Flight in Icing Regulatory Evolution and the Influence on Aircraft Design

Flight in icing for transport category aircraft certification presents a particularly challenging set of considerations to establish adequate safety commensurate with the associated risk while balancing design complexity and efficiency. A review highlighting important aspects of the regulatory evolution and guiding principles for flight in icing certification is presented, including the current standards and recent rulemaking activity. While historical icing certification relied on a simple yet subjective requirement to demonstrate that an aircraft is capable of operating safely within the prescribed icing envelopes, the certification requirements associated with demonstrating an adequate level of safety have progressively evolved into more explicit quantitative performance and qualitative handling qualities standards now scattered throughout the Federal Aviation Administration (FAA) Title 14 Code of Federal Regulations (CFRs) Part 25 Subpart B Flight standards which are largely harmonized with other regulatory agencies. Recent rulemaking activity, including the potential branching of the regulatory structure to address modern fly-by-wire aircraft not envisioned at the inception of the original flight standards, have firmly engrained flight in icing certification as a major design consideration with potentially large economic disparities depending on the design approach. A discussion is then presented illustrating how the regulatory standards influence the design space; while some phases of flight can integrate icing considerations into the aircraft design such that there is no perceptible operational effect, other phases of flight may not be able to fully mitigate icing considerations through the basic aircraft design and performance and are therefore susceptible to appreciable operational and associated economic impacts borne by the operator. The focus of this paper is to provide awareness for how the philosophical approach to flight in icing certification has shaped the associated design landscape and highlight the importance of flight in icing certification in the design phase.