Large investments have already been made in Europe and the US through R&T programmes and collaborations to reduce the negative environmental effects of aircraft use. Research is therefore providing the technologies to improve the performance of existing engine components. The main objective of the paper is to evaluate the potential of reducing the environmental impact of civil subsonic aviation by using hydrogen fuel. Looking at the prospect of alternative fuels, synthetic kerosene produced from biomass turns out to be feasible and offers environmental benefits in the short run, whereas hydrogen seems to be the more attractive alternative in the long run. Powering aero engines and aircraft with hydrogen has been done successfully on a number of occasions in the past.