This folder contains the ten canonical deep-dive files for the GNSS Resilience and APNT topic.

Files#

Reading Order#

For a first reading: overview then components then blocks. For operational planners: threads then modules then enablers. For performance reviewers: performance_objectives then timeline.

Source Basis#

• Doc 9849 (GNSS Manual), Fifth Edition, 2025 — primary ICAO reference.
• Annex 10, Volume I, Chapter 3, §3.7 — GNSS SARPs (Amendment 94, effective 27 November 2025, introduced ARAIM and DFMC provisions).
• EASA SIB 2022-02 Revision 3 (July 2024) — current European safety bulletin on GNSS jamming and spoofing.
• ICAO/ITU/IMO Joint Statement on Protecting GNSS from Harmful Interference, 2025.
• Doc 8168 (PANS-OPS) — procedure criteria for GNSS-based approaches; RAIM availability requirements.

What GNSS Resilience Is#

The Global Navigation Satellite System (GNSS) is the primary means of Position, Navigation and Timing (PNT) for civil aviation. PBN operations across en-route, terminal, and approach phases depend on GNSS; ADS-B and ADS-C surveillance rely on GNSS position; ATM system timing synchronisation depends on GNSS time signals.

GNSS Resilience is the capacity of this PNT capability to withstand, detect, and recover from disruptions. Disruptions fall into three classes: intentional interference (jamming — blocking signals; spoofing — replacing them with counterfeit signals); unintentional interference (radio frequency interference from non-aviation emitters, industrial equipment, personal privacy devices); and natural phenomena (ionospheric scintillation, solar radio bursts, space weather).

ICAO Doc 9849 (GNSS Manual, Fifth Edition, 2025) is the primary reference. Its opening summary states plainly that GNSS signals are vulnerable to intentional and unintentional interference and to certain natural phenomena, and that States manage this by controlling spectrum use, having contingency procedures, and retaining some conventional infrastructure.

Alternative Positioning, Navigation and Timing (APNT) is the complementary concept: it names the backup systems and strategies that sustain IFR operations when GNSS is unavailable or unreliable. The primary APNT tools are airborne IRS, DME/DME RNAV, the VOR Minimum Operational Network, ILS for precision approach, and emerging eLORAN for timing and en-route PNT.

The Threat Landscape#

For most of GNSS civil aviation history the interference threat was theoretical. That changed after 2022. Two drivers accelerated the risk:

The proliferation of inexpensive personal privacy devices (PPDs) — low-cost GPS jammers marketed to defeat vehicle tracking — produced a persistent background of unintentional interference near urban roads and airports.

The use of sophisticated military electronic warfare in active conflict zones created much larger-area intentional jamming and spoofing events with direct impacts on civil aviation. EASA SIB 2022-02 (first published March 2022, revised to R3 in July 2024) documented sharply increasing events in the Mediterranean, Black Sea, Middle East, Baltic Sea, and Arctic. GPS signal loss events increased approximately 220 percent between 2021 and 2024. Approximately 1,500 civil flights per day were experiencing spoofing by mid-2024. The ICAO 42nd Assembly (2025) formally condemned Russia for repeated deliberate GNSS interference affecting European airspace.

The threat is asymmetric: the attacker needs only a small, cheap transmitter to affect hundreds of aircraft across a large geographic area, while each affected aircraft must carry independent means of detection and fall-back.

Where GNSS Resilience Sits in the ICAO Framework#

GNSS resilience sits within the CNS (Communications, Navigation, Surveillance) pillar of the ASBU framework. The relevant ASBU thread is NAVS — Navigation Systems. Key modules:

• NAVS-B0 — basic single-constellation GPS/GNSS as primary means of navigation for PBN; ABAS/RAIM for integrity monitoring.
• NAVS-B1 — dual-constellation or dual-frequency GNSS; first SBAS APV approaches; DME network optimization to support RNAV fallback.
• NAVS-B2 — multi-constellation, multi-frequency (DFMC) GNSS as primary means of navigation; ARAIM; inherent resilience from signal diversity.

Resilience planning sits at the intersection of NAVS and the ASBU APNT concept (§7.13 of Doc 9849). It is not a separate ASBU thread — it is the risk-management dimension that determines how fast conventional aids can be rationalized without compromising fallback capacity.

The ICAO Assembly Resolution A32-19 (Charter on Rights and Obligations of States relating to GNSS) established the foundational principle: provider States must ensure reliability of GNSS services; all States have the right to non-discriminatory access; cooperation and mutual assistance in global planning are obligatory.

Relationship to Other Topics in this Workspace#

• PBN — all PBN navigation specifications with GNSS sensors depend on GNSS resilience; the fallback column of PBN planning is APNT.
• Airspace Design and Airspace Management — GNSS outage contingencies may require increased separation standards or airspace restrictions.
• ATFM — large-area jamming events reduce effective capacity in affected sectors and require ATFM flow management responses.
• VOR and NDB Requirements — the rationalization pace of the conventional navaid network is directly constrained by APNT coverage requirements.

References#

• Doc 9849 (GNSS Manual), Fifth Edition, 2025, Preface and Chapter 1 — scope, GNSS vulnerability statement, APNT definition.
• Doc 9849, Chapter 5, §5.1.3 — intentional interference and spoofing threat analysis.
• Doc 9849, Chapter 7, §7.13 — APNT strategy; GPS outage contingency.
• Annex 10, Volume I, Chapter 3, §3.7 — GNSS SARPs; ABAS, SBAS, GBAS; Amendment 94 ARAIM (27 November 2025).
• Assembly Resolution A32-19 — Charter on Rights and Obligations of States relating to GNSS Services (authoritative source — not in local library).
• EASA SIB 2022-02 Revision 3 (July 2024) — GNSS Outages and Alterations; current European safety bulletin (authoritative source — not in local library; https://ad.easa.europa.eu/blob/EASA_SIB_2022_02_R3.pdf/SIB_2022-02R3_1).
• ICAO/ITU/IMO Joint Statement on Protecting GNSS from Harmful Interference (2025) — five required Member State actions (authoritative source — not in local library; https://www.icao.int/sites/default/files/Meetings/a42/Documents/Protecting-GNSS-from-Harmful-Interference.pdf).

Top-Level Structure#

The GNSS resilience system has three top-level component groups:

• The GNSS signal infrastructure (core constellations and augmentations)
• Threat sources (what can disrupt the signal infrastructure)
• Detection and fallback systems (airborne and ground-based)

GNSS Resilience Architecture
|
+-- GNSS Core and Augmentations
|   +-- Core constellations (GPS, GLONASS, Galileo, BDS)
|   +-- ABAS (RAIM / ARAIM / AAIM)
|   +-- SBAS (WAAS, EGNOS, MSAS, GAGAN, KASS, BDSBASe, SDCM)
|   +-- GBAS (precision approach / GLS)
|
+-- Threat Sources
|   +-- Unintentional RFI (PPDs, industrial, DME/TACAN spectrum overlap)
|   +-- Intentional jamming (denial — signals blocked)
|   +-- Intentional spoofing (deception — false position output)
|   +-- Natural phenomena (ionospheric scintillation, solar radio burst)
|
+-- Detection and Fallback
    +-- Airborne integrity monitoring (RAIM / ARAIM)
    +-- Multi-sensor cross-check (GNSS vs IRS / GNSS vs DME-DME)
    +-- ATC cross-check (ADS-B vs SSR/PSR)
    +-- Ground monitoring (AUGUR, ICAO interference reporting)
    +-- APNT fallback (IRS, DME/DME RNAV, VOR MON, ILS, eLORAN)

GNSS Core Constellations#

Four ICAO-recognised core satellite constellations form the foundation:

• GPS (United States) — original civil aviation GNSS; L1 C/A and L5 signals.
• GLONASS (Russian Federation) — Channel of Standard Accuracy; FDMA scheme.
• Galileo (European Union) — Open Service; higher-power OS with Open Service Navigation Message Authentication (OSNMA) planned as an anti-spoofing tool.
• BDS (China, BeiDou Navigation Satellite System) — BDS-3 fully operational since July 2020; BDS Open Service offered to civil aviation from 2021.

Multi-constellation operation (DFMC — dual-frequency multi-constellation) is the primary GNSS self-resilience enhancement. Annex 10, Volume I, Amendment 93 (2023) introduced DFMC SARPs for GPS, GLONASS, Galileo, and BDS. Amendment 94 (effective 27 November 2025) added ARAIM provisions exploiting multi-constellation signals.

Augmentation Systems#

Three augmentation classes amplify GNSS performance and integrity:

Aircraft-Based Augmentation System (ABAS): airborne-only integrity monitoring using redundant satellite range measurements. Sub-types:

• RAIM (Receiver Autonomous Integrity Monitoring): GPS L1 C/A only; detects faulty satellite signals using geometry-based consistency check; requires at least 5 satellites for fault detection, 6 for exclusion (FDE). Defined in Annex 10 Vol I and Doc 9849, §4.2.2.
• ARAIM (Advanced RAIM): multi-constellation, single or dual-frequency; uses Integrity Support Data (ISD) broadcast from ground-based Integrity Support Message Generators (ISMGs); provides deeper fault coverage. Service Type A (defined in Annex 10 Amendment 94): supports en-route, terminal, and non-precision approach. Service Type B (future): intended for vertical guidance (precision approach equivalent).
• AAIM (Aircraft Autonomous Integrity Monitoring): inertial-aided; uses IRS to bound GNSS errors independently of satellite geometry.

Satellite-Based Augmentation System (SBAS): network of ground reference stations transmits corrections and integrity data via geostationary satellites. Supports APV (approach with vertical guidance) and CAT I equivalent minima. Regional SBASs: WAAS (US, operational 2003), EGNOS (Europe, operational 2011), MSAS (Japan, 2007), GAGAN (India, 2015), KASS (Republic of Korea, 2024), BDSBAS (China, expected 2025), SouthPAN (Australia/New Zealand, final certification expected 2028). DFMC SBAS: dual-frequency SBAS removes ionospheric delay and improves service in equatorial regions.

Ground-Based Augmentation System (GBAS): VHF data broadcast from a single airport station provides corrections and integrity for precision approach. Supports GLS (GBAS Landing System) operations. GBAS is resilient to ionospheric spoofing: GBAS data authentication makes spoofing of the ground broadcast extremely difficult.

Threat Types#

Unintentional RF Interference (RFI): signals not designed to disrupt GNSS. Primary sources are personal privacy devices (PPDs, vehicle tracking jammers), industrial emitters, and DME/TACAN spectrum overlap with GNSS L5 band. Spectrum management (ITU coordination, national regulations) is the primary preventive control. Multi-frequency receivers greatly reduce unintentional denial probability.

Intentional Jamming: deliberate broadcast of high-power RF signals in GNSS frequency bands to deny reception. Effect is conspicuous: receivers lose lock, RAIM alerts trigger, navigation mode degrades. Area of effect can be large (hundreds of NM for powerful military systems). Detection is immediate but the fallback to conventional navigation must be fast.

Intentional Spoofing: broadcast of counterfeit GNSS-like signals that cause receivers to compute an erroneous but apparently valid position. More dangerous than jamming because the receiver does not alert. The erroneous GNSS position propagates to FMS, ADS-B broadcast, and any GNSS-driven system without triggering integrity alarms. Detection requires cross-referencing an independent position source. Doc 9849 §5.1.3.5 identifies three detection mechanisms: IRS/GNSS position discrepancy, pilot instrument cross-check, ATC ADS-B vs SSR comparison.

Ionospheric Scintillation: rapid fluctuations of ionospheric electron density cause signal amplitude and phase variations. Worst in equatorial and high-latitude regions. L5 SBAS (dual-frequency) mitigates most of the effect; GBAS detects ionospheric gradients and stops approach service when the system cannot ensure integrity.

Airborne Detection and Mitigation#

RAIM/ARAIM provides autonomous on-board fault detection. When the protection level (HPL/VPL) computed from satellite geometry exceeds the alert limit for the intended operation, RAIM gives an alert and navigation guidance is withdrawn. Crews must then revert to conventional navigation or request radar vectoring.

Multi-sensor integration provides the key spoofing counter. Most transport aircraft carry an IRS that continues to produce position estimates independently of GNSS signals. When GNSS and IRS positions diverge beyond a threshold, the integrated avionics flag the GNSS solution as potentially invalid. DME/DME area navigation — where a multi-DME position fix is available — provides a third independent position reference.

Pilot procedures (as reinforced by EASA SIB 2022-02) require crews to: confirm that automatic reversion to conventional navigation is enabled (some aircraft default to GNSS-only mode); monitor for GNSS/IRS position discrepancies; report interference events promptly; be prepared to request radar vectoring if GNSS is unavailable or unreliable.

APNT Backup Systems#

IRS (Inertial Reference System): all transport aircraft carry at least one IRS. IRS position drifts with time (typically 1-2 NM/hour for modern laser ring gyro systems) but provides short-to-medium-term area navigation independent of any external signal. IRS coasting is the primary immediate fallback after GNSS loss.

DME/DME RNAV: multi-sensor FMS uses range measurements from two or more DME stations to compute area navigation position fixes. Supports RNAV 1/2 operations in en-route and terminal airspace where DME coverage is adequate. DME networks are being maintained and enhanced as the primary APNT infrastructure. Doc 9849 §7.13.2.4 identifies DME as the most appropriate conventional aid for near-to-mid-term PBN continuity.

VOR Minimum Operational Network (MON): a strategically planned residual VOR network that ensures en-route backup coverage. The MON concept, as described in Doc 9849 §7.14.3.7, ensures that VOR-equipped aircraft at or above 5,000 ft can navigate to an airport with an ILS or VOR approach within 100 NM. The FAA VOR MON programme (US) and the EUROCONTROL network rationalisation are the primary implementations.

ILS (Instrument Landing System): remains the primary conventional precision approach backup. Doc 9849 §7.13.2.4 states ILS is the most appropriate alternative for precision approach when GNSS is unavailable. Precision approach ILS capability is to be retained when operationally beneficial per Appendix F §1.2(d) of the GNSS Manual.

eLORAN (enhanced Long Range Navigation): low-frequency (100 kHz) terrestrial navigation operating independently of GNSS. Uses ground transmitters whose signals penetrate buildings and are highly resistant to jamming (much higher power than GNSS). UK committed GBP 155 million to a national eLORAN programme in 2025, targeting timing service synchronisation with national clock network by 2027. eLORAN provides en-route PNT and a GNSS-independent timing reference.

References#

• Doc 9849 (GNSS Manual), Fifth Edition, 2025, Chapter 4, §4.2.1 — ABAS integrity monitoring classes: RAIM, ARAIM, AAIM.
• Doc 9849, Chapter 4, §4.2.2 — RAIM algorithm, satellite geometry requirements (5 for FD, 6 for FDE), alert limits.
• Doc 9849, Chapter 4, §4.2.3 — ARAIM principles, Integrity Support Data (ISD), Service Types A and B.
• Doc 9849, Chapter 5, §5.1.1 — GNSS signal weakness; single-frequency vulnerability; multi-frequency resilience benefit.
• Doc 9849, Chapter 5, §5.1.3 — Spoofing taxonomy, detection mechanisms (IRS cross-check, ADS-B vs SSR, pilot monitoring).
• Doc 9849, Chapter 6 — SBAS systems (WAAS, EGNOS, MSAS, GAGAN, KASS, BDSBAS, SouthPAN); DFMC SBAS capability.
• Doc 9849, Chapter 7, §7.13 — APNT strategy; IRS coasting; DME/DME RNAV; VOR/DME backup; ILS precision approach retention.
• Annex 10, Volume I, §3.7 — GNSS SARPs; ABAS, SBAS, GBAS performance requirements and specifications.
• Annex 10, Volume I, Amendment 94 (effective 27 November 2025) — ARAIM Service Type A; DFMC provisions; SBAS and DME frequency updates.

The Defence-in-Depth Model#

Rather than ASBU availability windows, GNSS resilience is structured as a sequence of four defence-in-depth layers. Each layer provides a line of defence; the system degrades gracefully when a layer fails to prevent the threat from propagating to the next layer.

Layer 1 — Prevent#

The prevention layer aims to stop the interference from occurring or reaching the aircraft receiver.

Spectrum management is the primary State-level control: States must establish regulations conforming to ITU Radio Regulations that protect GNSS frequency allocations (1 559-1 610 MHz for L1, 1 164-1 215 MHz for L5/E5) from harmful interference. National laws banning personal privacy devices and prescribing severe penalties reduce the background RFI from PPDs.

Signal-level resilience through multi-constellation, multi-frequency reception makes denial substantially harder. Simultaneously jamming L1 and L5 bands across GPS, GLONASS, Galileo, and BDS is a much larger undertaking than jamming a single L1 GPS signal. This is the technical rationale behind the ASBU NAVS-B2 target of DFMC GNSS as primary navigation.

Galileo Open Service Navigation Message Authentication (OSNMA) is a cryptographic signal authentication scheme broadcast on the Galileo E1-B signal. It allows receivers to verify that received signals were genuinely transmitted by the Galileo system, making spoofing attacks that attempt to replicate Galileo signals detectable.

Military coordination: States authorising GNSS interference testing or operations must coordinate with ANSPs, publish NOTAMs, and assess civil aviation impact before execution. EUROCONTROL published guidelines on the civil-military coordination process for GNSS interference testing.

Layer 2 — Detect#

Detection is the most critical layer for spoofing, because a successful spoofing attack that is not detected can propagate to incorrect FMS routing, ADS-B position errors, and ATC conflict alerts.

Airborne detection via integrity monitoring: RAIM triggers when the horizontal protection level (HPL) exceeds the alert limit for the current operation (2 NM en-route, 1 NM terminal, 0.3 NM NPA final approach), indicating that a faulty satellite cannot be isolated with confidence. ARAIM uses multi-constellation signals and ISD to extend fault detection to more demanding operations.

Cross-sensor spoofing detection: IRS position and GNSS position are computed independently. When their difference exceeds a threshold, the FMS flags the GNSS solution as suspect. DME/DME position, if available, provides a third independent reference. These checks do not require any additional ground infrastructure.

ATC cross-check: controllers observing an aircraft whose ADS-B track deviates from the expected route, or whose ADS-B position diverges from SSR Mode C returns or PSR tracks, should suspect spoofing or navigation anomaly and coordinate with the crew.

Ground-based interference monitoring: EUROCONTROL AUGUR (Advanced GNSS User Receiver) network provides real-time interference event mapping. ICAO encourages States to deploy their own monitoring and to report events through the standardised GNSS interference reporting system. Doc 9849, Appendix F and §5.3 provide detailed guidance on monitoring system design and reporting formats.

Layer 3 — Mitigate#

Once an interference event is detected, the mitigation layer contains the impact and keeps operations as close to normal as possible.

Aircraft-level: pilots switch to conventional navigation mode (IRS coasting, DME/DME RNAV). Note that automatic reversion may be disabled by default on some aircraft types — EASA SIB 2022-02 explicitly instructs pilots to manually enable reversion if GNSS capability degrades.

ATC level: if widespread interference is confirmed, the responsible ANSP can activate flow management measures (ATFM regulation), increase separation standards in affected sectors, restrict access to high-density airspace, or close airspace where fallback navigation coverage is insufficient. NOTAMs describe the area and expected duration.

Coordination: the ANSP must inform adjacent ANSPs and relevant airlines promptly. If the interference originates from military activity, the ANSP should request immediate cessation or coordination with the authorising State authority.

Pre-planned contingency procedures: Doc 9849 §7.13.2.5 lists the factors that determine which procedure applies — airspace classification, radar availability, avionics capabilities of the fleet, ATC workload, and the impact on other GNSS-dependent functions (surveillance, timing).

Layer 4 — Fall Back (APNT)#

When mitigation is insufficient and GNSS remains unavailable, operations continue using APNT infrastructure. The capability available depends on the aircraft avionics, the phase of flight, and the ground infrastructure.

The minimum operational network concept in Doc 9849 §7.14.3.6 defines the residual conventional navaid infrastructure that must be maintained. Rationalization of VOR and NDB networks must stop at the point where the MON coverage requirement is still met — that is, where VOR-equipped aircraft can reach an ILS/VOR-equipped airport within 100 NM at or above 5,000 ft from any point in the airspace.

Maturity and ASBU Progression#

References#

• Doc 9849 (GNSS Manual), Fifth Edition, 2025, Chapter 5, §5.1 — threat taxonomy; unintentional, intentional, spoofing.
• Doc 9849, Chapter 7, §7.12 — GNSS monitoring and interference reporting.
• Doc 9849, Chapter 7, §7.13 — APNT strategy; contingency procedures; conventional aid retention.
• Doc 9849, Chapter 7, §7.14 — Conventional aid transition planning; minimum operational network; VOR MON example.
• Doc 9849, Appendix F — GNSS RFI Mitigation Plan; prevention, detection, and mitigation guidance for ANSPs.
• Annex 10, Volume I, Amendment 94 (27 November 2025) — ARAIM Service Type A; DFMC GNSS provisions.
• EASA SIB 2022-02 Revision 3 (July 2024) — pilot procedures for GNSS outages; conventional navigation reversion (authoritative source — not in local library).

Overview#

GNSS resilience work is organised across six functional threads. Each thread addresses a distinct axis of the problem. Taken together they span the full lifecycle from understanding the threat through protecting spectrum, detecting events, sustaining operations, and reporting.

Thread 1 — Threat Characterisation#

This thread covers what is known about the interference environment: sources, geographic distribution, growth trends, and the physics of how jamming and spoofing affect GNSS receivers.

Doc 9849 Chapter 5 provides the canonical taxonomy:

• Unintentional RFI from personal privacy devices (PPDs), industrial equipment, and DME/TACAN spectrum compatibility issues.
• Intentional jamming: denial of service over a geographic area.
• Intentional spoofing: three sub-types (S1 repeaters, S2 errant signals, S3 collateral spoofers) each with different receiver-level impacts.
• Natural phenomena: ionospheric scintillation and solar radio bursts.

Risk assessment methodology is covered in Doc 9849 Appendix F §5.3.2: probability and severity of interference are treated as dependent variables for intentional threats (high severity increases probability because it increases the attractiveness of the attack), which is a security-specific departure from the standard safety risk model.

Active threat intelligence feeds include EUROCONTROL AUGUR, IATA Flight Data Exchange interference reports, EASA SIB 2022-02 revisions, and the ICAO interference event database. The EUROCONTROL interference testing guide identifies that military peacetime testing can affect GNSS within a 300 NM radius of the transmitter.

Thread 2 — Airborne Resilience#

This thread covers what the aircraft itself does to detect, report, and respond to interference.

Integrity monitoring progression:

• RAIM (single-constellation GPS L1): available on virtually all IFR-approved GNSS receivers; requires 5+ satellites for fault detection, 6+ for FDE; protection level compared to alert limit per operation.
• ARAIM (multi-constellation, defined in Annex 10 Amendment 94, 2025): uses ISD from a ground-based ISM Generator; provides Service Type A for en-route through NPA; Service Type B for vertical guidance is deferred to a future SARPs amendment.
• AAIM: IRS-integrated integrity monitoring; the IRS provides an independent measurement that bounds GNSS errors.

Multi-sensor integration for spoofing detection: the FMS computes position from GNSS, IRS, and DME/DME independently. Cross-comparison thresholds are defined by avionics certification standards. When GNSS/IRS divergence exceeds the threshold the GNSS solution is flagged. In practice, IRS integration provides the most reliable spoofing indicator because IRS cannot be spoofed by radio signals.

Pilot procedures (EASA SIB 2022-02): manual enable of conventional navigation reversion where aircraft default to GNSS-only mode; active monitoring of IRS/GNSS discrepancy; reporting of interference events.

DFMC avionics (under ASBU NAVS-B2): receivers using L1+L5 signals from two or more constellations have intrinsically higher resilience. The additional frequency eliminates most unintentional interference and dramatically raises the difficulty of intentional jamming.

Thread 3 — Ground Backup Infrastructure#

This thread covers the physical infrastructure available when GNSS is unavailable.

DME network: the primary APNT layer for en-route and terminal operations. Multi-DME position fixing, used by FMS in RNAV 1/2 operations, requires a DME network dense enough to provide two-DME geometry coverage at all points in the intended operation. Doc 9849 §7.14.2 requires that DME network optimization accompany GNSS implementation, particularly where GNSS L5 band spectrum is shared with DME/TACAN. The FAA has a programme to replace and enhance approximately 124 DME facilities by 2035 to strengthen DME MON.

VOR Minimum Operational Network (MON): the VOR rationalisation strategy described in Doc 9849 §7.14.3.7 ensures that a residual VOR network provides en-route backup coverage. The specific MON standard (100 NM from an ILS/VOR airport at or above 5,000 ft for VOR-equipped aircraft) defines the floor below which the VOR network cannot be further reduced without degrading APNT coverage.

ILS retention: precision approach backup. Doc 9849 §7.14.3.5 confirms ILS is the primary source of precision approach guidance and will serve as the main backup to GNSS-based approaches for the foreseeable future. Doc 9849 Appendix F §1.2(d) requires States to retain essential conventional navigation infrastructure including ILS when operationally beneficial.

eLORAN: the emerging terrestrial PNT complement. eLORAN transmits at 100 kHz with megawatt-class transmitter power — orders of magnitude more powerful than GNSS signals. This makes eLORAN highly resistant to jamming. It provides PNT independent of any satellite system, with accuracy sufficient for en-route and area navigation. eLORAN also provides a GNSS-independent timing reference, addressing the timing resilience gap for ATM systems that depend on GNSS for UTC time. The UK programme (GBP 155 million committed in 2025) targets service from approximately 2028.

Thread 4 — Procedures and Contingency#

This thread covers how flight operations adapt when GNSS is degraded.

Pre-flight planning: crews verify RAIM availability for the planned route and destination; NOTAMs for known interference events are assessed; alternate airports with ILS or VOR approaches are selected.

In-flight response to jamming: when RAIM alerts trigger, crews announce to ATC, switch to conventional navigation mode, and request radar vectoring if required. ATC may apply increased separation.

In-flight response to suspected spoofing: when IRS/GNSS discrepancy is observed without a RAIM alert (the spoofing indicator), crews cross-check all available navigation sources, inform ATC, and revert to conventional navigation. ATC correlates ADS-B with SSR/PSR.

ANSP contingency: Doc 9849 §7.13.2.5 requires ANSP contingency procedures that account for: radar availability; avionics mix (proportion of fleet with IRS and DME/DME capability vs GNSS-only); ATC workload capacity; impact on ADS-B surveillance.

Large-area outages (conflict zone events): the ANSP may implement ATFM flow restrictions in affected sectors to maintain safe separation given reduced navigation precision. Airspace restrictions may be issued for operations requiring GNSS-dependent procedures with no available fallback.

NOTAM management: Doc 9849 §7.11 establishes GNSS NOTAM standards for outage prediction and reporting. Military authorities operating jamming equipment must coordinate with ANSPs and publish NOTAMs covering the affected area, duration, and size.

Thread 5 — Reporting and Monitoring#

This thread covers collection, sharing, and analysis of interference event data.

Crew reporting: EASA SIB 2022-02 and Doc 9849 Appendix F §5.3 encourage crews to file interference event reports using a standard form (Doc 9849 includes a sample interference report card in Appendix F). Reports should cover the event location, duration, affected systems, and actions taken.

ANSP reporting to ICAO: ANSPs aggregate event reports and submit to the ICAO GNSS interference database. The data supports global threat mapping and identifies systematic sources.

Ground-based interference monitoring: fixed monitoring stations (such as those deployed as part of EUROCONTROL AUGUR and ICAO/APAC regional deployments) detect and geolocate interference sources. Synergies between GNSS performance monitoring and interference detection are encouraged by Doc 9849 §7.8.

EUROCONTROL AUGUR: provides real-time mapping of GNSS interference events in European airspace. Operational since 2015; significantly expanded after 2022. Feeds into EASA SIB revision process.

IATA Flight Data Exchange: collects interference event data from over 300 operators; provides regional and route-pair granularity for risk assessment.

Thread 6 — Spectrum Protection#

This thread covers the regulatory and enforcement framework for protecting GNSS frequency bands.

ITU coordination: GNSS frequency allocations (L1, L5/E5, L2 bands) are protected under the ITU Radio Regulations. States must implement frequency regulations in conformance with ITU. Spectrum compatibility studies are required before new systems are deployed in or near GNSS bands.

National legislation: Doc 9849 §5.1.4.4 recommends that States ban ownership, import, export, manufacture, sale, and use of jamming and spoofing devices. Enforcement programmes should include capability to detect interference sources.

DME compatibility: Doc 9849 §5.1.2.6 notes that high-density DME networks near the L5/E5 band can create interference at altitude; network optimisation (balancing DME station density) is required as DFMC avionics uptake grows. Amendment 94 to Annex 10 included DME frequency assignment planning updates to address this interaction.

Road tolling and tracking systems: Doc 9849 §5.1.4.5 recommends that non-aviation GNSS-based fee collection systems be designed to detect and resist jamming (so that users have no motivation to use PPDs to avoid fees), reducing the background PPD threat.

References#

• Doc 9849 (GNSS Manual), Fifth Edition, 2025, Chapter 5, §5.1 — threat taxonomy; unintentional, intentional jamming, spoofing.
• Doc 9849, Chapter 5, §5.1.4 — legal and regulatory framework; PPD bans; spectrum coordination.
• Doc 9849, Chapter 7, §7.11 — GNSS NOTAM standards; outage notification requirements.
• Doc 9849, Chapter 7, §7.12 — monitoring and interference reporting; AUGUR synergies.
• Doc 9849, Chapter 7, §7.13 — APNT strategy; IRS, DME/DME, VOR/DME, ILS layering.
• Doc 9849, Chapter 7, §7.14 — Conventional aid transition and rationalisation to minimum operational network.
• Doc 9849, Appendix F — GNSS RFI Mitigation Plan; ANS provider obligations; prevention, detection, mitigation, response.
• Annex 10, Volume I, Amendment 94 (27 November 2025) — ARAIM; DFMC GNSS; DME frequency assignment planning.
• EASA SIB 2022-02 Revision 3 (July 2024) — recommended crew procedures; monitoring and reporting (authoritative source — not in local library).
• EUROCONTROL GNSS Interference Testing Guide v2.0 (2023) — civil-military coordination process for GNSS interference testing (authoritative source — not in local library; https://www.eurocontrol.int/sites/default/files/2023-03/eurocontrol-gnss-interference-testing-guide-v2-0.pdf).

Focus Module: GNSS Outage Reversion to DME/DME + VOR MON#

This file works through one representative mitigation strand in detail: what happens when a GNSS jamming event is detected en-route, and how the aircraft and ATC revert to DME/DME RNAV with the VOR Minimum Operational Network as the secondary backup.

This is the most common required APNT scenario: aircraft in controlled en-route airspace, carrying IRS and FMS with multi-DME capability, losing GNSS while in a region where the VOR MON has been maintained.

Scenario Setup#

• Flight: IFR, RNAV 2 route, FL350 in controlled upper airspace.
• Aircraft avionics: triple IRS, FMS with multi-DME capability (RNAV 1/2), GNSS primary navigation sensor (single-constellation, L1 C/A), no L5.
• Infrastructure: adequate DME coverage for RNAV 2 along the route; VOR MON in place — airport within 100 NM with ILS approach.
• Threat: military GNSS jamming exercise not fully coordinated with the ANSP, affecting a 200 NM radius area.

Step 1 — Detection#

The aircraft GNSS receiver loses satellite lock as the jamming signal rises. RAIM detects that HPL has exceeded the 2 NM en-route alert limit because fewer than the required minimum satellites with good geometry are available. A RAIM/GPS alert annunciates on the PFD.

Simultaneously, the FMS notes that the IRS-computed position and the GNSS-computed position have diverged beyond the FMS cross-check threshold (this divergence may occur before RAIM alerts in a partial jamming scenario where the receiver is degraded rather than fully denied).

The crew sees: RAIM alert; possible FMS position caution; navigation mode in the FMS may downgrade from RNP to RNAV or conventional.

Step 2 — Airborne Reversion#

The FMS automatically shifts to a multi-DME RNAV position fix using the two highest-geometry DME stations in range. The IRS provides attitude and short-term position continuity. The FMS now computes position from DME/DME updating of the IRS.

The navigation mode displayed changes from GPS/GNSS RNAV to DME/DME RNAV (or IRS/DME in some avionics). The navigation accuracy is now RNAV 2 (2 NM total system error, 95 percent) if adequate DME geometry is present.

Doc 9849 §4.2.1.5 notes: IRS or DME-updating can be used to coast through short periods of poor satellite geometry or jamming. The combination of GNSS FD or FDE with IRS accuracy mitigates signal jamming effects.

If the aircraft type has automatic reversion disabled by default (some aircraft types do), the pilot must manually select conventional navigation mode per EASA SIB 2022-02 guidance.

Step 3 — ATC Notification and Coordination#

The crew contacts ATC: "Centre, [callsign], GNSS/RAIM unavailable, switching to DME/DME RNAV, request confirm radar contact."

ATC confirms radar identification on SSR Mode C. The controller notes that the ADS-B track and SSR track are consistent (the reversion is to DME/DME, not a spoofing scenario, so there is no position discrepancy).

ATC notes the event and checks whether other aircraft in the area are reporting similar anomalies. If multiple aircraft report GNSS loss, the sector supervisor activates contingency procedures: possible radar- mandatory sector, possible increase to non-RNAV separation standards for aircraft without DME/DME fallback capability.

Step 4 — En-Route Continuation under DME/DME RNAV#

The aircraft continues the route using the DME/DME RNAV position. RNAV 2 accuracy is maintained. ATC provides conventional radar service, with separation based on SSR Mode C altitude.

If the DME network provides adequate geometry (two DME stations with greater than 30-degree angular separation and within 130 NM), RNAV 2 is sustained throughout the jamming area. Typical European and North American DME networks were designed with this fallback in mind.

If DME geometry degrades at some point along the route, the FMS reverts to pure IRS dead-reckoning. IRS position error accumulates at approximately 1-2 NM per hour. ATC radar vectoring compensates for growing position uncertainty: the controller provides track guidance rather than relying on the aircraft's self-contained RNAV.

Step 5 — Approach Planning Revision#

As the aircraft approaches the destination, the crew assesses which approach type is available:

If GNSS remains unavailable and SBAS is also affected: GNSS-based approaches (RNAV(GNSS), LPV) are not available.

Primary fallback: ILS approach. The destination has an ILS CAT I installation (retained under the MON/ILS retention policy of Doc 9849 §7.14.3.5 and Appendix F §1.2(d)). Crew selects ILS approach. ILS is independent of GNSS — it uses VHF localiser and UHF glidepath radio signals. Unaffected by GNSS jamming.

Secondary fallback: VOR approach. The VOR MON ensures that a VOR is within range. VOR approach minima are higher (lower cloud base and visibility requirements) than ILS CAT I. Acceptable as a non- precision approach contingency.

ATC notifies the crew of the available approaches and clears the ILS approach. Normal ILS landing.

Step 6 — Post-Event Reporting#

After landing, the crew files an interference event report covering:

• Location and time of GNSS loss onset and recovery.
• Aircraft systems affected (GNSS, ADS-B position source, FMS mode).
• Actions taken (DME/DME reversion, ATC coordination, approach type used).
• Estimated area of jamming effect based on loss/recovery position.

The report is submitted through the national ASR/ECCAIRS system and aggregated into the ICAO interference database and EUROCONTROL AUGUR. Doc 9849 Appendix F provides a standard interference report form.

Variations on the Module#

The same sequence applies with different fallback steps depending on aircraft equipment:

Aircraft without multi-DME FMS capability: IRS coasting only after GNSS loss. Position error accumulates. ATC radar vectoring is mandatory throughout. Approach: ILS or radar approach only.

Aircraft with L5 DFMC receiver (ASBU NAVS-B2): jamming at L1 alone may not prevent GNSS operation on L5. The aircraft continues GNSS navigation on L5, possibly switching to single-frequency mode with degraded performance. The probability of complete denial is reduced.

Spoofing scenario (GNSS/IRS position discrepancy without RAIM alert): the crew recognises the IRS/GNSS divergence, confirms with ATC that the ADS-B position appears inconsistent with radar, declares GNSS unreliable, and reverts to DME/DME RNAV. The distinction from jamming is that the GNSS receiver is still providing an output — but an erroneous one that must be actively rejected.

References#

• Doc 9849 (GNSS Manual), Fifth Edition, 2025, Chapter 4, §4.2.1.5 — IRS and DME/DME integration; coasting capability.
• Doc 9849, Chapter 5, §5.1.3.5 — Spoofing detection; IRS/GNSS divergence; ATC cross-check.
• Doc 9849, Chapter 7, §7.13.2.4 — DME as primary APNT for PBN; VOR/DME en-route backup; ILS for precision approach.
• Doc 9849, Appendix F — GNSS RFI mitigation plan; interference report form (Appendix to Appendix F).
• Doc 8168 (PANS-OPS), Volume I, Part III — criteria for ILS, VOR, and RNAV approach procedures.
• EASA SIB 2022-02 Revision 3 (July 2024) — pilot guidance; conventional navigation reversion; event reporting (authoritative source — not in local library).

Overview#

Six categories of enabler determine whether an ANSP or State can implement effective GNSS resilience and APNT: avionics and CNS infrastructure; procedures and training; spectrum regulation; certification and standardisation; institutional coordination; and financing.

1. Avionics and CNS Infrastructure#

Multi-sensor FMS: the airborne backbone of APNT is a flight management system capable of accepting position inputs from multiple independent sources — GNSS, IRS, multi-DME, and in future eLORAN receivers. Most modern transport aircraft carry this capability, but many regional and general aviation aircraft rely exclusively on GNSS, and do not carry IRS or multi-DME navigation. The proportion of the fleet with adequate fallback capability is the primary constraint on the pace at which conventional aids can be rationalized.

DFMC receivers (L1+L5, multi-constellation): avionics certified to receive and process dual-frequency signals from two or more constellations are the primary GNSS self-resilience enhancement. These avionics also enable ARAIM (Annex 10 Amendment 94, 2025). Fleet replacement and certification cycles typically span 10-20 years; wide uptake of DFMC avionics will not be complete until the mid-2030s.

DME ground infrastructure: the network must be maintained, and strategically enhanced where rationalisation of VOR has reduced navaid density. The FAA has committed to replacing approximately 100 legacy DMEs with up to 124 new units by 2035 to sustain the DME MON. European ANSP networks require similar maintenance. New DME frequency planning (Annex 10 Amendment 94) addresses spectrum compatibility with GNSS L5.

ILS ground infrastructure: precision approach fallback capability. Must be retained at airports designated as alternates in the MON. ILS maintenance and replacement is the primary infrastructure enabler for precision approach APNT.

eLORAN transmitter network: currently under development in the UK (GBP 155 million programme committed 2025). Will require coordinated deployment across multiple States for full coverage. Receivers will need to be incorporated into new avionics TSOs. Not expected to be operational before 2028.

2. Procedures and Training#

Crew training on GNSS vulnerability: EASA SIB 2022-02 identified a training gap — many crews were unaware of spoofing symptoms (in particular, that IRS/GNSS divergence without a RAIM alert is the key indicator). Operators must include interference scenarios in recurrent training and simulator programmes.

Standard operating procedures for GNSS degradation: operators must have written procedures for RAIM alert response; for spoofing detection; for conventional navigation reversion; and for interference reporting. These procedures must be tested in simulator.

ANSP controller training: controllers in high-risk areas (conflict zone proximity) must be trained to recognise multi-aircraft GNSS degradation events, apply appropriate separation standards, and coordinate with the military authority where jamming is state- authorised.

Pre-flight RAIM prediction: RAIM availability prediction is an operational requirement for GPS NPA. Pilots must confirm RAIM will be available for the intended operation. Many EFB applications and ANSP services provide RAIM prediction tools.

Contingency procedures publication: ANSPs must publish contingency procedures (in the AIP or equivalent) for operations in the event of GNSS outage, identifying which routes can be flown using DME/DME RNAV or conventional navigation, which approaches have ILS or VOR fallback, and what the ATC procedures are for a large-area outage.

3. Spectrum Regulation#

ITU frequency allocation protection: the GNSS L1 and L5 bands must be protected under national frequency regulations consistent with ITU Radio Regulations. Coordination with military spectrum managers is required to minimise interference from military systems.

PPD prohibition: States must enact and enforce legislation prohibiting personal privacy devices. Enforcement requires: customs interception of imported devices; national legislation with appropriate penalties; and road-mobile monitoring capability to detect and locate active PPDs near airports. Most developed States have PPD legislation; enforcement quality varies widely.

Military testing coordination: States with military GNSS jamming testing programmes must coordinate with their ANSPs and publish NOTAMs before testing. The EUROCONTROL GNSS Interference Testing Guide provides a recommended coordination process.

4. Certification and Standardisation#

RAIM and ARAIM: Annex 10 Vol I §3.7 provides the normative GNSS SARPs. ARAIM Service Type A (Amendment 94, 2025) is now normative; avionics must be certified against relevant TSO/ETSO standards. RTCA and EUROCAE update MOPS to reflect amendment content.

Multi-sensor navigation TSOs: FAA TSO-C115B and EASA ETSO-C115 define the standards for multi-sensor FMS capable of IRS/DME/GNSS integration. These TSOs are the certification basis for DME/DME RNAV capability.

GBAS authentication: the GBAS data broadcast authentication scheme, described in Doc 9849 §5.1.3.8, makes GBAS spoofing extremely difficult and provides a precision approach technology with inherent anti-spoofing properties. GBAS CAT II/III SARPs (Annex 10 Vol I, Amendment 91 onwards) support precision approach down to zero visibility.

5. Institutional Coordination#

ICAO Navigation Systems Panel (NSP): develops GNSS SARPs, ARAIM service definitions, and interference guidance. NSP/7 (2025) produced Amendment 94.

EUROCONTROL GNSS interference working groups: coordinate the European AUGUR network, GNSS testing guidelines, and ANSP contingency planning across the ECAC area.

ICAO/ITU/IMO Joint Statement (2025): the inter-agency coordination mechanism for spectrum protection and contingency infrastructure. The five required State actions provide the policy mandate.

Military-civil coordination: the primary institutional gap. The EUROCONTROL process provides a framework for peacetime testing. Wartime or conflict-zone interference requires diplomatic coordination that aviation alone cannot achieve — it is a whole-of-government issue. ICAO Assembly resolutions (including the 2025 condemnation of Russia) provide political leverage.

State safety programmes: GNSS vulnerability assessment should be an explicit element of each State's safety risk picture. States that have not conducted a formal GNSS vulnerability assessment per Doc 9849 §7.13 are at risk of being unable to demonstrate APNT compliance during ICAO USOAP audits.

6. Financing#

Conventional aid maintenance: DME and ILS installations have 20-25 year replacement cycles. Investment decisions must account for the role of these aids in the APNT architecture, not just their current traffic value. Without explicit APNT funding mechanisms, navaid operators may rationalise aids below the MON threshold.

eLORAN investment: building a national eLORAN network requires significant upfront capital. The UK programme (GBP 155 million) demonstrates that Government must lead this investment. Regional coordination (sharing transmitter infrastructure) can reduce per- country costs.

ARAIM ground infrastructure (ISMGs): the Integrity Support Message Generator network for ARAIM requires States and constellation providers to fund and operate the ISMGs for each constellation (one ISMG per constellation, operated under aviation authority jurisdiction). This is a new funding obligation introduced by Amendment 94.

References#

• Doc 9849 (GNSS Manual), Fifth Edition, 2025, Chapter 4, §4.2.3 — ARAIM architecture; ISMG funding and operation.
• Doc 9849, Chapter 7, §7.13 — APNT strategy; IRS/DME avionics dependency; fleet capability assessment.
• Doc 9849, Chapter 7, §7.14 — Conventional aid transition planning; rationale for retaining DME, ILS.
• Doc 9849, Appendix F, §1 — ANSP obligations for RFI mitigation plan; State obligations for spectrum and infrastructure.
• Annex 10, Volume I, Amendment 94 (27 November 2025) — ARAIM; ISMG obligations; DME frequency planning.
• Doc 8168 (PANS-OPS), Volume I — RAIM availability as pre-flight requirement for GNSS NPA procedures.
• EASA SIB 2022-02 Revision 3 (July 2024) — operator and crew training obligations; procedure requirements (authoritative source — not in local library).
• EUROCONTROL GNSS Interference Testing Guide v2.0 (2023) — military-civil coordination framework (authoritative source — not in local library).
• UK Government eLORAN Programme commitment (2025) — GBP 155 million; national PNT resilience strategy (authoritative source — not in local library; https://insidegnss.com/uk-commits-155-million-to-eloran-timing-and-gnss-monitoring-in-major-pnt-resilience-push/).

The Performance Lens#

GNSS resilience sits primarily within the Safety, Continuity, and Capacity KPAs of the ICAO ATM performance framework (Doc 9854 / Doc 9883). Unlike most ATM improvements that advance multiple KPAs, GNSS resilience is a risk-management and contingency measure: its primary benefit is the prevention of safety-critical navigation failures, with secondary benefits for capacity (maintaining throughput during interference events) and cost-effectiveness (by preserving efficient operations in degraded modes).

Key Performance Areas (KPAs) Applicable to GNSS Resilience#

KPA Contribution by Resilience Layer#

The following matrix scores each KPA by its benefit from each of the four defence-in-depth layers. Scores: 1 = some benefit, 2 = clear benefit, 3 = primary driver.

Performance Objectives#

PO-1: Zero GNSS-caused Controlled Flight into Terrain (CFIT) or loss of separation#

Primary KPA: Safety. Rationale: GNSS integrity failure (undetected spoofing or jamming- induced position error) is a precursor to CFIT on instrument approaches and loss of separation in enroute operations. RAIM/ARAIM, multi-sensor cross-check, and ILS precision approach retention are the barriers. Measured by: loss-of-navigation events per million approaches; incidents where GNSS error was a contributing factor; navigation system RAIM alert rate in affected areas.

PO-2: Sustained IFR operations through GNSS outage events#

Primary KPA: Continuity. Rationale: GNSS denial should not cause widespread flight diversions or airspace closure. APNT infrastructure (DME/DME RNAV, VOR MON, ILS) sustains operations when GNSS is unavailable. Measured by: proportion of IFR operations completing without diversion during documented GNSS outage events; proportion of airports within APNT coverage at the time of an outage. Target: 100 percent of airports with IFR approaches have a non-GNSS approach procedure (ILS, VOR, NDB, PAR) as fallback.

PO-3: Interference events detected and reported within 15 minutes#

Primary KPA: Safety / Monitoring. Rationale: rapid detection limits the exposure of aircraft to jamming or spoofing. Reporting enables fleet-wide warnings and NOTAM issuance. Measured by: mean time from onset of interference event to first ATC awareness; proportion of interference events resulting in an ICAO interference report within 24 hours.

PO-4: Minimum operational network maintained for all rationalisation plans#

Primary KPA: Access and equity. Rationale: the Doc 9849 §7.14.3.7 MON standard (VOR coverage at or above 5,000 ft to a 100 NM ILS/VOR airport) must be met before any further VOR can be decommissioned. Similarly, DME density must sustain RNAV 2 fallback before GNSS sole-means operations are declared. Measured by: MON coverage compliance percentage; airports with no non- GNSS instrument approach available.

PO-5: Sector capacity maintained at 80 percent of nominal during GNSS events#

Primary KPA: Capacity. Rationale: a well-prepared ANSP should be able to maintain most IFR capacity using DME/DME RNAV and radar vectoring, avoiding the capacity collapse that would result if all aircraft were unable to navigate. Measured by: ATFM regulation rate attributable to GNSS interference events; mean sector capacity reduction during documented interference events.

Key Performance Indicators#

Safety KPIs#

• Number of navigation anomalies where GNSS error was a contributing factor, per million flight hours (target: trend to zero).
• RAIM alert rate in documented interference zones, normalised per flight.
• Number of go-arounds or missed approaches attributed to GNSS unavailability, per 1,000 approaches in affected areas.

Continuity KPIs#

• Proportion of IFR flights completing to destination without GNSS- related diversion during documented outage events (target: >99%).
• Number of airports without a non-GNSS instrument approach procedure (target: zero for all airports with IFR operations above a defined threshold traffic level).

Monitoring KPIs#

• Proportion of interference events with a crew report filed within 24 hours (target: >80%).
• Number of States operating a ground-based GNSS interference monitoring capability (target: universal in ECAC; growing globally).

MON coverage KPIs#

• Percentage of airspace (area, measured at FL100) providing RNAV 2 fallback via DME/DME (target: >98% in en-route controlled airspace).
• Number of VOR decommissioning proposals reviewed for MON compliance before approval (target: 100%).

Capacity KPIs#

• Peak ATFM delay minutes attributable to GNSS interference events per year (trend metric: ideally decreasing as resilience matures).
• Mean sector capacity during documented interference events as a percentage of nominal (target: >80% where DME coverage is adequate).

Benchmark Statistics (2023-2025 context)#

These figures are drawn from EASA, EUROCONTROL, and IATA reporting and represent the scale of the current problem:

• GPS signal loss events increased approximately 220% between 2021 and 2024 (ICAO/IATA data, 2025).
• Approximately 1,500 civil flights per day were experiencing GNSS spoofing by mid-2024 (EASA SIB 2022-02 R3 context).
• Airbus recorded approximately 50,000 GNSS interference events on its aircraft in 2023, more than four times the 2022 figure.
• From June 2022 to June 2023, 209 airlines reported approximately 150,000 GPS loss events in 5 million flight operations (IATA FDX).

These figures illustrate that the performance gap between the current situation and the objectives above is substantial, and that the urgency of GNSS resilience investment is high.

References#

• Doc 9849 (GNSS Manual), Fifth Edition, 2025, Chapter 7, §7.13 — APNT strategy; resilience performance considerations.
• Doc 9849, Chapter 7, §7.14.3.6 — Minimum operational network concept.
• Doc 9854 (Global ATM Operational Concept), Chapter 2 — KPA definitions and ATM performance framework.
• Doc 9883 (Manual on Global Performance of the Air Navigation System) — KPI definitions and performance measurement methodology (authoritative source — not in local library).
• Annex 10, Volume I, Chapter 3, §3.7, Table 3.7.2.4-1 — GNSS availability specifications; performance requirements by phase of flight.
• EASA SIB 2022-02 Revision 3 (July 2024) — interference event scale; context for benchmark statistics (authoritative source — not in local library).
• IATA Safety Risk Assessment — GNSS Interference V5 (2024) — statistical analysis; FDX reporting data (authoritative source — not in local library).

Historical Evolution#

The table below is keyed by year and covers the key events in GNSS civil aviation adoption, the emergence of the interference threat, ICAO regulatory responses, and APNT infrastructure decisions.

Regulatory Milestone Summary#

References#

• Doc 9849 (GNSS Manual), Fifth Edition, 2025, Foreword — edition history; scope of 2025 revision.
• Annex 10, Volume I, Amendment table (lines 580-735 of the local library copy) — complete amendment history with dates.
• Annex 10, Volume I, Amendment 94 (effective 27 November 2025) — ARAIM, DFMC, DME frequency planning.
• EASA SIB 2022-02 Revision 3 (July 2024) — interference event chronology (authoritative source — not in local library; https://ad.easa.europa.eu/blob/EASA_SIB_2022_02_R3.pdf/SIB_2022-02R3_1).
• ICAO/ITU/IMO Joint Statement on Protecting GNSS from Harmful Interference (March 2025) — (authoritative source — not in local library; https://www.icao.int/sites/default/files/Meetings/a42/Documents/Protecting-GNSS-from-Harmful-Interference.pdf).
• ICAO 42nd Assembly Working Paper WP/34 (2025) — GNSS interference and protection measures (authoritative source — not in local library).

Primary ICAO Documents (in local library)#

• Doc 9849 (GNSS Manual), Fifth Edition, 2025 — the primary ICAO reference for all GNSS civil aviation topics including interference, augmentation, APNT, and conventional aid transition planning.
• Doc 9849, Chapter 4, §4.2.1 — ABAS integrity monitoring classes: RAIM, ARAIM, AAIM; redundancy and fault detection principles.
• Doc 9849, Chapter 4, §4.2.2 — RAIM algorithm; satellite geometry requirements (5 for fault detection, 6 for FDE); alert limits by operation.
• Doc 9849, Chapter 4, §4.2.3 — ARAIM principles; Integrity Support Data (ISD); ISMG architecture; Service Types A and B.
• Doc 9849, Chapter 5, §5.1.1 — GNSS signal weakness; single-frequency vulnerability; multi-frequency and multi-constellation resilience benefits.
• Doc 9849, Chapter 5, §5.1.3 — Intentional interference (jamming) and spoofing; taxonomy; detection via IRS/DME-DME cross-check; ADS-B vs SSR cross-check.
• Doc 9849, Chapter 5, §5.1.4 — Regulatory responses to intentional interference; PPD bans; enforcement; spectrum coordination.
• Doc 9849, Chapter 6 — SBAS systems; DFMC SBAS; regional providers (WAAS, EGNOS, MSAS, GAGAN, KASS, BDSBAS, SouthPAN).
• Doc 9849, Chapter 7, §7.11 — GNSS NOTAM standards; interference notification.
• Doc 9849, Chapter 7, §7.12 — Monitoring and interference reporting; AUGUR synergies; monitoring system design.
• Doc 9849, Chapter 7, §7.13 — APNT strategy; IRS, DME/DME, VOR/DME, ILS layering; contingency procedures.
• Doc 9849, Chapter 7, §7.14 — Conventional aid transition planning; minimum operational network; VOR MON concept; DME enhancement for RNAV.
• Doc 9849, Chapter 7, §7.15 — Programmatic and security aspects; GNSS service interruption in emergency situations.
• Doc 9849, Appendix F — GNSS Radio Frequency Interference Mitigation Plan; ANSP and State obligations; threat monitoring; risk assessment; interference report form.
• Annex 10 (Aeronautical Telecommunications), Volume I, Chapter 3, §3.7 — GNSS Standards and Recommended Practices; ABAS, SBAS, GBAS augmentation requirements; performance requirements by phase of flight (Table 3.7.2.4-1).
• Annex 10, Volume I, Appendix B, §3 — GNSS technical specifications for core constellations and augmentation systems.
• Annex 10, Volume I, Attachment D — Guidance on GNSS SARPs application; ABAS (§5), SBAS (§6), GBAS (§7); ionospheric effects (§3); interference (§10).
• Annex 10, Volume I, Amendment 93 (2023) — DFMC GNSS provisions; GPS L5, Galileo, BDS, GLONASS multi-constellation and dual-frequency SARPs; L5 SBAS provisions.
• Annex 10, Volume I, Amendment 94 (effective 27 November 2025) — ARAIM Service Type A; ISMG obligations; DME frequency assignment planning; GBAS and SBAS updates.
• Doc 8168 (PANS-OPS), Volume I, Part III — GNSS approach procedure criteria; RAIM availability as operational prerequisite for GNSS NPA and approach operations.
• Doc 9854 (Global ATM Operational Concept), Chapter 2 — KPA framework; ATM performance ambitions within which GNSS resilience is a CNS enabler.

ICAO Documents (not in local library — authoritative sources)#

• Assembly Resolution A32-19 — Charter on Rights and Obligations of States relating to GNSS Services; primacy of safety; provider State obligation for reliability; State sovereignty; non-discriminatory access (authoritative source — not in local library; https://www.icao.int/Meetings/AMC/MA/32/wp_a32-19.pdf).
• Doc 9750 (GANP), 7th Edition — ASBU NAVS thread; NAVS-B2 multi-constellation, multi-frequency GNSS as primary navigation target; conventional navaid rationalization strategy (authoritative source — not in local library; https://ganpportal.icao.int/).
• Doc 9883 (Manual on Global Performance of the Air Navigation System) — KPI definitions; performance measurement methodology for safety, continuity, capacity (authoritative source — not in local library).
• ICAO/ITU/IMO Joint Statement on Protecting GNSS from Harmful Interference (March 2025) — five required Member State actions; conventional navigation infrastructure retention obligation (authoritative source — not in local library; https://www.icao.int/sites/default/files/Meetings/a42/Documents/Protecting-GNSS-from-Harmful-Interference.pdf).
• ICAO 42nd Assembly Working Paper WP/34 (2025) — formal condemnation of Russia for GNSS jamming; resilience resolution (authoritative source — not in local library; https://www.icao.int/sites/default/files/Meetings/a42/Documents/WP/wp_034_en.pdf).

EASA Regulatory Material (authoritative sources — not in local library)#

• EASA SIB 2022-02 (17 March 2022) — GNSS Outages and Alterations Leading to CNS Degradation; first issue (https://ad.easa.europa.eu/blob/EASA_SIB_2022_02.pdf/SIB_2022-02_1).
• EASA SIB 2022-02 Revision 1 (17 February 2023) — first update following escalation in conflict zone interference (https://ad.easa.europa.eu/blob/EASA_SIB_2022_02R1.pdf/SIB_2022-02R1_1).
• EASA SIB 2022-02 Revision 2 (6 November 2023) — second update; spoofing scenarios added (https://ad.easa.europa.eu/blob/EASA_SIB_2022_02R2.pdf/SIB_2022-02R2_1).
• EASA SIB 2022-02 Revision 3 (July 2024) — current edition; documents 220% increase in GPS loss events 2021-2024; approximately 1,500 flights/day spoofing (https://ad.easa.europa.eu/blob/EASA_SIB_2022_02_R3.pdf/SIB_2022-02R3_1).

EUROCONTROL Material (authoritative sources — not in local library)#

• EUROCONTROL AUGUR GNSS interference monitoring system — real-time interference event mapping for European airspace (https://www.eurocontrol.int).
• EUROCONTROL GNSS Interference Testing Guide v2.0 (2023) — civil-military coordination process for planned GNSS interference testing; coordination process; NOTAM requirements (https://www.eurocontrol.int/sites/default/files/2023-03/eurocontrol-gnss-interference-testing-guide-v2-0.pdf).

FAA Material (authoritative source — not in local library)#

• FAA APNT DME/DME White Paper (2012) — US APNT strategy; DME/DME RNAV as near-term GPS backup; MON design principles (https://www.faa.gov/sites/faa.gov/files/about/office_org/headquarters_offices/ato/20120723APNT_DMEWhitePaper_dc.pdf).

UK Government (authoritative source — not in local library)#

• UK Government PNT Resilience Programme (2025) — GBP 155 million commitment to eLORAN, GNSS monitoring, and national timing infrastructure (https://insidegnss.com/uk-commits-155-million-to-eloran-timing-and-gnss-monitoring-in-major-pnt-resilience-push/).

IATA Material (authoritative source — not in local library)#

• IATA Safety Risk Assessment — GNSS Interference V5 (2024) — statistical analysis of FDX interference data; 150,000 GPS loss events in 5 million flight operations June 2022 to June 2023 (https://ic.iata.org/sites/default/files/iata_sih_document_attachment/IATA%20Safety%20Risk%20Assessment%20-%20GNSS%20Interference%20V5.pdf).