C H A P T E R

N ° 29

Avionics and Mitigation Measures (Part 2)

The aviation industry is within the top five sectors and industries most at risk from space weather impact. This is because of its heavy reliance on technology and infrastructure that can be disrupted by solar activities.

Solar activities can create space weather which can influence the performance and reliability of space-borne and ground-based technological systems and can, in some cases, even endanger human life or health.

The aviation industry is becoming more aware of the impact of space weather on flight operations due to the increase of cross-polar traffic. The industry is primarily concerned about risks during high-latitude (>50°N) and polar operations (>78°N). This is due to the South Atlantic Anomaly (SAA). Earth’s magnetic field is not truly dipolar in space or at the Earth’s surface. The internal magnetic field has a depression centered over the South Atlantic, which is known as the South Atlantic Anomaly (SAA). Solar activity causing a certain level of space weather can bring the magnetic field of Earth closer to the planet in this region. This means, that aircrafts flying only a few hundred kilometers above the mean surface level of Earth can experience exposure to a substantial radiation dose. The risks of space weather impact on aircrafts, pilots, and crew is, thus, the highest in these regions.

The industry has been subject to space weather impact numerous times with significant economic losses. In 2005, the total cost of extra fuel used to reroute aeroplanes from polar routes due to space weather amounted to approximately 186 million USD. This was excluding costs to passengers and compensation. The increased cross-polar traffic and economic losses makes space weather a recognized natural hazard within this critical infrastructure.

In Hoplon’ article C H A P T E R N ° 27, we provided a short introduction to the relation between space weather and the aviation industry, starting by exploring the interaction between space weather and the Earth’s natural planetary defence systems, and how they are connected to the potential space weather effects on the aviation industry. Additionally, we investigated the interdependencies between certain critical infrastructures and how this increased the risk and vulnerability to space weather impact on the aviation industry. The article ended with a short discussion providing some examples of the risks and effects experienced by the industry from space weather impact.

Space weather can affect aircrafts in various ways. Today’s article will be the second of two articles focused on avionics and mitigation measures. If the reader has not read part one; C H A P T E R N ° 28 , please feel free to do so before starting this one. In C H A P T E R N ° 28, we focused on space weather impact on High-Frequency (HF) communication and satellite navigation. In today’s article, we will look closer at: Automatic Dependent Surveillance Broadcast (ADS-B) and radar surveillance and avionics systems. Additionally, we will provide a short introduction to a well-known mitigation measure, that of; space weather forecast and warning systems.

**Image Credit:** Boldmethod; Flicker Deck.

Air transportation is highly sensitive to space weather effects and can be affected in various ways. Impact on the avionic systems and procedures include, but are not limited to; High-Frequency (HF) communication blackouts, satellite navigation failure, and surveillance failure.

Automatic Dependent Surveillance Broadcast (ADS-B) and radar surveillance failure

In order for air traffic managers to track aeroplanes and maintain safe separations they heavily rely on radar systems and the Automatic Dependent Surveillance-Broadcast (ADS-B) system.

The Automatic Dependent Surveillance-Broadcast (ADS-B) system onboard aeroplanes continuously transmit messages at 1.090 MHz. These are then received by other aeroplane and ground Automatic Dependent Surveillance-Broadcast (ADS-B) receivers providing air traffic control centres with information about aeroplane statuses, enabling them to manage air traffic.

This service is dependent on the Global Navigation Satellite System (GNSS). However, as previously discussed, space weather can disrupt the Global Navigation Satellite System (GNSS), consequently interfering with the signals distributed and received by the Automatic Dependent Surveillance-Broadcast (ADS-B) system leading to decreased functionality.

Furthermore, despite being rare, space weather can in some instances lead to the failure of radar-based surveillance. An example of this was on the 4’th of November 2015. During this time, a coronal mass ejection (CME) caused a geomagnetic storm, leading to severe disruption to secondary air traffic control radar systems in Sweden, Belgium, Norway, and Greenland. This disruption in radar systems occurred during a time when the antennas were pointed at the Sun, coinciding with a strong solar radio burst. The space weather event led to a temporary (~1 hour) closure of the southern Swedish airspace and delayed flights due to the inaccurate information received by controllers through the radar-based surveillance system.

Mitigation measures

When both radar and the Automatic Dependent Surveillance-Broadcast (ADS-B) systems become unavailable, a crucial fallback mechanism in aviation is the ‘procedural control’ – also known as ‘non-radar control’. This is a form of air traffic control where separation of aircraft is maintained without relying on the immediate visualization of aircraft provided by radar surveillance systems. Instead, they rely on the use of predetermined routes, time-based separation, or other non-radar methods. This mechanism, thus, ensure flight safety without a use of the satellite radar system.

However, the lack of radar and the Automatic Dependent Surveillance-Broadcast (ADS-B) systems create a necessity for even higher aircraft separation standard. This causes a reduction in airspace capacity and places greater workload demands on air traffic controllers. A disruption in surveillance systems can increase the workload and stress for air traffic controllers, further complicating air traffic management during adverse conditions and causing a compromise in efficiency levels and exacerbate fatigue among air traffic controllers, thereby increasing the likelihood of human errors.

The impact of space weather on the operational efficiency of air traffic controllers is challenging to quantify precisely. Nevertheless, its significance cannot be overlooked, as any resultant human-induced accidents could have severe consequences.

**Image Credit:** Aireon: *A diagram showing global space-based ADS-B coverage.*

Avionic system errors and failures

Space weather can cause radiation storms that can significantly elevate the risk of Single-Event Effects (SEE) in electronic systems onboard aircraft, particularly during high-altitude operations. Single-Event Effects (SEE) in avionics refer to the impact of high-energy particles like Solar Energetic Particles (SEPs), Galactic Cosmic Rays (GCRs), and neutrons, on electronic components in aircrafts.

These effects can cause malfunctions, data corruption, or even catastrophic failures. There are different types of Single-Event Effects (SEE): 1) A Single-Event Upset (SEU), caused by a single particle getting into the aircraft system, wherefrom it can flip a bit in memory, leading to data corruption; 2) A Single-Event Latch-up (SEL), caused by a particle getting into the aircraft system and thereby accidentally turns on a parasitic transistor, causing a high-current state and potentially damaging the device; 3) A Single-Event Burnout (SEB), caused by particles creating a localized high-current state that can destroy the device; and 4) a Multiple Bit Upset (MBU), caused by a particle interacting with the aircraft system, causing multiple bits to flip, potentially lading to more significant data errors.

Single-Event Effects (SEE) can affect various systems in aircrafts, including flight control computers, navigation systems, and data transmission buses. These effects can pose safety risks, especially in critical flight control systems, and require thorough assessment to ensure compliance with safety requirements.

An example of an in-flight upset due to Single-Event Upset (SEU) was the A330 incident in 2008. During this time, an unrealistic angle of attack (AOA) value was transmitted on the ARINC 429 bus, which is a data transfer standard for aircraft avionics using self-clocking and self-synchronizing data bus protocols. The angle of attack (AOA) value led to an unintended pitch-down maneuver. This is when the pilot lowers the nose of the aircraft. A pitch-down maneuver can be dangerous, especially if not intended, as it can lead to a loss of control or unexpected outcomes, consequently increasing the risk of a stall or ground contact.

The 2008 A330 incident was not directly caused by space weather. However, the same risk is possible during certain types of space weather events. It is, therefore, important to be aware of this risk.

Mitigation measures

To mitigate Single Event Effect (SEE) several strategies can be employed. These include but are not limited to: using radiation-hardened components, implementing redundancy, and employing error detection and correction techniques.

Radiation-hardened components are specifically designed and manufactured to withstand the effect of radiation, including Single Event Effects (SEE). This is usually done by utilizing materials, circuit designs, and manufacturing processes to minimize the impact of radiation. For example: the use of radiation-hardened microcontrollers or memory chips in avionic systems can minimize the impact of radiation to the electronic systems. Special shielding materials can physically block radiation from reaching sensitive components to a certain threshold by absorbing or deflecting the radiation. However, this type of mitigation measure can add weight and volume to the avionic system and may, therefore, not be feasible for all applications.

Redundancy is used to create duplicate or triplicate systems to ensure continued operation even if one component fails due to Single Event Effects (SEE). Triple Modular Redundancy (TMR) is a common form of redundancy, whereby three identical modules perform the same function, and a coting mechanism selects the output of the majority of the modules. For example: Triple Modular Redundancy (TMR) can be used for critical control systems or data storage in avionics. Additionally, redundancy testing can also be performed. This is a process where the backup or duplicate systems and components are tested and verified in case the primary system fails.

Error Detection and Corrections (EDAC) are used to detect and correct errors caused by Sing Event Effects (SEE). The error detection and correction (EDAC) codes add extra bits to data to allow for the detection and correction of errors. For example: Hamming codes can be used to detect and correct single-bit errors in memory.

Implementing different design techniques can additionally minimize the impact of Single Event Effects (SEE). For example:

Resistance Capacitance (RC) delay hardening: by adjusting circuit parameters, one can minimize the effects of transients pules, which is short-duration, high-amplitude voltage or current spikes that can disrupt or damage electronic systems.
Stacking transistors: by using multiple transistors in series to block current transients.
Careful circuit layout: certain layouts of circuits can minimize the susceptibility of sensitive nodes to radiation.

Furthermore, one can use software-based mitigation measures like the implementation of error detection and correction mechanisms within the software to furtherly increase resilience. For example: one can implement redundancy in software algorithms by using checksums to verify data integrity, and by implementing watchdog timers to reset the system in case the computer or software application becomes unresponsive to user input (i.e., hangs) or malfunctions occur due to a Single Event Effect (SEE).

Single Event Effects (SEE) should be considered from a system-level perspective. Designing the entire system with Single Event Effects (SEE) in mind, considering the interactions between different components and subsystems. This could be done by using a hierarchical design approach with fault-tolerant architecture and the implementation of robust error handling mechanisms. Additionally, testing is crucial for identifying Single-Event Effects (SEE) sensitivities and validating mitigation strategies. By conducting tests on components and systems, it ensures that the mitigation techniques are effective and that the system can withstand the expected radiation environment.

How does space weather disrupt satellite-to-receiver communications?

**Image Credit:** Shahzaib Tahir et al.: Aircraft Communication Wireless Technologies.

Satellites enabling services such as High-Frequency radio communication, navigation, the Automatic Dependent Surveillance Broadcast (ADS-B) system, or the radar surveillance system all depend on radio waves travelling from satellites in space through the near-Earth space environment and the atmospheric layers on Earth to the receivers on the ground or receivers in air, in case of for example a receiver onboard an aircraft. Thus, when the aviation industry uses High-Frequency (HF) radio communication it is using communication satellites.

This type of communication service enables a signal to be sent out, wherefrom it relies on it to be bounced off of the ionosphere and then get picked up by the receiver from the aeroplane or the air traffic controller located on the ground. The communication between pilot and air traffic controllers, thus, rely on this process.

The same process applies to other satellite services. All satellites rely on the process of sending and receiving radio waves that has to travel through the Earth’s atmospheric layers and the space environment in order to transmit and receive data (i.e., information).

However, space weather interferes with the environment that these radio waves have to travel through. An example of this is the capability of space weathers of increasing the atmospheric density, consequently enabling radio waves on their journey to or from a receiver to be absorbed or scattered by the atmosphere. When absorbed, the radio waves, thus, never reaches the receivers (i.e., the pilot or the air traffic control centre).

* To learn more about the relation between space weather and satellites, please read: C H A P T E R N ° 11. *

**Image Credit:** Christian Kissling: *aeronautical communication system*.

Mitigation measures

The loss of signals can be caused by multiple things other than space weather impact. The pilot and crew are, therefore, familiar and trained in what to do when losing a signal when operating. Mitigation measures are, thus, in place to enable a safe flight/landing. For example: the pilot will carry on flying the aircraft in the same flight path until it is able to communicate with the air traffic control room again.

However, if warnings and alerts have been provided beforehand about the risk of High-Frequency radio communication blackouts, aircrafts with transatlantic or polar routes are not permitted to take-off landing sites.

Space weather forecast and warning systems

Similar to terrestrial weather forecast and warning systems, space weather forecast and warning systems are likewise used by the aviation industry.

Terrestrial weather forecasts are used for all types of flight planning, whereas space weather forecasts and warnings are of particular importance for flight planning at high latitudes such as the polar routes.

However, this is only one mitigation measure within the multiple ones needed in order to keep pilots, crewmembers, passengers, and residential areas safe. Space weather forecasts and warnings is a tool that should be used as a guide for operators to figure out their next step in case of a space weather event and, thus, risk of space weather effects on avionics and pilot and crew flying transatlantic or through the Polar Regions.

Closing remarks

Space weather can cause operational issues due to its impact on the exterior and interior of aircrafts, and effect human health - the latter will be discussed in a future article. Flight dispatchers (i.e., flight operations officers), therefore, rely on numerous mitigation measures.

As mentioned, there are several backups and mitigation procedures depending on how flight-critical a system is. However, as technology progresses, flight electronics are becoming smaller and more advanced. This increases their vulnerability to space weather impact. The advancement of aviation technology, the changes in design, and the interdependencies within critical infrastructure increases the risk and vulnerability of space weather impact on the aviation industry.

Despite there being certain mitigation measures for this industry, it is not immune. Currently, during severe and extreme space weather events, most aircrafts are restricted from take-off. This is due to the high risks associated with space weather impact on the aviation systems and procedures. The need for novel and innovative mitigation measures within the aviation industry, therefore, remain.

* Flight-critical refers to aspects of a flight that are essential for safety and must be handled with utmost care. It encompasses critical phases of flight, critical parts of an aircraft, and critical tasks in maintenance, all of which, if compromised, could lead to serious consequences, such as accidents or even fatalities. *

**Image Credit:** Avionics Internaitonal.

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