event flag is set.

• NOT IN NAV MODE. The operational mode from a GPS receiver is analyzed to determine if the receiver is operating in one of several navigation modes or another mode. If the operational mode is not one of the navigation modes, this event flag is set.

The GEM System illustrated in Figure 3 is representative of the 737 MAX. GEM data is displayed in real-time with GPS DATA DISAGREE flags on the Multi-functional Control Display Unit (MCDU) under the ACMS sub-menu, and reports are downlinked. Ground operations can relay the message to notify aircrew of the event. That message is also displayed on MCDU under the datalink sub-menu. Because all data ends up on the MCDU, the uplink notification message can simply state the event: GPS RFI ENTRY/CONTINUE/RECOVERY. If aircrews need to view the detailed data, they can access GEM data from the ACMS sub-menu. Note aircrews do not need to send a request to refresh GEM data because the data is updating in real-time.

GEM Reporting Frequency

Once an event is detected (the first among all other events), a report is generated. This first report is known as the GPS RFI Entry report, indicating the airplane is experiencing a possible RFI related event. In this case, the GPS DATA DISAGREE flag is set to YES.

If one or more events are active after the Entry report, the periodic report is generated every 20 minutes for the first hour and then followed by a report every one hour after the first hour. These reports are known as GPS RFI Continue reports. In this case, the GPS DATA DISAGREE flag remains set to YES.

Once all events are recovered (all events are no longer active for 20 minutes), the GPS RFI Recovery report is generated to indicate GPS data are back to normal and the aircraft has possibly exited the RFI region. In this case, the GPS DATA DISAGREE flag is reset to NO to reflect recovery from all symptoms.

Note: All timers might be customized or programmed to be modifiable parameters based on airline needs.

GEM Display to Aircrews

Optionally, flight operations at the airlines can decide if they want to receive the GEM report data update in the communication function of the airplane. If airlines choose to do this, an ACARS or AHM engineer will script the capability to automatically detect the GEM report downlink and relay the data to aircrews via an ACARS uplink message.

Once the communication function receives the message, aircrews will receive a notification via a COMM reminder on the forward display and an aural cue in the cockpit. GEM report data uplink produces two pages of information for the aircrews. The first page provides the top level GPS DATA DISAGREE flag, the seven associated symptom flags, and when the report was generated. The page also has the following control actions for pilots:

The REQUEST UPDATE, when commanded by the SEND action, will downlink the request to ground. Ground operation relays the request by doing an uplink to request ACMF to generate a report on demand. Once ACMF generates the new report, the data path repeats itself as described in the GEM System in Figure 2.

The DISABLE UPDATE, when commanded by the SEND action, will tell ground operation to stop the automatic relay of GEM data uplink until the end of the flight or until aircrews enable the feature again.

A typical GEM data display to aircrews is illustrated in Figure 4. This example is from the 787 model, and shows the TIME SHIFT symptom has occurred on both GPS receivers.

The second page of a GEM report, illustrated in Figure 4, provides situational awareness in the form of raw data from GPS used to generate the GPS event YES/NO indications, as well as additional information. Each of the items on the second page are described here:

GPS DATA DISAGREE. This is the same indicator as Page 1.

• ALT (ft) The BARO, GPS-L and GPS-R altitudes are shown for reference. The barometric altitude is sourced from air data and is expected to differ from GPS altitudes within a specified tolerance.

SATELLITES. The VIEW column indicates the number of satellites that should be in view. Large differences could be an indication of spoofing impacting one GPS receiver and not the other. A zero in this location could indicate a reset and acquisition mode are in progress for that receiver.

• The TRACKED column indicates the number of satellites acquired and tracked by the corresponding GPS receiver. The numbers can vary from one receiver to the other, although large differences could indicate interference on one receiver and different impacts on the other receiver. Zero tracked satellites indicates jamming or a receiver in acquisition mode attempting to regain navigation mode.

• The MODE column indicates the navigation mode of the receiver. Mode 3 is a navigation mode. All other modes are alternate or non-normal modes that should not occur during flight.

• The ANT FAIL indicator is set to Y for YES when the corresponding GPS receiver is not operational due to a detected antenna failure. This antenna fail indication can help distinguish an antenna fault from interference.

• VFOM is for situational awareness and can help aid in understanding Page 1 information.

• HIL indicates the Horizontal Integrity Limit (HIL) and is for situational awareness. This parameter is needed for RNP/RNAV and ADS-B Out.

TIMESTAMPS. These timestamps are provided for awareness:

• On most airplane models, the time is based on GPS when valid, but may coast after loss of GPS. Airplane time can be erroneous if GPS time is erroneous.

• GPS L or R time is invalid during interference or potentially erroneous during spoofing, although some receivers may invalidate GPS outputs during spoofing. Due to system display limitations, invalid GPS date and time always displays as “11-NOV-2011 11:11:11.”

• GROUND time is sent from the ground in the COMM message. This time is independent from airplane or GPS time and is used as a comparison against airplane and GPS times.

The ACMS GEM data on the 737 MAX shows similar content as described but are formatted to fit MCDU limit screen size (Figure 5).

GEM Report Use by Airlines and Boeing

The GEM report has been deployed on the 777 aircraft since June 2024, on the 787 aircraft since April 2025, and on the 737 MAX aircraft since April 2026. Service letters are published with a suggested monitoring algorithm that would allow operators of legacy models like the 737(NG and Classic), 747, 757 and 767 to develop and install a version of the GEM report on those models. During the time period of data collection, Boeing has received over 1.3 million GEM reports from over 1,000 unique aircraft in service across 52 different global operators.

Insights from GEM Data Analytics

The information provided by the GEM reports serves as an enabler for useful analytics related to GNSS RFI. First, the symptom flags and airplane inertial position, coupled with the time history of reports for a given flight leg, allow Boeing to determine where an airplane was located when a GPS RFI symptom first occurred. This information, when combined with full flight position history from sources such as ADS-B data, allows Boeing to create Flight Information Region (FIR) heat maps based on the occurrence rate of specific GPS RFI symptoms or symptom classes.

For the purposes of analysis, the seven GEM data symptom types are placed into three main symptom classes: GPS Loss, Position Error and Date/Time Error. All symptom classes indicate a set of behaviors observed by the GEM report at the GPS receiver level.

GPS Loss indicates the presence of jamming symptoms in the GNSS receiver(s) as indicated by:

• Satellites Tracked Low Symptom Flags

• Receiver Not in Navigation Mode Symptom Flags

Position Error indicates the presence of spoofing symptoms with GNSS receiver(s) horizontal and vertical position solutions as indicated by:

• Lateral Position Shift or Invalid Lateral Position Symptom Flags

• Altitude Shift or Invalid Altitude Symptom Flags

• VFOM Large or Invalid Symptom Flags

Date/Time Error. The presence of spoofing symptoms with GNSS receiver(s) date and time solutions as indicated by:

• Date Shift or Invalid Date Symptom Flags

• Time Shift or Invalid Time Symptom Flags

These symptom classes are not mutually exclusive; many flights experience symptoms from all three symptom classes. Figure 6 provides details regarding symptom class coincidence and associated recovery trends on flight legs flown by 777 and 787 aircraft equipped with the GEM report between August 1, 2025, and January 31, 2026. 

Figure 6 provides a visual breakdown of symptom class coincidence and the associated recovery outcomes. A few observations can be made based on this visual. First, the GPS Loss symptom class is the most common symptom class present across all combinations, followed by Position Error and then Date/Time Error. Second, Date/Time Error symptoms most commonly occur when a flight leg also experiences Position Error and/or GPS Loss symptoms. Finally, the recovery outcome of a flight leg can vary drastically based on the combination of symptom classes that a flight leg experiences.

During the period of data collection, approximately 31% of flights experienced GPS Loss, Position Error and Date/Time Error symptoms. Only 37% of the flight legs that experienced symptoms from all three classes landed with both GPS receivers fully recovered. The second most common outcome is a flight leg only experiencing symptoms from the GPS Loss class. This group represents approximately 28% of symptomatic flights, with nearly 81% of flight legs experiencing this symptom combination indicating both receivers fully recover before landing. The substantial difference in recovery outcomes highlights the influence of the symptom class combination experienced by a flight leg on recovery outcomes.

Within the GEM dataset, Boeing tracks the initialization of a symptom on a flight leg as well as any reoccurrence after a symptom’s recovery criteria are met. Both the initializations and reoccurrence contribute to the numerator of the occurrence rate calculation within a given FIR. The denominator in the occurrence rate calculation is determined by the total number of flights equipped with the GEM report that flew through the FIR in the period of interest. 

Figure 7 shows the global FIR heat map for all GEM symptom occurrences. To create this map, a global OR logical operation is used in the FIR occurrence rate calculation, meaning if a flight leg has either an initialization or reoccurrence of any GEM report symptom in the FIR, it will contribute to the overall occurrence rate of interference symptoms within the FIR. 

The January 2026 data shown in Figure 7 shows substantial interference activity in Russia, Eastern Europe, the Middle East region, the Eastern Africa region, the Black Sea region, the 
region surrounding Venezuela, and the Southeast Asia region.

In addition to the All Symptom type heat map, Boeing also produces heat maps and regional datasets to compare individual symptom occurrence rates. An example of this is shown for the low satellite track count symptom in Figure 8. 
For the individual symptom maps, in addition to color coding FIRs by their symptom occurrence rate, the inertial positions of the aircraft at the time of symptom initialization (black dots) or reoccurrences (blue dots) are also mapped. The inertial position is from an uncorrupted inertial solution that is independent of GNSS information. This provides important contextual information as some FIRs are large and interference may only impact a portion of the airspace. The initialization and reoccurrence information provide a good visualization of where interference has historically occurred within a given FIR.

Another example of a symptom specific heat map is given in Figure 9. This figure shows the initialization and reoccurrences of the Date Shift symptom. Date shifts are believed to only occur as a result of specific types of spoofing attacks. Therefore, comparing Figures 8 and 9 can give some insight into the relative frequency of jamming that results in a denial of service and spoofing attacks that result in a Date Shift.

The ever-growing database of GEM reports can be analyzed in many ways, providing insights into what is really going on with Boeing airplanes in the field. Boeing can sort the data according to airplane model, airline, receiver manufacturer, and even filter by specific part numbers. This has proven to be a valuable tool as we continue to work with customers on root cause analyses when new types of GNSS RFI are experienced. 

Unfortunately, the threats to GNSS evolve over time and spoofing attacks appear to be getting more sophisticated. This analytical tool can help as we respond to changes in the threat landscape. Furthermore, we can add additional logic to GEM reporting to detect new symptoms as they are identified. Probably most valuable of all, we can compare the performance of specific receivers with different software uploads to verify software improvements are indeed effective at addressing the issues they were intended to mitigate.

Future GNSS receiver versions are expected to have richer jamming and spoofing detection reporting at the receiver level. When these are available, Boeing will incorporate that information in the triggering algorithms and GEM reports as appropriate.

Heat maps such as those shown in Figures 7, 8 and 9 are not uncommon. Many organizations have websites that provide similar heat maps (see example at gpsjam.org). These can be very useful tools to see general trends in GNSS RFI. However, they have limitations in that the GNSS RFI detection is usually done by inference based on ADS-B reporting. The GEM system collects actual events reported by airplanes and does not rely on inference of jamming and/or spoofing based on ADS-B observations. 

Other systems based on ADS-B reports may have some ability to sort data according to aircraft, but generally don’t have the visibility of receiver types or even receiver part numbers. The GEM data and associated maps also provide a greater level of symptom specificity than what is provided by ADS-B only data solutions.

Future Work

As both the global GNSS interference environment and GNSS receivers continue to evolve, Boeing will continue to evolve the GEM report system with the speed of relevance. As new symptoms or behaviors resulting from GNSS interference are identified, they will be added to future revisions of the GEM report. GEM report data will also continue to be leveraged to assess GNSS receiver performance as new technologies are deployed to the in-service fleet. This analysis will provide valuable feedback to ensure new solutions continue to exhibit the performance improvements in GNSS interference environments the design intended. 

Authors

Nathaniel Thomas is a Systems Engineer at the Boeing Company. During Boeing’s ongoing response to GNSS Interference, he has served as the primary focal for data analytics activities related to GNSS Interference. He holds a B.S. and M.S. in Aeronautical and Astronautical Engineering from Purdue University.

Tim Murphy is a Senior Technical Fellow with the Boeing Company where he works on communication, navigation, surveillance (CNS) and Spectrum issues related to Air Traffic Management. Tim has more than 43 years of experience in the field of radio CNS systems for civil aviation. The current focus of his work is avionics for new airplane product development, autonomy and next generation CNS technologies to support air traffic management. Tim is very active in the development of domestic and international standards for CNS technologies and Spectrum for use by commercial aviation.

Christopher Nguyen is a Lead Electronic Systems Design & Analysis Engineer at the Boeing Company. He leads the development, testing and release of Airline Modifiable Information (AMI) software, including reports used in the GPS Radio Frequency Interference response. He has 21 years of software development experience at Boeing Commercial and Boeing Defense businesses. He earned his B.S in Electrical and Computer Engineering from Cal Poly Pomona, M.Engr in Software Engineering and Management from the University of Illinois, Chicago.

Colin Wilkins is a functional manager in Boeing Avionics where he leads a team that designs and integrates Radio Navigation equipment, including GPS equipment, for all Boeing production models. He and his team lead the development of the GEM logic and how to use the analytics to inform future equipment and aircraft design.

The post Boeing’s Approach to Mitigating the Impacts of GNSS RFI appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

As global telecommunications networks, power grids, and data centers increasingly depend on ultra-precise timing, relying on a solitary GNSS reference exposes networks to risks like jamming, spoofing, and signal multipath. To build a resilient architecture, the Coherent Clock project introduced a distributed clock ensemble mechanism. Instead of treating receivers as isolated units, the system aggregates timing data from multiple geographically distributed GNSS nodes via fiber-optic networks to synthesize an optimized, secure global time solution.

The architecture utilizes Safran’s WR-Z16 LJ units, which combine embedded Septentrio Mosaic-T GNSS receivers with the IEEE 1588-2019 high accuracy precision time protocol, heavily based on White Rabbit (WR-PTP) technology. This mesh topology establishes a distributed network that removes any single grandmaster dependency, enabling seamless sub-nanosecond phase synchronization over metropolitan distances.

Rigorous testing and verification

Safran presented the final results of the project at a recent ESA-hosted event. Central to the platform is the distributed clock ensemble server (DiCES), which monitors node status and historical Kalman filter metrics through a dedicated representational state transfer application programming interface. DiCES computes real-time phase and frequency corrections, delivering them back to individual nodes to drive a local hardware ‘paper clock’ ensemble with sub-picosecond resolution.

The team executed verification campaigns using simulated rubidium clocks at Safran’s timing laboratory in Granada, Spain. They followed this with physical testing using multi-node configurations of real caesium and maser standards at the European Space Research and Technology Centre (ESTEC) UTC laboratory in Noordwijk, Netherlands.

Under benign baseline conditions, the synthesized ensemble demonstrated superior long-term stability compared to any single standalone reference clock. Crucially, when subjected to hostile test scenarios, including forced node power failure, 10-minute connector detachments, and emulated sub-nanosecond phase and frequency jumps, the Kalman-plus-weights algorithm instantly mitigated anomalies. The system isolated anomalous nodes by setting their algorithmic weight to zero without compromising aggregate network timing or output stability.

The successful demonstration concludes the project at technology readiness level 5. Looking forward, Safran plans to harden the technology, integrate absolute UTC-traceability testing, implement optimized steering, and deploy multi-site commercial pilots, to align fully with future 5G standards.

The post Safran Validates Resilient Sub-Nanosecond Coherent Clock appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

Passive, outdated approaches to PNT are endangering our nation.

GPS denial and manipulation are a growing threat, and have been for more than 25 years. A plot of interference incidents (Figure 1) shows terrestrial-based GPS disruptions spreading across the globe like a cancer. And on top of that, there isn’t a place on the planet that’s beyond the reach of recently discovered space-based disruption weapons.

Yet, America has no widely adopted backup service to deter interference and protect users. This is because the U.S. has been pursuing an unsuccessful,15-year-old strategy that has gone unchallenged through two Democratic and two Republican administrations.

It is past time for a change. Subject matter experts have been talking about the nation’s over-dependence on GPS for decades. It’s been:

• 26 years since the Clinton administration identified the problem.
• 22 years since President George W. Bush mandated a GPS backup.
• 18 years since the government announced a solution.
• 15 years since the Office of Management and Budget (OMB) persuaded the president to reject the interagency solution.
• 8 years since Congress passed and President Trump signed an act into law mandating a terrestrial timing system to backup GPS.
• 6 years since President Trump signed an executive order designed to “fix” the problem.

Yet, America’s over-dependence on GPS is greater than ever, with no alternatives that could “get the bullseye off GPS” in sight.

In the years since the first Trump administration addressed PNT, the risk to the U.S. from this vulnerability has increased dramatically. The signs include:

• Recent revelations that Russia has been periodically exercising a space-based weapon since 2019 that interferes with GPS across continental size areas. (They have been doing the same to China’s BeiDou since 2020).
• Russia’s 2021 threat to destroy all GPS satellites if NATO interfered with its invasion of Ukraine.
• The use of wide area jamming and spoofing by numerous nations in the Mediterranean, Middle East and Asia.
• China’s completion of an integrated and resilient PNT architecture that includes signals from space, eLoran and fiber ensuring it can withstand GNSS disruption. This gives it significant tactical and strategic advantages over the U.S. and the West.

Past Time for a New Approach

Trump administration PNT policies and approaches were established before these concerning dangers came to light. Equally concerning, these still in-force documents are based heavily on decades-old policies that, even then, many thought inadequate.

The first Trump administration addressed PNT in two documents:

• Executive Order 13905, “Strengthening National Resilience Through Responsible Use of Positioning, Navigation, and Timing Services,” February 12, 2020.
• Space Policy Directive (SPD) 7, “The United States Space-Based Positioning, Navigation, and Timing Policy,” January 15, 2021.

In both, the administration adopted its predecessors’ passive, laissez faire approach, leaving our critical national security interests to the whims of fate.

The provisions of the executive order were, as attorneys are fond of saying, “necessary but not sufficient.” The order only addressed critical infrastructure, focused on educating users and fell far short of taking or compelling any actions to make the nation safer.

In SPD 7, the Trump administration’s discussion of protecting GPS with a backup is almost a word-for word repeat of a document from 11 years before:

2010 National Space Policy:

“…identify and implement, as necessary and appropriate, redundant and back-up systems or approaches for critical infrastructure, key resources, and mission-essential functions.”

2021 Space Policy Directive 7:

“…identify and implement, as appropriate, alternative sources of PNT for critical infrastructure, key resources, and mission-essential functions.”

Contrasting sharply with the passive “maybe someday” approaches is the assertive and proactive direction in President George W. Bush’s 2004 mandate. With the attacks of 9/11 still fresh, he was determined to make America able to withstand any future assault, regardless of the vector.

According to the NSPD-39 Fact Sheet, Bush’s National Security Presidential Directive 39 “U.S. Space-Based Position, Navigation, and Timing Policy” in December 2004 required the U.S. Department of Transportation (DOT) to:

“In coordination with the Secretary of Homeland Security, develop, acquire, operate, and maintain backup position, navigation, and timing capabilities that can support critical transportation, homeland security, and other critical civil and commercial infrastructure applications within the United States, in the event of a disruption of the Global Positioning System or other space-based positioning, navigation, and timing services.”

A Flawed “Action Plan”

Officials in this Trump administration have not promulgated any new or updated PNT policy. Instead, they are operating with two government documents published just before they took office. These are:

• Department of Transportation PNT Strategic Plan, December 2024.
• Complementary PNT Action Plan, DOT Actions to Drive CPNT Adoption, March 2024.

Both documents expand upon previous commitments to do things on the periphery of resilient PNT without actually ensuring any national capability is deployed.Yet, initially, the Complementary PNT Action Plan did seem to hold out a ray of hope officials have cited as a pathway to success: the promise of “government as first adopter.”

This is the idea that the federal government would lead the way in adopting complementary and alternate PNT services, setting an example for the nation by showing the government is serious about the need to use such systems. Also, by establishing long-term contracts, the market would be reassured such services would be around for the long haul and worth investing in.

Yet, two years after the action plan was published, there seems to have been very little to no government adoption.

Why? It’s undoubtedly because, as outlined in the plan, “government as first adopter” is fatally flawed in two ways.

First, it contemplates the DOT and other federal departments acquiring PNT services to support assets in the privately owned critical infrastructure sectors they supervise. While the DOT has the legal authority to do that, other departments do not. That puts everyone but DOT out of the picture.

It also doesn’t help that DOT attempts to acquire services to support transportation systems have been continually rebuffed by OMB. If the department responsible for leading civil PNT policy isn’t getting anywhere, it is difficult to imagine others without specific legal authority succeeding.

The second problem is funding. While the cost of alternative PNT services is expected to be minimal compared to the overall federal budget, it will cost something. And as big as the federal budget has grown, every penny is already spoken for.

Even positing other federal departments were (1) willing to act without legal authority, and (2) act on a plan promulgated by a technical center at another department with no authority to direct their actions, they would still have to find funds for something that was not their idea. Either new funds would have to be requested from Congress (which requires OMB approval), or other program would have to be decremented or sacrificed (again, requiring OMB approval). Both scenarios are exceptionally unlikely. Consequently, “government as first adopter” is not a conceivable action or a plan. Rather, it seems an empty promise designed to mislead the public and senior officials.

Breaking From the Ineffective Past

As Rita Mae Brown put it in her 1983 novel “Sudden Death,” “Insanity is doing the same thing over and over again but expecting different results.”

For more than two decades, the United States has been talking about GPS vulnerability and the need for complementary, alternative and backup capability. All that while diligent but unempowered government officials have been prevented from acting to make America safer.

Every U.S. national PNT policy and action after 2004 has been ineffectual when it comes to protecting GPS services with a complementary and backup capability.

Nations across the globe are establishing or already have resilient core national PNT architectures that have, at their center, GPS and other space-based PNT, but also include terrestrial broadcast PNT and fiber-based precise timing systems. These provide security for critical infrastructure, small and big companies, and individual citizens alike. They protect economies in the event of severe solar weather and ensure defense industries can keep producing even if space-based signals are denied. All while America is becoming one of the least protected and most vulnerable nations.

It is past time for the Trump administration to break from the failed past and take an active role in ensuring American PNT safety and security.

The post Dear Trump Administration: It’s Time for a New Approach to PNT appeared first on Inside GNSS - Global Navigation Satellite Systems Engineering, Policy, and Design.

FEI President and CEO Tom McClelland noted the order arrived roughly four months after the company’s initial lunar PNT contract, which FEI announced in March 2026 for $7 million, also for lunar PNT atomic clocks.

Part of a broader push into space PNT and alternative-PNT markets

McClelland framed the repeat order as evidence of FEI’s ability to scale space exploration business, and pointed to lunar PNT as one of several markets — alongside proliferated satellites, quantum sensing, space defense and alternative-PNT — that the company is targeting for growth built on its existing space and defense timing business.

The award follows a separate $18 million set of contracts FEI announced July 23, which included an $11 million award from an aerospace prime for a satellite frequency-generation system, plus roughly $7 million in follow-on production work for space oscillators and non-space government programs. It also follows FEI’s July 15 fourth-quarter and fiscal-year 2026 results, in which the company reported a $111 million funded backlog.

FEI’s Zyfer division supplies GPS and secure timing products; its Elcom Tech division makes electronic warfare and RF/microwave subsystems.

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