GNSS Phraseology - Say What the Problem Is

John FRANKLIN • 3 August 2026

in community Air Operations

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Recommended Phraseology for GNSS Jamming and Spoofing

GNSS jamming and spoofing are no longer rare operational anomalies.

Across parts of Europe, the Mediterranean, the Middle East and areas surrounding conflict zones, flight crews are increasingly encountering navigation degradation, map shifts, false positioning, spurious warnings and loss of RNAV capability linked to GNSS interference.

As these events become more common, one thing has become increasingly clear:

Clear communication matters

During high-workload situations, pilots and air traffic controllers need to understand quickly what the aircraft is experiencing, how navigation capability has been affected and what operational support may be required.

To support this, EASA has published recommended phraseology in an update of Safety Information Bulletin (SIB) 2022-02R4. The objective is simple. To encourage the use of clear, consistent language that helps crews and controllers rapidly build shared situational awareness during GNSS interference events.

Recommended phraseology

The phraseology recommended in the SIB focuses on describing the operational impact, rather than simply stating that there is a GPS problem.

Loss of RNAV capability

When the aircraft can no longer maintain the required RNAV or RNP capability due to GNSS interference, the recommended phraseology is:

"UNABLE RNAV DUE TO GPS INTERFERENCE"

"UNABLE RNP (type) DUE TO GPS INTERFERENCE (SPOOFING or JAMMING)"

These calls immediately tell ATC that navigation capability has been degraded, the cause is related to GNSS interference and alternative handling or vectoring may be required.

Suspected spoofing

Spoofing can be particularly challenging because aircraft systems may continue to appear normal while displaying incorrect position or timing information.

Where crews suspect spoofing, the SIB recommends identifying this clearly:

"GNSS UNAVAILABLE DUE TO SUSPECTED SPOOFING"

This allows controllers to anticipate possible navigation inconsistencies and helps build a common operational picture.

Spurious terrain warnings

One of the more challenging effects of GNSS interference can be false or misleading TAWS "PULL UP" warnings.

The recommended phraseology includes:

"GNSS PULL UP, PASSING 500 FEET DUE TO GNSS INTERFERENCE"

This enables crews to communicate the situation clearly while maintaining situational awareness and avoiding unnecessary confusion during already demanding phases of flight.

Time anomalies

Some spoofing events have also resulted in incorrect system time being displayed.

The SIB recommends reporting this using a simple but important phrase:

"TIME IS 13:13:31 NOW"

Although unusual, incorrect time information may provide an important indication that GNSS spoofing is affecting aircraft systems.

Good communication supports good decision-making

The recommended phraseology is not simply about choosing the right words.

It supports effective Crew Resource Management by reducing ambiguity, lowering workload and helping pilots and controllers develop a shared understanding of the situation.

Alongside the recommended phraseology, flight crews should continue to:

Aviate first.
Cross-check navigation sources.
Clearly assign crew roles.
Avoid fixation on a single system.
Communicate early with ATC.

Recognition alone is not enough. Crews should stabilise the operation, verify aircraft position using all available means and communicate clearly before navigation errors or separation risks increase. Controllers also play a vital role by recognising the recommended phraseology, providing vectoring where appropriate and sharing situational awareness across sectors.

Report and learn

Prompt reporting remains an essential part of managing GNSS interference.

EASA encourages crews and operators to submit AIREPs and occurrence reports whenever GNSS interference is encountered. High-quality reporting helps identify affected areas, understand operational trends, improve mitigations and strengthen resilience across the aviation system.

As GNSS interference becomes part of the operational environment, learning from every event helps improve safety for everyone.

The GNSS Phraseology Safety Map

Using the recommended phraseology is about more than communication. It supports effective teamwork, shared situational awareness and better operational decision-making throughout the aviation system.

🧠 Mindset

Expect GNSS interference to create uncertainty as well as technical challenges. Clear communication helps crews and controllers build a common understanding of the situation quickly.

👥 People

Pilots, air traffic controllers, dispatchers and operational teams all play a role. Effective Crew Resource Management and early communication reduce workload and support better decision-making.

⚙️ Equipment

Understand how aircraft systems behave during GNSS degradation and recognise the operational effects that may indicate jamming or spoofing. Cross-check all available navigation sources.

📋 Compliance

Follow operator procedures and apply the recommended phraseology published in EASA SIB 2022-02R4 to communicate operational limitations clearly and consistently.

⚠️ Risks

GNSS interference often occurs alongside other operational pressures such as weather, congestion or high workload. Clear communication helps prevent these risks from compounding.

📚 Learning

Report GNSS interference through occurrence reporting systems and AIREPs where appropriate. Every report contributes to a better understanding of evolving threats and supports improvements across the aviation system.

Further information

The article is supported by EASA's GNSS Interference video series, which demonstrates realistic operational scenarios covering spoofing, jamming and the use of the recommended phraseology.

Further guidance is available through:

As the operational environment continues to evolve, clear communication, good preparation and effective collaboration remain fundamental to managing GNSS interference safely.