Environmental control systems for aircraft need to be robust, lightweight and high performance. Usually they are forgotten by travelers. But the ventilation of aircraft cabins during covid brought them to the forefront and the Center for Disease Control and National Institute of Health added comments about these aircraft systems on their websites. Now that travel is recovering, the focus is on innovation and efficiencies.
Environmental control systems are amongst the most energy demanding systems on aircraft. They typically rank at number one in terms of power draw from the engines over the aircraft life cycle. It is no surprise that much of the effort on the advances of these systems is concentrated on making them more energy efficient. Industry experts provide an update on the technological advances of environmental control systems.
Technological Advancements and the Pandemic
According to Laurent Hartenstein, expert fellow at Liebherr-Aerospace Toulouse’s engineering directorate, the technologies used in environmental control systems are highly dependent on the high-level aircraft and engine design choices. “Besides, thermal management of new power systems (batteries, fuel cells, high by-pass ratio engines, etc.), and the associated consuming systems have become a large contributor of potential optimization, with direct links to functions or technologies used in environmental control systems,” he says. “Technological advances in environmental control system are therefore requiring large panel technology advances to support various needs at equipment and system level and at system integration level. At equipment and system level, the needs are to support increased efficiency of products, for example by developing energy recovery modules in the turbomachine to recover the otherwise wasted thermal, or cabin pressure energy. At system integration level the need is to design optimum thermal management between heating and cooling power sources or means available on aircraft.”
Laurent Hartenstein Liebherr-Aerospace
Technological advancements have improved the robustness and the reliability of cabin environmental systems, according to Andreas Bezold, Cabin Air Quality & Ventilation Systems Expert at Airbus. “Reducing the fuel consumption of the ECS with more energy efficient system design is another essential design objective. This is reflected in our latest R&T projects focusing on this design parameter primarily. This also includes modifications in the frame of maintaining our cabin air quality standards, investigating the use of improved filtration devices,” he says. “The pandemic has led to increased R&T efforts focusing on air distribution patterns, infection risks in aircraft cabins etc. R&T efforts are continuing on sanitizing surfaces.”
The pandemic has put a lot of public focus on cabin air quality as a key topic for environmental control systems design, affirms Hartenstein. “Although airplanes already display ‘indoor’ environment superior to that available in our everyday life, several avenues are being investigated to further address this demand: with new architectures of systems using air supply directly taken from outside the cabin, and compressed, or with enhanced cabin air filtration systems, such as volatile organic compound (VOC) or high efficiency particulate air (HEPA) filters,” he says.
HEPA filters have been common for quite some time on commercial narrow body and wide body aircraft, observes Teledyne. “Plenty of existing information has been written describing the advantages of HEPA filters, particularly during the Coronavirus pandemic, but what has not been documented in detail is the airlines’ ability to monitor the effectiveness of their HEPA filters, i.e., are they blocked with particulates and require changing, and how the airlines are monitoring their effectiveness,” says Teledyne. “The only way to answer those questions is with a cabin air quality monitoring system – which is why we developed the ACES solution in order to aid airlines in answering these questions in addition to providing confidence for the traveling crew and passengers, that the environment they are in is safe.”
HEPA Filters
HEPA filters are standard on almost all commercial aircraft produced today, starting back in the 1990s, observes Teledyne. “Aircraft not equipped with HEPA tend to be older generation aircraft. The advantage of HEPA filters is their ability to capture or block very small particles. As it relates to COVID-19, with an approximate size of 100 nanometers, the typical HEPA filter easily captures particles with 99.9% efficiency, down to 10 nanometers (HEPA filters actually increase in efficiency while in use). Good practice when replacing a HEPA filter would include gloves and a N95 mask,” says Teledyne.
While the HEPA concept is still the most efficient and practical method for removing dust and pathogens from air since decades, some enhancements have been made regarding the materials used to improve their durability and performance, observes Bezold. “Furthermore, architectural improvements were implemented to increase the capacity of HEPA filters. Some recirculation filters are available with absorber stages to reduce the concentration of odorous substances in the recirculated air,” he says. “Airbus has always taken great care to enable a safe environment on board an aircraft — a commitment which remains unchanged and enhanced in a post-pandemic world. Our aircraft are designed and equipped by leveraging the latest technology for the most rigorous and absolute best in health, safety, and comfort. Strict compliance with the published maintenance procedures is key to maintain good air quality. This also applies to troubleshooting and decontamination in the case of a cabin air event.”
As to the maintenance that is needed on HEPA filters, Hartenstein affirms that such filters require periodic replacement on airplane for optimum performance, with adapted procedure for removals and disposal by the maintenance crew.
Automation
Environmental control systems are highly automated control systems, affirms Hartenstein. “The control algorithms are typically designed to adjust the energy drawn from the aircraft to the necessary levels to ensure safe and comfortable environment in the cabin, in terms on temperature, air changes in the occupied compartments, humidity, pressure, and rate of pressure variation in the cabin during the mission,” he says. “Human factors are clearly a key element in the design of the monitoring, indication, and crew/system interfaces. The system interfaces are inherently designed with human factors and crew operation specialists to prevent selection of inappropriate conditions for the cabin (e.g., temperature, pressure), and provide comprehensive reporting and indication of malfunctions should crew actions be required.”
A key objective of environmental control systems’ design is aiming at minimising crew workload while providing smooth controls and superior thermal comfort where automation is a key enabler, observes Bezold. “Human factors are an essential element in the design of environmental control systems because they need to be considered to design systems with low crew workload and to achieve a smooth and efficient operation of the ECS maintaining a comfortable environment for passengers and crew,” he says.
There is currently no information to pilots or cabin crew if there is something else that they need to worry about – e.g., chemical substance that has the potential to harm crew and passengers, or potential gradual lack of oxygen which could be hard to detect until it is too late, according to Teledyne. “We want to empower the crew and the airlines with enhanced cabin environmental systems that assist in making informed decisions sooner, through the use of rich data,” says Teledyne.
Reliability and Maintenance
The reliability figures of environmental control systems have improved over the years due to extensive analysis of in-service data and consequent improvements of affected equipment and system areas, according to Bezold. “Thanks to a huge aggregation of operational data Airbus gains a deeper insight into operational effects. Hence the design teams are in a position to permanently improve reliability and reduce maintenance efforts of the customer. This is based on smart algorithms for data analytics and predictive maintenance functions,” he says.
Environmental control systems are typically complex electromechanical systems, operating continuously, and submitted to very harsh environments- i.e., high temperature, pressure, and vibration levels, observes Hartenstein. “The reliability of the equipment, the ease of maintenance, and the operational reliability of the system are key and have been the subject of considerable design efforts for improvement over the years,” he says. “For example, the implementation of newer generation of systems with better controls, optimized architectures, and improved equipment, has demonstrated multiple in-service merits, and specifically an improvement of reliability of key equipment up to a factor two or three and a reduction by a factor two or three of aircraft operational interruption due to air systems, while at the same time offering optimized energy draw from the engine reducing by up to 20% fuel burn associated with environmental control systems.”
Enhanced Flight Vision Systems (EFVS) were certified for the first time in the early 2000s and from that moment they have been steadily expanding across both commercial and business aviation. What is the level of adoption of EFVS in industry? What are the benefits, enablers and inhibitors of EFVS, the human factors consideration that guide EFVS development, and the peculiarities of retrofitting? Read on to find out.
According to Dror Yahav, chief executive officer at Universal Avionics, over the years, EFVS has been adopted and made standard on many forward fit aircraft. “It has also been adopted by FedEx on most of its widebody aircraft. Elbit Systems and Universal Avionics alone have delivered over 3,000 Enhanced Vision System sensors since the early beginnings in 2001,” he said. “In retrofit, Universal Avionics’ ClearVision system is currently being certified on the King Air B200 and on the Boeing 737NG. Similar ClearVision systems from Universal Avionics are in advanced development for the rotorcraft market.” See sidebar page 24.
The Universal Avionics ClearVision system is a complete Enhanced Flight Vision System (EFVS) providing head-up capability combined with enhanced vision (EVS) and synthetic 3D terrain display (SVS) with a split screen display that allows the user to change between the two background imagery areas. Universal Avionics image
Indeed, EFVS is available on some commercial aircraft models. According to Grant Blythe, director of product marketing for Avionics at Collins Aerospace, until 2017, regulations did not allow airlines (Part 121 carriers) to conduct EFVS operations, limiting the market for these systems on commercial aircraft. “Since those regulations were updated, airlines have shown strong interest in this technology and we have been working quickly to bring these systems to market for commercial operators,” he said. “Collins Aerospace EFVS is available now for the Boeing 737 and will enter service on Airbus A320/A321 in 2025. We are looking forward to announcing additional aircraft soon.” See sidebar page 22.
For now, Airbus is developing EFVS on the A320 and the A350 families, said Maurice Garnier, avionics systems manager at Airbus. “This will include the A350 Freighter and the Airbus Corporate Jet Family. This EFVS capability may be deployed on other Airbus aircraft,” he said.
For what concerns business jet operators, EFVS operations have been allowed for much longer time, according to Blythe. “Subsequently, EFVS is widely available on mid-size and larger business jets. In fact, EFVS is often included as standard equipment on these higher end corporate jets.”
EFVS Benefits, Enablers and Inhibitors
According to Yahav, among the benefits of EFVS there is increased safety at night and during adverse weather conditions. “The ClearVision system is certified all the way to touchdown and rollout in reported visibility as low as 1,000’, making operating in almost any conditions possible. For Part 135 and Part 121 operators, the system also enables dispatch if the EFVS visibility is higher than 1,000’ at the arrival airport, increasing dispatch reliability,” he said. “This means the use of EFVS decreases delays and cancelled flights due to low visibility conditions. Coupled with a Head Wearable Display (HWD), the system allows safer flying in crowded airspaces by enabling pilots to operate Head-up during high workloads.”
Maurice Garnier Airbus
Indeed, a valuable combination of operational and safety benefits is provided by EFVS, according to Blythe. “Providing a night-vision-like capability, EFVS is particularly valuable in identifying runway incursions by wildlife or other aircraft, avoiding wrong-surface operations, or identifying terrain,” he said. “Operationally, EFVS can provide a very advanced all-weather operations capability at low cost for both airports and operators. For example, EFVS approaches can be performed today in visibility as low as 1000 feet RVR (Runway Visual Range) even at airports with limited ground infrastructure. This means better on-time performance resulting in happier passengers, lower operating costs, and reduced carbon emissions.”
Shown here, a pilot looking into a Head-Up-Display (HUD) which is used to display EFVS. Airbus says it is important that training be anticipated by customer operators of EFVS, as trajectory and energy symbology is key when flying with EFVS. Airbus image.
The main benefit provided by EFVS is situational awareness, said Garnier. “It provides the capability to see during the night and through different kinds of weather and low visibility conditions. Based on new regulations regarding all weather operations (AWO), EFVS will also bring operational benefits. The flight crew will be allowed to perform the flight toward the destination airport and attempt the approach in low visibility conditions using the EFVS in lieu of visual reference for the final part of the approach.”
Currently, advanced infrared and visible-light sensors are at the core of EFVS systems, according to Blythe. “These sensors can detect energy at very low levels and in spectrums outside the range of the human eye providing this enhanced visibility,” he said. “Of course, these sensors are still limited by physics. Today they are certified to provide a 33% visual improvement to natural visibility or ‘visual advantage’. With additional optimizations and possible integration of future technologies like millimetre-wave radar, Collins plans to further improve the effectiveness of these systems in the future.”
Garnier points out that since it is via the Head-Up-Display (HUD) that the EFVS delivers the information to the pilots, the main enabler is the HUD. “The HUD option already proposed by Airbus is based on a digital HUD with a video input capability. EFVS function will be fully integrated into Airbus operations and avionics architectures with dedicated controls, failure management and maintenance messages,” he said.
Human Factors Considerations
The goal of developing EFVS systems is to help pilots make better decisions and operate aircraft more precisely by presenting them with the best information available, according to Blythe. “Further, it is important we allow pilots to look through the EFVS system rather than simply look at it. Subsequently, we spend a great deal of effort removing any extra information from the display,” he said. “At higher altitudes before the EFVS can detect the approach and runway lighting pilots are looking for, our EFVS systems are tuned to not display static or blank fog only presenting pilots with useful information and detail.”
It is important that training be anticipated by customer operators, as trajectory and energy symbology is very important to fly with EFVS, observes Garnier. “The first step to this symbology is the ‘harmonized’ primary flight display (hPFD) that is available on all current Airbus Family aircraft. Pilots who are familiar with the hPFD symbology will be best able to take advantage of the EFVS,” he said. “There is no clear inhibitor identified but we consider that the main challenge will be ensuring the full integration of this new product in Airbus aircraft and avionics systems.”
According to Yahav, the human factors related to the management of symbology and information in the system to ensure a balance of important information are important to the EFVS design and development. “Cockpits are incredibly busy spaces, so ensuring that the information provided to the flight crew is relevant, helpful, and efficient is incredibly essential to maximizing performance and minimizing pilot fatigue,” he said.
With regard to EFVS, Airbus follows Human Factors considerations and precautions that are similar to the ones that already apply for any avionics development in Airbus Design Office. “Pilots and human factors experts are involved in the design that is continuously challenged through evaluations on simulators,” said Garnier.
Advantages and Disadvantages of EFVS Retrofitting
Various EFVS retrofit solutions are available directly from the OEMs, observes Yahav. “Universal Avionics, having made its name in the retrofit space, offers its ClearVision system for retrofit applications,” he said. “The ClearVision system is designed as in ideal forward fit or retrofit fit solution by leveraging Head Wearable Display (HWD) technology. This technology is considerably less intrusive to install as a retrofit solution than traditional HUDs and therefore minimizes aircraft downtime. Once installed, the system affords the same operational credits as a forward fit installation.”
The new Collins Aerospace EVS-3600 system, and its complementary HGS-6000 Dual Head-up Guidance System, will be available for retrofit on both 737 NG and 737 MAX models. The new EVS will also be available as a linefit option for new Boeing 737 MAX aircraft soon, Collins Aerospace says. Collins Aerospace image.
EFVS will be proposed for retrofit, and some system provisions will be proposed before EFVS certification in order to ease such retrofits, said Garnier. “The same EFVS product will be available for line-fit as for retrofit. EFVS retrofit will allow customers to update their in-service aircraft to the same level as their new delivered aircraft with EFVS function. They will both benefit from the same state-of-the-art EFVS system.”
Collins Aerospace offers EFVS solutions for both retrofit and linefit applications, affirms Blythe. “Retrofit EFVS gives our customers the flexibility to adopt new technologies like EFVS on the best timeline for their operations. It also allows them flexibility to update aircraft when they might acquire or lease used aircraft without EFVS,” he said. “Retrofit installations sometimes have additional challenges in completing wiring and mechanical work and need to account for the opportunity cost of aircraft downtime but we offer turnkey retrofit packages and on-site installation support to make these installations simple and straightforward for our customers.”
Some aircraft downtime is be entailed by retrofit embodiment / working party access to the aircraft, depending on the configuration. “The closer that an aircraft is to the full EFVS configuration then the shorter that downtime. We recommend customers who are interested in EFVS to implement the HUD option on their aircraft and EFVS full provisions as soon as they are available,” concluded Garnier.
Avionics software testing ensures that avionics technology delivers its intended functions and that it does so safely and securely. What do industry experts consider best practices in the domain of avionics software testing? What are the standards of reference and the qualifications of those conducting the tests? And what are the current and coming testing developments? Here’s what the experts had to say.
Early and Often
One key question about avionics software testing is how often it should be conducted. There are several aspects to consider, according to Ricardo Camacho, director of safety and security compliance at Parasoft. “It is important that testing be performed as early and often as possible. For example, during requirements decomposition and architectural design, many organizations have adopted modeling because the complexity is so great that the need to abstract from text to pictures is required,” he said. “SysML or UML is the modeling language of choice. It gives the system engineer the ability to build a logical architecture, test it through simulation, further refine the design, and follow it with a physical architecture that can also be tested before handing it over to software development.”
Ricardo Camacho, Parasoft
While early testing of avionics software applications is usually performed in a simulated environment, i.e. “on-host testing,” DO-178C guidance requires the testing of software applications on the final hardware on which they will be hosted, said Nick Bowles, head of marketing at Rapita Systems. “This type of testing is known as ‘on-target’ testing and usually happens further along in the software development lifecycle (SDLC). On-target testing provides vital evidence that the software will perform as expected when hosted on the real avionics platform it is designed for.”
Nick Bowles, Rapita
Across the industry, there are multiple avionics software testing techniques in use, Bowles noted. “While informal testing can take place, formal tests that count towards the certification of avionics software (such as DO-178C guidelines) should map directly to specific software requirements that are defined before software development begins,” he said. “To achieve higher-level testing, more of the final production software needs to be integrated together, so lower-level testing is possible earlier in the SDLC.”
To ensure that a sound system is built, it’s necessary to use a model execution or simulation to test the architecture and interfaces between the system’s parts, according to Camacho. “Testing will be performed again and again as the system evolves to the point that it is handed over to the software team for implementation,” he said. “In addition, system engineers define test cases on what and how the system should be tested for the quality assurance team to realize the test cases and perform the testing.”
The “early and often” principle of avionics software testing changes when the software team determines a solid and deliverable codebase and hands it over to the quality assurance team, Camacho said. “As an independent third party, the QA team exercises the code and system to flush out any unidentified bugs or functional flaws. Compliance to standards like DO-178C and others is also often required. A lot of work goes into this, and it can take a QA team many months to achieve.”
Standard of Reference
Indeed, DO-178C (ED-12C in Europe) is the primary document that provides guidance for developing airborne software systems. “DO-178 was developed in the 1970s and defined a prescriptive set of design assurance processes for use in airborne software development focused on testing and documentation,” Bowles said. “In the 1980s, DO-178A was released, which introduced the concept of different software criticality levels and prescribed different activities for different levels. Released in 2012, DO-178C clarified details and removed inconsistencies from DO-178B. DO-178C also includes supplements that provide specific guidance for design assurance when specific technologies are used.”
Benjamin Brosgol, AdaCore
The DO-178C standard for airborne software places a strong emphasis on verification in general and on testing in particular, according to Benjamin Brosgol, senior software engineer at AdaCore and vice chair of The Open Group FACE Consortium’s Technical Working Group. “The standard’s approach to testing has an important distinguishing characteristic: In contrast to so-called ‘white-box’ testing, in which test cases are derived from the source code’s control structure, DO-178C specifies that testing is always based directly on the software’s requirements,” he said. “Additionally, the major change from DO-178B was not so much in the ‘core’ document but rather the formulation of specialized supplements on model-based development and verification, object-oriented technology and related techniques, and formal methods. Using any of these technologies affects the nature and extent of the requirements for testing.”
Regarding where avionics software test automation is headed, Camacho believes that the incorporation of artificial intelligence and machine learning will bring about transformations that were not previously considered. “Just as new requirements to address security concerns have been developed, I believe that new requirements around autonomous avionic systems, particularly in civil aviation, is where we will see new standards arise,” he said.
According to Brosgol, a current industry trend is the increasing emphasis on cybersecurity, and this trend can affect testing in several ways. “One is the growing usage of ‘fuzzing’ as a technique for detecting vulnerabilities.
Another is the adoption of sophisticated static analysis techniques, including formal methods, to supplement testing and to prove security-based program properties such as correct information flows,” he said.
Conducting the Tests
There is no official accreditation for performing avionics software testing, and this means that potentially anyone can do so, Bowles pointed out. “However, there are certain qualities and skills that are important to be a good avionics software tester or ‘verification engineer’ as this figure is sometimes known. A background in software or system engineering is advantageous, as understanding how a system is developed is key in being able to effectively test it,” he said. “Furthermore, some software tests might need to be written in scripting languages that require programming knowledge.”
Typically, software engineers who perform software development and software engineers who become part of the QA team are allowed to conduct avionics software testing, Camacho said. “They are ‘allowed’ because they have the software background to develop software test cases needed to verify and validate avionic systems. There is no particular training required, except being a software engineer. The only type of training required for software engineers will be on the tools that help automate and perform testing.”
To help ensure that all the test cases needed have been created, C/C++test can perform code coverage, which highlights the code that has been exercised during testing, Camacho said. “Code that is unexecuted means that there is no test case that addresses that code. There are other software tools that compile and build test code, archive test files, execute test scripts that automate testing, capture test results, and produce test reports for proof of compliance and auditing purposes. So, just to reiterate, software engineers have the necessary education and background to be allowed to conduct avionics software testing.”
Current and Coming Developments
In the evolution of testing, the drivers have been safety and security. “This appears to be further expanding into multiple condition coverage (MCC), which is more thorough than modified condition decision coverage (MC/DC) and requires a much greater number of test cases — two to the power of the number of conditions in the code statement,” said Camacho. “MCC is not officially mandated, but it’s another level of safety that could be adopted in the future.”
Security boils down to securing the data, and that data exists in different forms at various levels of abstraction within the scope of the aircraft and avionics systems, Camacho explained. “Since these avionic systems are connected, one must secure them at every entry and exit point, including down to the subsystems and units of software that exist. Data at all these levels needs to be secure,” he said. “Testing to ensure that the data is secure is done through various test methods. Some of these include security scanning with coding standards like CERT, unit testing, system testing, fuzz testing, penetration testing, brute force attacks, and checking ingress and egress points for unauthorized networks.”
The software security objectives that avionics software testing also has to satisfy include the ones described in DO-326A and ED-202A, titled “Airworthiness Security Process,” said Paul Butcher, senior software engineer and AdaCore’s lead engineer in the UK for HICLASS. “These publications, and their supporting guidelines DO-356A and ED-203A, describe testing methodologies that differ from standard verification testing and instead introduce the term ‘refutation.’ The goal behind refutation testing is to plan a test strategy that aims to refute a claim that the system is not secure. More specifically, we utilize refutation testing techniques to measure security assurance by purposefully adopting the mindset of an attacker and trying to identify and show the exploitation of any application vulnerabilities.”
There are two distinct categories in security refutation testing techniques: dynamic and static, Butcher explained. “Static analysis techniques, including source code analyzers and formal verification, aim to identify potential run-time and logic errors prior to code execution. Dynamic analysis techniques, including constraint checking run-time environments and negative testing techniques such as fuzz testing, are exercised as the application is executing,” he said. “One way to consider the difference is to think of static analysis as the act of identifying known categories of vulnerabilities within the application, whilst dynamic analysis is more about finding unknown categories of vulnerabilities. Both techniques are complementary to each other, and the recommendation is to adopt a layered approach where multiple testing methodologies are used to argue security, and therefore safety, assurance.”
Presently, one of the biggest challenges facing the industry is the testing and certification of avionics software designed for use on multicore platforms, observed Bowles. “The adoption of multicore processors in the avionics industry is growing due to their improved SWaP characteristics and the long-term supply chain issues of sourcing single-core processors,” he said. “However, the use of multicore processors for safety-critical avionics applications presents a range of challenges due to their nondeterministic behavior. Guidance addressing the testing of multicore avionics software applications has been incorporated into DO-178C (ED-12C) via EASA’s recent A(M)C 20-193 document, with the FAA’s AC 20-193 version expected to be released shortly.”
Things are headed in the direction of incorporating artificial intelligence and machine learning as part of avionics software testing, according to Camacho. “Testing is expensive for software avionics, so the next horizon in cutting cost, labor, and time needs to include artificial intelligence and machine learning. Testing where humans are involved is also error-prone, and these errors could be expensive. If artificial intelligence could analyze code and automatically determine how to test the code to ensure high-quality, safe, and secure avionic systems, that would be a dream come true for all industries developing software,” he said.
In the domain of air traffic management (ATM), communication, navigation, and surveillance (CNS) infrastructure is the foundation for the provision of air navigation services. As technology evolves, so must resilience, interoperability and the inclusion of new entrants. In this second part of our story on the evolution of CNS technology, we’ll review the resilience of the CNS system, civil-military interoperability, and the progress for the inclusion of unmanned and suborbital operations as new entrants.
In the domain of air traffic management (ATM), communication, navigation, and surveillance (CNS) infrastructure is the foundation for the provision of air navigation services. As technology evolves, so must resilience, interoperability and the inclusion of new entrants. In this second part of our story on the evolution of CNS technology, we’ll review the resilience of the CNS system, civil-military interoperability, and the progress for the inclusion of unmanned and suborbital operations as new entrants.
Developing Resilience
In ATM, resilience is the intrinsic ability of a system to adjust its functioning prior to, during, or following changes and disturbances, so that it can handle required operations under both expected and unexpected conditions, according to Ruben Flohr, an expert on ATM architecture and systems engineering at SESAR Joint Undertaking in Brussels. “This means that the CNS systems need to keep functioning to an acceptable level, irrespective of atmospheric weather, space weather, cyberattacks, system component failures, etc.,” he says.
Ruben Flohr, SESAR JU
According to the Civil Air Navigation Services Organization, CNS resilience can be considered as an interconnected set of redundancies. “The industry has worked diligently to remove ‘single points of failure’ and the air traffic management system is continually monitored to detect anomalies,” says Coleen Hawrysko, CANSO’s operations program manager.
Coleen Hawrysko, CANSO
Resilience can be developed in two main ways. “Within a system, the components can be made redundant, so that there is no longer a single point of failure. An example is the voice communication systems for an air navigation service provider (ANSP), which are usually installed with triple redundancy through systems of different providers. Another example is the redundancy of power sources at an ANSP, allowing seamless switching between the public electricity net, local diesel generators as backup, and batteries as last resort,” says Flohr. “Another way to increase resilience is to make multiple technologically different solutions available for the same function. An example of this is the VOR/DME (or LDACS: L-band Digital Aeronautical Communications System, in the future) that can serve as A-PNT (Assured Positioning, Navigation and Timing) to mitigate for any outages of GNSS (Global Navigation Satellite System). In the example of datalink, the introduction of the multilink concept enables a seamless switch between all available channels. Depending on where the aircraft is, this could be AeroMACS (Aeronautical Mobile Airport Communication System), LDACS, VLDM2 (VHF Datalink Mode 2) and/or SATCOM, mitigating the risk of temporary failure of any of the individual links. In the example of GNSS, resilience is also increased by introducing the usage of multiple satellite constellations and multiple frequencies within each constellation. This mitigates any potential temporary failure of a single constellation like GPS and may also mitigate aviation collateral damage from road traffic-related targeted single frequency GPS jamming.”
Ghislain Nicolle, vice president of Air Traffic Services at Inmarsat, says the CNS infrastructure is extremely resilient and robust, and in order to provide a safety service, resilience is built in by design. “Nevertheless, as communications between aircraft and ground systems are increasing, creating more and more dependencies on those transmissions, we need to look at resilience in a more systemic way. This involves taking advantage of every available link in the communication capabilities rather than looking at individual capabilities separately,” he says. “This is what we call the multilink approach, which ultimately will enable CNS/ATM to be performed in a fully integrated manner, taking advantage of all radio links available on board.”
A CNS advisory group under the lead of the European Commission is currently exploring ways to translate the principles of resilience into a CNS evolution plan to be consistent with the ICAO Global Air Navigation Plan and the CNS roadmap of the ATM Master Plan, says Christine Berg, head of the European Commission’s Single European Sky Unit at the Directorate General for Mobility and Transport. “It should cover the short, medium and long-term evolution of the CNS infrastructure in Europe and the related transition phases to reach full implementation, enabling the synchronized implementation of airborne elements, ground capabilities and the development of space-based technologies,” she says.
Civil-Military Interoperability
The CNS advisory group is assessing how CNS infrastructure improvements should be effectively managed by identifying lessons learned, key drivers, actions and decision points that will be necessary to support the European ATM Master Plan operational objectives, says Flohr. “Furthermore, the group is in the process of identifying the issues for which EU regulatory or policy actions may be required. It is important to ensure a synchronized deployment of ground stations and avionics, the reason being that the benefits only appear once all components of such a system are deployed,” he says. “A synchronized deployment, however, is not that straightforward, as the different components need to be deployed and paid by different stakeholders, each of them requiring a positive business case for their own expenses. Another challenge is to minimize the use of exemptions from commonly agreed standards. This is, for example, relevant for state aircraft. That is why the civil-military cooperation and interoperability is within the scope of this CNS advisory group.”
Christine Berg, European Commission
Nicolle observes that in civil airspace, military aircraft are using the same CNS/ATM systems as any commercial aircraft and are subject to exactly the same rules. “They are therefore fully integrated in the CNS/ATM system. From an Inmarsat perspective, we make a point at making sure that our terminals fitted in military aircraft operate in accordance with the standards set forth by ICAO, which prevails over the civil airspace,” he says.
Inmarsat recently launched its Velaris UAV connectivity solution. The company says it will deliver new digital automation capabilities, allowing operators to send their drones on long-distance flights and to access various applications, such as real-time monitoring, to ensure safe integration with other air traffic. Image by Rainer Puster.
Civil and military airspace users have very different operational, technical, and business needs, yet use common CNS services and infrastructure, Berg points out. “This is why all stakeholders would need to be involved in the development and endorsement of a common evolution plan addressing civil and military perspectives. The European ATM Master Plan already contains a CNS roadmap, endorsed by civil and military stakeholders, defining the targeted CNS infrastructure over the next decade without entering into detail. A joint effort to define a CNS evolution plan, also involving Member States, would help to improve mutual trust and understanding,” she says. “An inclusive decision-making process is important to reconcile potentially contradictory requirements and cases where the evolution may impact stakeholders differently. Member States should try to harmonize national military requirements and plans related to CNS wherever possible to contribute to a European evolution plan covering both civil and military needs. Civil-military cooperation has strong potential to support a rationalized and resilient CNS infrastructure: data sharing will improve performance and assist in the rationalization of surveillance systems, in particular. A robust data-sharing network with relevant cyber-protection and cyber-resilience is essential.”
Unmanned Traffic
Unmanned traffic management (UTM) is the next frontier, according to Nicolle.
“UTM will be similar to military aviation, in that they will have to comply with civil aviation rules and integrate into the civil airspace. The main difference is in terms of numbers, as we are talking about much higher volumes of airborne data and equipment, for which artificial intelligence will play a major role,” he says. “This is what Inmarsat is preparing with its Velaris program. It is clear that commercial UAVs will have a positive and far-reaching impact on various aspects of society and business, ranging from cargo delivery, urban transport and surveillance to emergency services and disaster relief. However, unless autonomous vehicles and unmanned aviation are safely and securely integrated into managed commercial airspace, their true potential cannot be unlocked on a commercial scale.”
Inmarsat’s recently launched Velaris UAV connectivity solution will deliver new digital automation capabilities, allowing operators to send their drones on long-distance flights and to access various applications, such as real-time monitoring, to ensure safe integration with other air traffic, notes Nicolle. “In addition, Velaris will allow a single pilot to remotely operate multiple UAVs at scale, making operations more commercially viable and supporting the transport of people and goods in an environmentally friendly manner,” he says.
The European initiative to develop an ecosystem for the safe and secure integration of UAS is still under development. “Requirements for CNS in support of tactical separation will depend on the operational concept to separate UAS. Such requirements are not yet defined, and research is ongoing in SESAR, in particular in relation to the surveillance of UAS,” says Flohr. “As drones are operated by remote pilots on the ground, this is unlikely to have much impact on the A/G communication from UAS to ground-based UAS separation management (ATC or U-space management), with the exception of the command & control (C2) link from the operator to the drone/UAS. However, for drones this is currently not planned to be run over the aviation safety critical spectrum, which remains reserved for manned aviation. IFR traffic of remotely piloted aircraft systems (RPAS) into regular ATC is expected to follow all the CNS principles like any manned aircraft flying in controlled airspace.”
Suborbital Operations
Suborbital operations are another future entrant, and they are likely to be very different from regular air traffic. “In particular, this is due to the fact that the possibilities for tactical control are very limited at such altitudes,” says Flohr. “The type of separation control is expected to be much more based on pre-tactical or even strategic separation, and hence will have very different performance requirements on the corresponding CNS functions. An operational concept for this is not yet defined.”
One emerging challenge with both UAVs and suborbital operations is the vertical separation of these new entrants from the regular air traffic, according to Flohr. “In the near future, SESAR intends to investigate the transition from barometric to geometric [altitude measurements], considering that positioning for the UAS is heavily reliant on GNSS, and only the more sophisticated drones that are prepared for IFR integration are being equipped with barometric sensors. The SESAR research project ICARUS is looking into this for UAS,” he says. “The suborbital operations are at such a high altitude that the gradient of barometric pressure becomes too low to distinguish flight levels with the same accuracy as for regular air traffic. In order to avoid losing space by adding huge vertical buffers between traffic, it would be much more efficient to separate them by using geometric altitude, which is GNSS-based.”
CANSO has its own workgroups and task forces focused on resolving the issues of interoperability and the inclusion of new entrants, and it is also involved in many global workgroups. “CANSO also recently established the Complete Air Traffic System Council, an innovation forum composed of leaders from across the entire aviation industry (both manned and unmanned) to design a blueprint for future skies,” says Hawrysko.
“The implementation of the operational changes defined in the 2020 edition of the European ATM Master Plan can drive the evolution of CNS infrastructure, including the provision of services to new entrants (e.g. U-space services) and for higher airspace operations,” Berg says.
In part one of our look at the status of CNS/ATM modernization efforts, Mario Pierobon explores the evolution of the diverse components that come together to make flying safer, more efficient and less impactful to the environment and to learn about what is coming next.
In the domain of air traffic management (ATM), communication, navigation, and surveillance (CNS) infrastructure provides the foundation for the provision of air navigation services. CNS infrastructure includes various on-board, ground-based, and space-based components, that are subject to technological evolution, very much like the whole ATM concept is subject to evolution. In this first part of a multi-part story on CNS technology we shall concentrate on how the traditional CNS infrastructure has developed since the early days, where the technology is headed, and the main drivers of the changes in CNS technology.
ATM Modernization
Indeed, CNS infrastructure has developed significantly since the early days of aviation. “For oceanic flights, we have moved from CNS being driven by flight engineers who would perform navigation manually using paper charts and report the position of the aircraft through voice contact with high frequency radios, to augmented GPS systems built into aircraft automatically reporting their position and routes using satellite communications. This digitalization has taken 20 years to develop to a point that it is now mandated across the most important routes around the globe.” says Ghislain Nicolle, vice president of air traffic services at Inmarsat.
CNS systems enable airspace capacity and efficiency, and they can also contribute to environmental sustainability.
According to Christine Berg, head of the Single European Sky Unit at the Directorate General for Mobility and Transport of European Commission, the various CNS systems enable airspace capacity and efficiency, and they can also contribute to environmental sustainability. “We should keep in mind that the CNS infrastructure does not deliver operational benefits directly; it is a technical enabler for providing operational benefits to ATM and airspace users,” she says. “CNS infrastructure, including both deployment of new CNS systems and rationalization of some legacy CNS systems, must evolve to achieve the long-term objective of ATM modernization — the Digital European Sky — as defined in the European ATM Master Plan in our case.”
Christine Berg, European Commission
In practical terms, the evolution of CNS systems means that there will be progressively more integrated, secure and performance-based CNS services making use of more satellite-based solutions, as well as an improved exchange of information between aircraft and the ground, according to Berg. “A unique opportunity has emerged, because of the economic impact of the COVID-19 crisis, to accelerate the rationalization of CNS infrastructure, benefitting from the decisions of some airlines to no longer operate certain aircraft types,” she points out.
In the context of the Single European Sky (SES) regulatory framework, CNS infrastructure should be managed, modernized, and operated to support the achievement of Union-wide performance, in terms of reduced environmental impact, cost-efficiency, network capacity and safety for all citizens,” according to Berg. It should enable the implementation of cross-border and pan-European service delivery models, and respect security and defence requirements,” she says.
Inmarsat is currently working in partnership with the European Space Agency (ESA) on the Iris program to develop a solution of air traffic management over the continental airspace, points out Nicolle. “Iris will deliver new communications capabilities enabling both enhanced air traffic services as well as better communications with the airline’s operation center,” he says. “This will not only improve airspace usage to accommodate future growth but will also allow airlines to fly shorter and more efficient routes, minimize flights delays, save fuel and reduce the carbon footprint of their operations. It really is a great example of the vast benefits the new area of digitized aviation can bring to aviation travel.”
Evolution of Communication Technology
Historically, the need to improve CNS emerged as a result of congested skies, expanding aircraft operations and airspace security concerns, observes Coleen Hawrysko, CANSO’s Operations Program manager. “From the advent of two-way radio communications and radio navigation beacon systems in the first part of the 20th century, pilots now communicate with air traffic control and their operation centres utilizing any of several systems – very high frequency (VHF), ultra-high frequency (UHF), and high frequency (HF) voice communications, as well as digital communications utilizing data link and satellite voice,” says Hawrysko.
Coleen Hawrysko, CANSO
The transition from voice to digital message had already begun with the introduction of controller pilot datalink communication (CPDLC), emphasizes Ruben Flohr, expert in ATM architecture and systems engineering at SESAR Joint Undertaking. “In the long term, a further shift is expected that will enable the transformation from single voice-based ATC instructions to trajectory-based operations (TBO) that build on closed-loop control whereby a ‘complex’ clearance is uplinked over datalink composed of geo-positions, time, altitude, speed and heading instructions,” he says. “The updated flight path, incorporating the complex clearance, is then downlinked through the extended projected profile (EPP) to confirm to the air traffic controller (ATCO) that the flight management system (FMS) has accepted the complex clearance. This will increase the predictability of the flight’s trajectory both for the pilot and the ATCO, and hence enable more fuel and climate efficient conflict avoidance.”
CNS infrastructure has developed significantly in the past 20 years. This roadmap for the backbone infrastruction shows where the future lies. Image courtesy of the European ATM Master Plan (2020 edition)/Copyright: SESAR Joint Undertaking.
Ruben Flohr, SESAR JU
Drive Towards GNSS
In the very early days of aviation, a pilot navigated by looking out of the cockpit window, following a coastline, a river, roads and recognizing landmarks like lighthouses and church towers, observes Flohr. “The early navigation from the outside view only, was clearly fully dependent on visibility, and to mitigate this dependency, beacons were installed. Different technologies arose, like the VHF omnidirectional radio range (VOR) to enable the aircraft to measure its angle from such a beacon, and the distance measuring equipment (DME) to enable the aircraft to measure its distance from such a beacon. On-board systems would combine multiple beacons to determine the aircraft position. Complementary to the beacons, the inertial navigation system (INS) was introduced,” he says.
Since the 1980s a new mode of navigation became available which was based on a position signal from space: the global positioning system (GPS) provided by the United States. “GPS was the first example of a Global Navigation Satellite System (GNSS), and it was later complemented by other satellite constellation systems, launched by Europe (GALILEO), Russia (GLONASS), and China (BEIDOU),” says Flohr. “Up until now, most western GNSS-based air traffic navigation systems have been solely based on GPS. SESAR research is ongoing to also integrate the other constellations for navigation, either as crosscheck or as fallback to increase reliability and integrity, and hence increasing safety levels.”
CNS technology contributes to the safe operation of flights, as well as a significant impact efficiency while supporting the growth of air travel.
Technological Upgrade of Surveillance
From ‘line of sight’ and manual position reporting to the development of radio detection and ranging (RADAR) developed post-World War I and other terrestrial based systems, surveillance systems have evolved now to the provision of enhanced surveillance utilizing satellite technologies, observes Hawrysko. “Due to increasing costs involving maintenance and sustainability, many legacy RADAR systems are being decommissioned in favour of automatic dependent surveillance – broadcast, or ADS-B. As technology rapidly evolves, enhanced voice communications utilizing satellites is also on the near horizon,” says Hawrysko.
Indeed, the shift towards space-based ADS-B is ongoing, and already operational in some oceanic regions, affirms Flohr. “As far as terrestrial surveillance is concerned, there is still debate about the safety case related to completely trading primary radar for secondary dependent surveillance only,” he says. “In particular, in the light of resilience the need for back-up solutions is still relevant, for example jamming of the GNSS signal in regions of war is quite common.”
Drivers of Change
According to Nicolle, CNS technology is not only needed for the safe operation of the flight, but it can also have a truly significant impact to fly aircraft more efficiently while supporting the growth of air travel. “CNS technology allows airlines to offer better routes by, e.g., taking advantage of tailwinds to reduce flight time – offering a more comfortable flight for the passenger, while at the same time supporting the growth of capacity of the overall system as needed over the busiest routes,” he says.
The most important driver to change in CNS technology is to support future operational concepts, according to Flohr. “Some of these concepts, along with the expected traffic growth, require improved technical performance levels (in terms of latency, data capacity, accuracy, etc.) that the current CNS technologies are not able to meet,” he says. “Another overall trend is the transition from a technology-based to a performance-based CNS framework, in which the technical performance indicators for CNS systems (e.g., availability, integrity, and continuity) are defined for specific operational needs and types of airspace, without any system pr technology prescription.”
The ultimate goal is to offer the most possible flexible routing capabilities without compromising on the safety of flights, according to Nicolle. “This is what we are currently seeing over the North Atlantic airspace with the deployment of the oceanic track system (OTS). For busiest airspaces such as Europe and China which are rapidly becoming saturated in certain areas, there is a higher demand for satellite communications which Iris is going to fulfil to allow for effective and secured voice and data communications,” he says.
The ultimate goal of upgrading CNS is to offer the most flexible routing capabilities without compromising the safety of flights.
Airspace safety and efficiency have always been important to CNS technology enhancements, affirms Hawrysko. “As airspace becomes increasingly congested, the need for immediate air traffic control/pilot communications has never been greater. Navigational and surveillance accuracy are key contributors to a safe and efficient air traffic management. Our industry is working diligently to improve voice communication capabilities in remote and deep ocean airspace,” says Hawrysko.
Berg believes there is a set of main guiding principles that should be considered when changing CNS technologies. “First of all, change must be driven by the needs of civil and military stakeholders, including those of new entrants, e.g., drones. The services provided by CNS systems must ensure safe and secure operations and the evolution of CNS technologies must follow an integrated (iCNS) and primarily a performance-based approach,” she says. “In addition, airborne, ground and space components must be interoperable, including at global level; this also means compliance with ICAO standards and coordination with relevant international partners. CNS systems must be able to use spectrum more efficiently and the provision of iCNS services should shift from local to cross-border and pan-European CNS operated infrastructure. Ultimately such transition should foster not only the modernization but also the rationalization and decommissioning of legacy civil CNS infrastructure.”
Summing Up
The modernization of the ATM system is an ongoing effort, and it includes the technological upgrade of CNS infrastructure in a performance-based mode. The second part of this multi-part story will concentrate on the resilience aspects of CNS infrastructure, its interoperability, and the inclusion of new entrants in the airspace.
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