Infrared Spectroscopic Cloud Water Phase Determination in Icing Conditions

The icing of aircraft components is a fundamental issue in ensuring aviation safety and is therefore a central topic in the certification process of aircraft. To ensure the operability of aircraft and their components, regulatory authorities (EASA - Certification Specifications and FAA - Code of Federal Regulations 14) require proof of compliance with several provisions in different icing conditions (e.g. EASA CS-25, Appendices C / O / P, and CS-E). Incidents led to the recent addition of further icing conditions into the legislation, that are critical for safe flight operations. These include so-called supercooled-large-droplet (SLD), mixed-phase (mixed liquid and frozen water constituents) and ice-crystal-icing environments (high content of ice crystals). The reliable experimental replication of these conditions in the currently internationally available icing test infrastructure is only possible to a limited extent. For the future this will be indispensable in the development and certification process of aircraft components and deicing technologies, as well as in the validation of numerical simulation tools for aviation industries. Due to the lack of suitable measurement technology for the fraction of liquid water droplets and ice particles in the total (liquid and ice) water content, the requirements of these certification criteria are difficult to meet.

This is the need the exploratory project "AquaPhase" will address. It aims at elaborating, evaluating and subsequently establishing a practicable method for water phase discrimination i.e. the discriminating between water droplets and ice particles or snow, for icing research and development based on infrared spectroscopic technologies. The project involves the design of a measurement system and the experimental validation of the technology, which should enable a reliable measurement of the phase components in icing environments without the disadvantages of a complex optical measurement of the particle morphology. Subsequently, a potentially automated measurement system for icing infrastructure operators and the aviation industry for testing and certification purposes is drafted and the technical and economic potential will be analyzed and evaluated as a foundation for future R&D projects.