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Manipulated GNSS Signal: implications for pilots

We are on the precipice of a new battleground, one invisible to the naked eye yet alarmingly present in its potential to disrupt the very foundation of global transportation—spoofing attacks on aircraft navigation systems. Spoofing, often confused with jamming, poses a far more insidious risk. It is not merely about obscuring a signal, but actively taking control of an aircraft's navigation, potentially leading to catastrophic misdirection.

This article outlines the differences between spoofing and jamming. It also provides pilots with an overview of the potential impact that both threats can have on their flights.  

Distinguishing Spoofing from Jamming

Manipulated Global Navigation Satellite Systems (GNSS) signals can compromise aircraft navigation systems, potentially leading to complete navigation loss, with severe safety implications. 

Satellite-based navigation systems are vulnerable to different attacks due to their low transmission power. There is a difference between two basic GNSS attack scenarios: GNSS Jamming and Spoofing. 

GNSS Jamming is the deliberate blocking of GNSS signals due to other transmitting devices, e.g. Software-defined radio transmitters, that can be used to transmit signals within the GNSS frequency range. In the past specific areas in the world experienced jamming quite regularly, e.g. the Korean Border. However, Jamming is not in particular special to conflict zones, personal privacy devices can be bought without restriction, for example preventing supervisors tracking lorry drivers. While disruptive, jamming is not as precise or potent as spoofing.

GNSS spoofing is a more refined and dangerous attack. The spoofer specifically targets certain aircraft and tries to influence the satellite-calculated position by altering and transmitting false satellite signals. For this kind of attack, the spoofer needs to know the position of the aircraft and can send the false signal to influence the aircrafts’ flight path. 

The people who carry out spoofing attacks are likely to be more than mere technology buffs; they could well be state actors or terror organizations with substantial resources and a specific agenda. Secondly, the distinction matters in the theater of airline security policy—countermeasures for jamming, while somewhat effective, fall short in combating spoofing.

Within most aircraft avionics the FMS (Flight Management Computer) position is regularly updated by IRS (laser guided gyros) and GNSS to ensure the highest accuracy. Losing the GNSS signal, an IRS would compute its position from the last known position.
In many aircraft avionics architectures, the FMS position utilizes both the IRS and GNSS to ensure the highest accuracy. Usually, IRS tend to drift away over time while being continuously available. On the other hand, GNSS provide position information, that does not drift away but may be subject to occasional outages.

Losing the GNSS signal, the FMS would continue to use the IRS and its last known position. When in range of conventional ground-based radio navigation devices (e.g., VOR, DME), it would utilize these to enhance the IRS location.

However, some avionics architectures feed the GNSS position directly into position computation. This may result in discarding the IRS position for navigational purposes, and/or directly utilizing the spoofed GNSS location for location determination. Thus, these systems are highly susceptible to GNSS spoofing attacks without giving any warning to the pilots. 

Potential consequences

Manipulated GNSS signals can disrupt aircraft navigation systems by: 

  1. Loss of GNSS as the navigation source: Loss of GNSS can affect the aircraft's navigation accuracy and integrity. This results in unsafe maneuvering in busy airspaces, flying close to terrain and performing GNSS based landing and departure systems.
  2. Misleading Positioning: Malicious actors may spoof misleading position data into the navigation system, potentially causing the aircraft to deviate from its intended route. This can become a big threat when flying close to borders of conflict zones and close to high terrain.
  3. Approach and Landing Hazards: Manipulated signals during critical phases of flight, such as approach and landing, can lead to unstable approaches or missed approaches, increasing the risk of accidents.
  4. Spurious Warnings: Some aircraft systems utilize the GNSS position directly. For example, systems that warn us when we fly towards mountainous terrain. The predictive modes of the TAWS (Terrain Avoidance and Warning System) may trigger false warnings as they are fed directly with the raw GNSS position. As false warnings occur, genuine ones may not, subjecting aircraft to more safety hazards. This could have a long-lasting effect on the crew's trust in the aircraft’s warning systems: a pilot receiving a false warning due to system position inaccuracy may be tempted to disregard a similar – but real – warning later. Moreover, false warnings increase pilot workload and could cause distraction during critical phases of flight.

Recommended actions

European pilots encourage aircraft manufacturers and operators to make a risk assessment determining if safe operations can be guaranteed through regions where GNSS signals are likely to be manipulated. Just as important is to establish appropriate crew operating procedures and training. These procedures should guarantee safe operation even in case of GNSS spoofing attacks. The best way to ensure that flight crew can handle these situations is through proper training.

As a result of GNSS signal loss or degradation, it is important for pilots to consider the following:

  • Review any technical, operations and safety bulletins issued by the aircraft manufacturer and your company manuals. When routes are planned through geographical regions where such manipulation is expected, operators should ensure that flight crews are informed about the threat and former incidents.
  • Brief each other.  Consider the potential risks associated with signal loss or degradation, and the impact this may have on systems requiring GNSS data such as falls warnings.
  • Pilots need to make sure that they constantly monitor the aircraft equipment performance closely for any discrepancies or anomalies.
  • Consider the use of non-GNSS-based navigation systems as much as feasible where it is allowed.

The potential for manipulated GNSS signals to compromise aircraft navigation systems is a serious safety concern. All stakeholders in aviation, including pilots, air traffic controllers, and regulatory authorities, should work together to raise awareness, enhance training, and take proactive measures to safeguard the integrity of navigation signals and ensure the safety of air travel. European pilots believe that future systems in civil aviation need to ensure a more robust system architecture using state-of-the-art cyber-security measures. However, considering the long lifecycles in aviation, a technical solution for a more robust and immutable satellite position signal may lie behind the horizon for a long time.

Further reading & sources

IFALPA + EASA Safety Bulletin

GPS spoofing 

GNSS jamming

Briefing Leaflet with effects