The ECCOMAS 2026 STS session dedicated to the Project EFACA consists of 12 presentations related to a “Technological and Operational Roadmap for Greening of Aviation”, and the present paper 1 serves as an introduction. The EFACA Project involves 3 experimental demonstrations highlighted by: (Paper 2) The ground test bench of a hybrid turboelectric propulsion system consisting of a gas turbine and electric motor driving a 7-bladed propeller through a combiner gearbox; (Paper 3) A novel phase change cooling system for hydrogen fuel cells reducing heat losses and improving efficiency and suitability for operation at altitude; (Paper 4) As part of a complete laboratory liquid hydrogen fuel system, from tank to combustor, demonstration of an injector providing stable hydrogen combustion over a wide range of operating conditions. At level 2 greening technologies are considered for 4 classes of aircraft: (Paper 5) Battery power for small short-range aircraft like e-VTOLs; (Paper 6) Feedstocks, production paths, availability and cost of sustainable aviation fuels for large double aisle long-range airliners; (Papers 7/8) Design of a hybrid turboelectric propulsion system combining gas turbines and hydrogen fuel cells (Paper 7) and its application to a 80-seat 1000 km-range regional propeller aircraft (Paper 8); (Paper 9) Design of a 160-seat 2000 km-range jetliner with liquid-hydrogen fuel. At level 3 the environmental benefits of the level 1 technologies and level 2 aircraft designs are considered: (Paper 10) Reduction of the airport noise footprint, including flight and ground phases, for single aircraft and a whole fleet; (Paper 11) Likewise for carbon and other emissions affecting (a) local air quality near airports and (b) climate change on global scale; (Paper 12) A roadmap on the greening of aviation assessing the benefits of gradual replacement of current fleets by greener EFACA aircraft designs.