## 1 Introduction  
The aviation sector is highly dependent on finite fossil fuel reserves. This dependency creates energy insecurity for many nations because of unpredictable pricing and reliance on a limited number of foreign suppliers for fossil fuels [1]. Hence, hydrogen has emerged as an increasingly attractive alternative to address these vulnerabilities by offering nations a pathway toward greater energy independence. Unlike conventional jet fuel, nations can produce hydrogen from diverse resources [2]. Furthermore, analysts expect that future technological advancements will significantly enhance the economic viability of hydrogen as an alternative source of energy [3]. However, significant technical and operational barriers remain, particularly in fuel storage, delivery, thermal management, and integration with the existing airframe and propulsion systems [4]. For instance, storing and transporting hydrogen efficiently requires compression or liquification processes that require cryogenic conditions at extremely low temperatures [5]. Even so, liquid hydrogen requires four times the storage volume compared with conventional jet fuel [6]. This difference in volumetric energy density presents major challenges in aircraft design and operational feasibility. Likewise, the development of efficient hydrogen combustion and hybrid electric propulsion systems is still in the early stages. Weight constraints, power density limitations, and safety concerns limit progress in hydrogen-powered aircraft development [1]. While research hasproposed various technologies to address these issues, it remains unclear which innovation pathways are most promising and actively pursued toward commercial realization. The current research on hydrogen-powered aviation focuses on experimental designs, demonstrator aircraft, and feasibility studies [7]. While these efforts provide valuable theoretical insights, they often overlook practical innovation trajectories reflected in industrial patent filings [8]. Patents serve as early indicators of technological direction, revealing practical advancements, commercialization trends, and innovation bottlenecks. Furthermore, unlike conventional literature reviews that focus more on academic developments, patent analysis can provide organizations with market intelligence; support strategic planning; assess the commercial value of their intellectual property portfolio; identify collaborators, business partners, and competitors; and adapt to evolving regulations and standards [9]. Currently, the scholarly literature lacks a comprehensive patent-based analysis that systematically categorizes emerging hydrogen aviation technologies. This research gap makes it difficult to assess innovation trends, competitive landscapes, and research priorities. The goal of this paper is to analyze patents in hydrogen-powered aircraft to classify key innovation areas and uncover trends influencing adoption. The unique methodology employed is a systematic analysis of the claims section of patent filings to uncover the dominant innovation trends in hydrogen-powered aircraft. The existing patent research analyzed mostly the titles and abstracts of patents rather than their claims [10]. In so doing, they could misrepresent the actual protected innovation and miss the scope of protection. Hence, this research uniquely focuses on the claims sections of the patents analyzed. In particular, the key contributions of this study are as follows:  
1. Patent-based categorization of hydrogen as an aviation fuel, providing a structured classification of innovations across critical areas. 2. Identification of emerging innovation trends, highlighting active research and development directions in hydrogen-powered aircraft. 3. Industry and policy insights, informing aerospace companies, researchers, and policymers on key innovation pathways and technology gaps to accelerate sustainable aviation.