The FAA release of 14 CFR Part 25 Appendix O and 14 CFR Part 33 Appendix D regulations for SLD and ice crystals has spawned an increased need for detecting and differentiating these icing conditions from the traditional Appendix C clouds. In order to perform these functions, changes to the measurement technologies and flight crew identification methods are needed. To assist ice detector and aircraft manufacturers in the design and certification of systems with these expanded functionalities, an update to ED-103 (AS5498) was recently released. Revision A of this document now provides requirements for the detection and differentiation of Appendix C, O, and D clouds.
With the increased reliance on ice detection systems over the last 25 years come increased expectations of performance verification through icing wind tunnel tests, icing flight tests and comparison to reference instrumentation to show compliance with FAA and AS5498A requirements. Demonstrating compliance to these detection and differentiation requirements over the wide variety of icing conditions presents a significant challenge – particularly as particle sizes increase and water content decreases. It has often been assumed that an ice detection system failing to meet all expectations would be certified as Advisory, giving the flight crew the primary responsibility for detecting icing conditions. This strategy, however, is not clear cut and has its own issues. The discussion herein is intended to shed some light on the certification challenges that exist for verifying the means to detect / differentiate all types of clouds and offers some suggestions on how to resolve this conundrum.
Darren Glenn Jackson
International Conference on Icing of Aircraft, Engines, and Structures