Mainly owing to the dwindling fossil oil resources and the environmental concerns of discharging greenhouse gases into the atmosphere, it is essential to find an alternative to kerosene for civil aviation. This paper covers the main effects on aero engines when changing to hydrogen fuel. Particularly, emission and performance issues are discussed, but some design matters are also covered. By simply changing to hydrogen, small engine performance gains may be obtained. The results of the calculations suggest that there is the potential to design a combustion system using hydrogen that produces less emissions than any system using kerosene.