Recognizing the attention currently devoted to the environmental impact of aviation, this three-part publication series introduces two new aircraft propulsion concepts for the timeframe beyond 2030. This first part focuses on the steam injecting and recovering aero engine (SIRA) concept. Exhaust heat generated steam is injected into the combustion chamber. By use of a condenser, installed behind the steam generator, the water is recovered from the exhaust gas–steam mixture. Both lead to a noticeable increase in specific power compared to a conventional gas turbine and, foremost, to a significant increase in thermodynamic efficiency. The proposed concept is expected to reduce fuel burn and carbon dioxide (CO2) emissions by about 15% and nitrogen oxides (NOx) formation can be almost completely avoided compared to state-of-the-art engines of the same technology level. Moreover, the described concept has the potential to drastically reduce or even avoid the formation of condensation trails. Thus, the SIRA concept operated with sustainable aviation fuels offers the potential for climate-neutral aviation. Based on consistent thermodynamic descriptions, preliminary designs and initial performance studies, the potentials of the concepts are analyzed. Complementarily, a detailed discussion on concrete engineering solutions considers the implementation into aircraft. Finally, the impact on emissions is outlined.