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SENSors and certifiable hybrid architectures FOR safer aviation in ICing Environment

Periodic Reporting for period 2 - SENS4ICE (SENSors and certifiable hybrid architectures FOR safer aviation in ICing Environment)

Reporting period: 2020-07-01 to 2021-12-31

Modern airplanes are well equipped to cope with the most common icing conditions, which are defined Appendix C of FAR Part 25 / CS-25. However, some conditions containing Supercooled Large Droplets (SLD) have been the cause of severe accidents over the last three decades. It has become clear that improving safety is of high importance for these icing conditions as ice can form on unprotected areas of the lifting surfaces. Consequently, authorities addressed these safety concerns by issuing new certification rules under Appendix O of FAR Part 25 / CS-25 to ensure that future airplanes remain controllable in these conditions and can exit safely upon detection. Hence, the key to increasing overall aviation icing safety is the early and reliable detection of icing conditions to allow the necessary actions to be taken by the flight crew. The EU-funded project SENS4ICE (SENSors and certifiable hybrid architectures for safer aviation in ICing Environment) directly addresses this need for reliable detection and discrimination of icing conditions.
Although much progress has been made on icing detection, there are considerable gaps which still exist, specifically regarding the newly introduced icing conditions of Appendix O. This is the focus of the novel approach of the SENS4ICE project which seeks to intelligently cope with the complex problem of ice detection through the hybridisation of different detection techniques. In the proposed hybrid system, the direct sensing of atmospheric conditions and/or ice accretion on the airframe is combined with an indirect detection of ice accretion on the airframe by monitoring the change of aircraft’s characteristics. SENS4ICE will address the development, test, validation, and maturation of the different detection principles, the hybridisation - in close cooperation with regulators to develop acceptable means of compliance - and the final airborne demonstration of technology capabilities in relevant natural icing conditions.
The first part of the project was devoted to the development and maturation of icing detection technologies, with a focus on Appendix O icing conditions. Furthermore, several icing wind tunnel facilities improved capabilities to represent Appendix O conditions. Icing wind tunnel testing (including Appendix O) of several icing detection sensors developed in SENS4ICE concluded the first part of the project. The main goal of the remainder of the project is flight testing of icing technologies in natural icing conditions including Appendix O.
As no standardised procedure exists for icing wind tunnels to generate and detect Appendix O icing conditions, extending icing wind tunnel capabilities towards the Appendix O icing regime resulted in valuable insights and gaining understanding. This includes measurements with reference instruments conducted in different icing wind tunnels and comparison and consistency analysis for relevant icing parameters.
Ten different technologies with various physical principles for directly detecting ice accretion or atmospheric icing conditions were developed and matured with the EU funding, of which one technology is for airborne scientific and reference measurements and nine are aiming at applications for operational air transport application.
Eight technologies provided testing results in different icing wind tunnels in Appendix C and O conditions. A standardised testing procedure and partly common test points between the different icing wind tunnels serve for adequate comparability of the results. Most sensor technologies were able to demonstrate the detection of a large portion of the Appendix O test points while at the same time ensuring very good detection capabilities for Appendix C conditions. Furthermore, some sensors are capable of providing specific relevant icing parameters like liquid water content and median volume diameter, which is considered as very beneficial as input for the hybrid ice detection system. The hybrid ice detection system was specified and initial considerations of certification aspects were developed in close cooperation with aviation certification authorities, aircraft manufacturers, pilot representatives and research institutions. Subsequently a suitable hardware and software architecture was developed in order to be flight tested. As part of the hybrid approach, a performance-based indirect ice detection system is developed and matured, able to early detect even relatively light ice accretion on the airframe by utilising fundamental knowledge about the changes of aircraft characteristics under icing conditions. Extensive analysis was conducted with flight test data to identify applicable thresholds for specific aerodynamic aircraft parameters. Preliminary results based on the existing data from flights in natural icing conditions (App. C icing conditions) show that a fast and reliable detection behaviour could be achieved. It is expected that this behaviour will be somewhat similar for flights in App. O conditions.
First flight tests have already been conducted and provided extensive characterisation of various different icing conditions. Further flight tests are planned for 2023 to test and demonstrate eight of the direct ice detection technologies under development and in addition the hybrid ice detection system including the indirect ice detection system. Extensive meteorological and climatological analysis is underway in order to have the best chances to encounter icing conditions including Appendix O conditions.
Furthermore, remote icing detection technologies were investigated, based on satellite data or airborne weather radar data. Both approaches show promising results and strengths weaknesses were identified.
The SENS4ICE consortium unites European and non-European aircraft manufacturers, equipment suppliers and research/academia with a large variety of technologies that have emerged in recent years, the most promising and mature of which have been selected for flight testing, while several other less mature but promising technologies are advanced in laboratory environment. Since icing is a global hazard, SENS4ICE will address this challenge with a global consortium including participants from Brazil, USA, Canada, and Russia. By aligning the EU funded activity with nationally and internally funded programs of those countries, a harmonized global view on Acceptable Means of Compliance can be achieved, and technological progress can be further advanced by ensuring complementarity and avoiding overlap.
The expected impact of the project is aiming to contribute to the key societal challenges of smart, green and integrated transport, considering the challenges of its competitiveness, performance and sustainability. SENS4ICE is tackling these challenges by contributing to increased passenger safety, decreased cost by improving certification rules, and increasing aviation efficiency by avoidance of icing hazards and lowering inspection and MRO operations.
Logo of the SENS4ICE project