The STS is based on the project EFACA (Environmentally Friendly Aviation for All Classes of Aircraft) that is supported by the European union in the period 2023-2026. It is intended to give a global overview of the challenges associated with the greening of aviation, taking as example an 80-seat 1000-km regional airliner with hybrid turboelectric propulsion, and including (i) overall design, (ii) critical technologies, (iii) economic and market prospects and (iv) environmental benefits. The STS consists of presentations addressing the following topics: • Overview of all aspects of the project EFACA, with focus on those aspects that have been selected for the following seven presentations in this STS. • Preliminary design of an 80-seat 1000 km range regional airliner with hybrid turboelectric propulsion (HTEP) consisting of gas turbine and hydrogen fuel cell. • The most innovative element of the electrified regional airliner, namely the HTEP system as concerns components and integration. • One of the critical technologies for HTEP, concerning cryogenic fuel tanks for liquid hydrogen bearing in mind their larger volume compared with traditional fossil fuels for the same range. • Another of the critical technologies for HTEP, namely hydrogen fuel cells with particular challenges of cooling and efficiency at altitude for aeronautical applications. • Market prospects of the regional aircraft using HTEP as a replacement for existing fossil fuelled airliners, bearing in mind the additional complexity (preceding presentations) and environmental benefits (following presentations) and their impact on economics and operations. • Benefits of a regional airliner using HTEP as concerns reductions of environmental impact in terms of emissions and noise at airport and global level. • Sustainable Aviation Fuels (SAFs) focusing on alternative technologies for the production of alternatives to current fossil fuels.