GNSS interference, misleading positions and reversion

How do jamming and spoofing differ?

Loss of a signal is easier to notice than a plausible false one.

Unavailable versus misleading

Jamming interferes with reception so that authentic GNSS signals may become unusable. Spoofing introduces deceptive signals that can make a receiver compute an incorrect position or time. The operational symptoms can overlap, and a cockpit symptom alone may not prove the precise mechanism. The key task is recognising suspect information and preserving control and a trustworthy navigation basis.

An unexpected position shift, implausible groundspeed or time, navigation disagreements or associated system anomalies deserve attention. GNSS feeds may support several functions, so a common disturbance can affect multiple outputs together. EASA and EUROCONTROL’s joint 26 March 2026 action plan addresses resilience; this lesson does not claim to identify every affected region or current event.

A smooth error can evade intuition

The laboratory contrasts loss of position with a slowly increasing false position. In the latter, a smooth map can drift away from independent radio/inertial information. The diagram labels true and reported positions as synthetic ground truth for learning; in flight the crew must infer the disagreement from available approved indications.

A slowly growing discrepancy

The synthetic aircraft follows a true straight path while a deceptive position drifts sideways by 0.1 NM each minute. After five minutes, the map shows a 0.5 NM displacement from independent ground-based geometry. The trace can be perfectly smooth because the error was introduced gradually. Looking only for a sudden jump would miss the growing disagreement.

If two navigation displays and a tablet share that source, they can show the same displaced track. Their agreement adds no independent range or bearing. A valid conventional aid or a suitably interpreted inertial solution may provide a different constraint, while ATC can help coordinate the resulting capability limitation. The crew need not prove the precise interference mechanism before treating the suspect information according to the approved procedure and preserving a safe navigation basis.

What makes a useful reversion independent?

Select a remaining capability that does not repeat the suspect measurement.

Control, cross-check and communicate

Maintain aircraft control and use the approved aircraft/operator procedures. Cross-check suspect position with suitable independent information such as valid conventional aids, inertial data interpreted for its drift, and available ATC assistance. Advise ATC of the navigation capability or information affected and coordinate a suitable path or approach.

Do not treat a second map application driven by the same GNSS source as independent. Also avoid assuming that all systems recover immediately when the interference ends: erroneous time or position may persist in some installations. Follow the specific restoration and sensor-selection procedure rather than improvising a universal reset.

Plan a capability, not a hopeful display

A reversion plan must fit actual service coverage, equipment, crew proficiency, fuel and procedure availability. A conventional ILS may avoid the affected final-approach position source, but routing to it, distance fixes or other system dependencies still need checking. The laboratory shows which sources remain available under explicit assumptions; it cannot certify a real aircraft’s degraded capability.

Rebuild the complete route to an approach

Suppose GNSS position is suspect and the destination offers an available ILS. Selecting ILS guidance may remove one dependency for final approach, but first ask how the aircraft will reach the localizer, which fixes or distances are required, whether DME is available and valid, and whether the remaining systems and crew support the operation. A final aid is only one part of the plan.

An inertial-only interval may be acceptable for a particular approved operation while uncertainty remains within its requirements, yet become unsuitable later. An ATC vector can also change the navigation task but depends on the service actually available and coordinated. Include fuel and alternate options in the decision. Reversion is an operational capability assessment built from current facts, rather than a universal instruction to switch one display source and continue unchanged.

Can you explain and apply the mechanism?

Four original questions. Work from the stated facts, then compare your reasoning with the explanation.