AIRCRAFT PROPULSION SYSTEM

An aircraft propulsion system (100) comprises a gas turbine engine (140) arranged to provide propulsive thrust and a fuel cell system (152) having an air input port (155), the aircraft propulsion system being configured such that air from a compressor (112) of the gas turbine engine is provided to the air input port during operation of the aircraft propulsion system. The fuel cell system is able to provide appreciable electrical power at altitude without the need for a dedicated compressor.