The aviation industry has grown at a steady rate of 5% per year over the past decades and is projected to continue this growth over the coming years. In sharp contrast stands the increasing concern with the reduction of the environmental impact of flying in the short term. To this end, a fuselage boundary layer ingesting propulsor powered using hydrogen combustion is proposed to replace the conventional APU on the next-generation version of the Airbus A321neo. This study concludes that up to 10% of the required shaft power can be provided by the third engine, resulting in a 1% reduction in mission energy consumption and an 11% reduction in CO2-emissions. The concept aircraft's mass is similar to the baseline aircraft. Water vapour emissions are expected to rise by 14%.