Solar Cycle 25 Peak Disrupts GPS Accuracy for Aviation

The peak of Solar Cycle 25, now forecast for 2025–2026, has already produced multiple high-intensity solar radio bursts that directly degraded GPS satellite signals. FlySafe analysis shows that four significant radio emission events at GNSS frequencies have occurred since this cycle began — a pace that demands sustained attention from flight operations departments, dispatchers, and pilots relying on satellite navigation for precision approaches and en-route guidance.

This bulletin examines the mechanisms by which solar activity degrades aviation navigation, reviews recorded events from the current cycle, and outlines recommended operational responses based on publicly available data.

How Solar Activity Degrades GPS Navigation

Global Navigation Satellite Systems, including GPS, depend on radio signals transmitted from medium-Earth orbit satellites to ground-based or airborne receivers. These signals pass through the ionosphere — a layer of the atmosphere where solar radiation ionizes gas molecules, creating free electrons that alter signal propagation speed. The total number of free electrons along the signal path, known as Total Electron Content (TEC), varies with solar activity. As noted in documentation from the Space Weather Information Centre, neglecting changes in TEC "can introduce tens of meters of error in the position calculations" for GPS and GNSS systems.

Standard GPS receivers compensate for ionospheric delay using the Klobuchar model, a mathematical approximation of average ionospheric conditions. However, during periods of elevated solar activity, actual ionospheric conditions deviate significantly from this model's predictions. When conditions deviate from those predicted by the Klobuchar model, GPS/GNSS systems produce larger positioning errors — a particularly consequential outcome during instrument approaches where vertical accuracy requirements are measured in meters, not tens of meters.

Two distinct solar phenomena create navigation hazards:

Ionospheric disturbances from coronal mass ejections and geomagnetic activity alter TEC unpredictably, degrading the accuracy of position solutions across broad geographic regions.

Solar radio bursts (SRBs) emit intense radio energy at or near the frequencies used by GNSS satellites (around 1.2 and 1.6 GHz). These bursts can overwhelm receiver front-ends, reducing signal-to-noise ratios and causing satellites to drop from the navigation solution entirely.

Recorded Events in Solar Cycle 25

Solar Cycle 25 has already produced notable disruptions. According to data compiled by the Space Weather Information Centre, four strong radio emission events at GNSS frequencies have been recorded so far in this cycle:

• 13 June 2022 — Solar flux reached 98,000 solar flux units (sfu)
• 28 August 2022 — Solar flux peaked at 230,000 sfu, with a reported fading of 13 dB at the GPS L2 frequency
• 4 May 2023 — Solar flux reached 26,000 particle flux units (pfu)
• 14 December 2023 — Solar flux peaked at 99,000 sfu

The 28 August 2022 event warrants particular attention. A 13 dB fading at the L2 frequency represents a reduction in signal power by a factor of approximately 20. The L2 frequency is critical for dual-frequency receivers that use the difference between L1 and L2 signals to compute real-time ionospheric corrections. When L2 fades significantly, these receivers lose their primary method of compensating for ionospheric error, reverting to less accurate single-frequency solutions or losing position lock entirely.

For context, SKYbrary notes that the previous solar cycle (24) was of moderate intensity, with its peak observed in early 2014. Cycle 24's relative mildness may have produced complacency in operational planning. As one agricultural GPS analysis from the University of Georgia observed, "GNSS outages from solar storms should be expected as the norm during solar maximums," with the mild activity of Cycle 24 described as "abnormal." Aviation operations should calibrate expectations accordingly.

Impact on Aviation Navigation Systems

En-Route and Terminal Area Operations

Degraded GPS accuracy during solar events affects operations at every phase of flight, though consequences scale with the precision required. En-route navigation tolerances are relatively forgiving; a position error of several meters is operationally insignificant at cruise altitude with radar monitoring. The concern intensifies during terminal area operations and, most critically, during GPS-based instrument approaches.

According to Stanford University research on SBAS systems, the Localizer Performance with Vertical Guidance (LPV) approach — the most precise GPS-based procedure commonly flown — uses a Vertical Alert Limit of 50 meters and a Horizontal Alert Limit of 40 meters to guide aircraft down to 250 feet above ground level. When ionospheric disturbances push position errors toward or beyond these thresholds, the system must either alert the pilot or the approach becomes unavailable.

Disruptions can range from accuracy degraded from a few inches to several feet, to cases where GPS receivers may be unable to achieve a position lock at all. For airports where GPS-based approaches are the only instrument procedure available — increasingly common at smaller facilities — loss of GPS integrity can effectively close the airport to instrument traffic.

Augmentation System Vulnerabilities

The Wide Area Augmentation System (WAAS), developed by the Federal Aviation Administration, uses a network of 38 precisely surveyed Wide Area Reference Stations across North America to detect and correct GPS signal errors. Under normal conditions, GPS/WAAS receivers can achieve position accuracy of a few meters across the National Airspace System.

However, as the FAA's own documentation acknowledges, the WAAS service area and coverage quality change over time due to "satellite geometry and ionospheric conditions." During geomagnetic disturbances, the ionospheric correction models that WAAS broadcasts may lag behind rapidly changing conditions. A forward-looking study published in the AGU journal Space Weather by Xue et al. (2023) explored the potential effects of satellite navigation failure in 2025 from an aviation network perspective and proposed constructive Air Traffic Management measures to address potential satellite navigation failures during the solar maximum period.

Similar augmentation systems worldwide — Europe's EGNOS, India's GAGAN, Japan's MSAS — face analogous vulnerabilities during elevated solar activity periods.

Research Quantifying Signal Degradation

A study published in the Journal of Space Weather and Space Climate investigated the impact of the 20 most intense 1.4 GHz solar radio bursts from Solar Cycle 24 on the International GNSS Service GPS network. The research measured degradation across three parameters: degradation of satellite signal strength, reduction in the number of available satellites, and degradation of satellite geometry measured by geometric dilution of precision (GDOP). All three parameters directly affect the quality of navigation solutions available to aviation users.

Affected Airspace and Operational Considerations

Space weather effects on GPS are not confined to specific FIRs or routes — they are inherently global, affecting the sunlit hemisphere during solar radio bursts and producing broader effects during geomagnetic disturbances. However, certain operational contexts create elevated risk:

Polar and high-latitude routes. Ionospheric disturbances are most severe at high geomagnetic latitudes, where auroral and polar cap effects amplify TEC variability. Airspace status for polar routes (e.g., the North Atlantic Organized Track System, Pacific polar crossings) may require particular attention during geomagnetic activity periods. Recommendation: operators on high-latitude routes should monitor NOAA Space Weather Prediction Center advisories and ensure contingency navigation procedures are current.

Oceanic airspace with limited radar coverage. Where ATC radar surveillance is unavailable, GNSS-based position reporting is the primary means of maintaining separation. Degraded GPS accuracy in these regions reduces the reliability of automatic dependent surveillance (ADS) position reports.

Airports relying solely on GPS approaches. Facilities without conventional ground-based instrument landing systems (ILS) or VOR approaches become operationally limited when GPS integrity is compromised.

Affected routes during solar events can include any segment where performance-based navigation (PBN) or Required Navigation Performance (RNP) procedures depend on GPS as the sole positioning source.

Recommendations for Operators and Flight Crews

Based on publicly available NOTAMs, ICAO advisories, and augmentation system performance data, the following operational measures are appropriate during periods of elevated solar activity:

Monitor space weather forecasts. NOAA's Space Weather Prediction Center issues warnings, watches, and alerts for solar radio bursts, geomagnetic activity, and solar radiation events. ICAO's space weather information service provides aviation-specific advisories through designated global and regional centers.

Verify approach availability. Before commencing GPS-based approaches during active space weather events, crews should confirm RAIM (Receiver Autonomous Integrity Monitoring) prediction availability and be prepared to execute conventional approaches or divert to airports with ground-based navigation aids.

Maintain conventional navigation proficiency. Airlines have rerouted or adjusted operations during previous solar events. Operators should ensure that VOR, DME, and ILS-based procedures remain current in flight management systems and that crews maintain proficiency in non-GPS navigation.

Review contingency procedures for oceanic operations. Operators conducting extended oceanic flights should review contingency procedures for loss of GNSS-based ADS, including HF radio position reporting protocols.

Cross-reference multiple navigation sources. Where equipped, flight crews should monitor multiple navigation sources (GPS, inertial, ground-based) simultaneously to detect degraded GPS performance before it affects flight path accuracy.

Looking Ahead Through the Solar Maximum

FlySafe analysis indicates that the risk period extends well beyond the calendar peak of Solar Cycle 25. SKYbrary notes that for Solar Cycle 24, the period from 2011 to 2017 saw the highest occurrence and severity of solar eruptions, as these events are most likely during the maximum activity period and the following decreasing phase. If Solar Cycle 25 follows a similar pattern, elevated space weather risk to aviation GPS systems will persist through approximately 2028–2029.

The aviation industry's increasing dependence on satellite navigation — now embedded in everything from en-route separation standards to surface movement guidance — means that the consequences of GPS degradation are more operationally significant than during any previous solar cycle. Constructive ATM measures, as proposed in recent academic research, may need to become standard components of airspace management during solar maximum periods.

Operators, ANSPs, and regulators are encouraged to treat space weather as a routine operational variable — not an exotic edge case — for the duration of this solar maximum and its declining phase.

Analysis based on publicly available data only. FlySafe Research does not possess, access, or utilize any classified or non-public information. All sources referenced are independently verifiable through the linked publications and official databases.

Frequently Asked Questions

How much does an uncorrected ionospheric disturbance typically degrade GPS accuracy?

According to space weather research documentation, neglecting changes in the ionosphere's Total Electron Content during solar disturbances can introduce tens of meters of error in GPS position calculations. Under severe conditions, receivers may lose position lock entirely, making navigation solutions temporarily unavailable.

Why must commercial airlines avoid polar routes during geomagnetic and solar radiation storms?

High-latitude airspace experiences the most intense ionospheric disturbances during geomagnetic activity, which degrades GPS accuracy disproportionately in polar regions. Additionally, reduced HF radio propagation at high latitudes can compromise communication with ATC, and elevated radiation exposure at flight altitudes above polar regions may exceed recommended crew dose thresholds. These combined factors make rerouting a standard precautionary measure.

Can aviation crews detect when space weather is affecting navigation system accuracy in real-time?

Modern avionics with RAIM capability can detect when GPS integrity falls below required thresholds and will alert the crew. However, RAIM detects the result of degradation rather than its cause, and there may be a latency between the onset of a solar event and a RAIM alert. Cross-referencing GPS positions with inertial navigation or ground-based navaids remains the most reliable method for crews to independently verify navigation accuracy during suspect conditions.