The categorization of traditional commercial airplanes can be delineated into three primary classifications: single-aisle (narrow-body), twin-aisle (wide-body), and regional aircraft, the latter being the smallest variant. This categorization serves as a foundational framework for comprehending the dimensions and passenger capacities of these aircraft. It is equally applicable when considering the integration of groundbreaking hybrid technologies and fuel cells in the aviation sector. Aircraft employing all-electric and hybrid propulsion systems, characterized by propeller-driven flight, demonstrate performance characteristics akin to turboprop aircraft. Consequently, there is an anticipation that hybrid aircraft are the future of the regional market, they may supplant turboprop models but might not necessarily replace conventional jet aircraft. Before the advent of the COVID-19 pandemic, the realm of regional aviation witnessed substantial growth, contributing to more than 12% of global available seat kilometers (ASK). However, the aftermath of the pandemic significantly impacted both worldwide economic progress and air travel, initiating a gradual recovery process. Projections indicate that global passenger traffic, quantified in revenue passenger kilometers (RPK), is poised to reach pre-pandemic 2019 levels by 2024. This recovery is driven by factors such as pandemic recuperation efforts, geopolitical considerations, and shifts within the aviation industry. Forecasts suggest that global RPKs will experience a consistent annual growth rate of 3.2% until 2042. The translation of this overall growth into the regional aviation market and the evolving dynamics that steer the regional market will profoundly influence the adoption and success of innovative hybrid aviation technologies. Within this context, the EFACA Project (Environmentally Friendly Aviation for All Classes of Aircraft), funded by the European Union between 2023 and 2026, is actively engaged in developing a hybrid turbine-electric propeller (HTEP) aircraft system incorporating fuel cells. This system is designed for regional aircraft with a seating capacity of up to 80 and a range extending to 1000 km. The EFACA project adopts a systematic approach to define the HTEP design, commencing with the establishment of top-level requirements for both the HTEP system and the aircraft. The subsequent stages involve assessing conceptual frameworks for the HTEP power supply, preliminary formulation of HTE