Abstract: An auxiliary power unit (APU) for an aircraft utilizing solid oxide fuel cells for providing electrical power. The solid oxide electrolytes of the fuel cells allow for reformed fuel to provide a catalyst for oxygen migration. The auxiliary power unit, utilizing solid oxide fuel cells, can also power systems of the aircraft to produce water for use on the aircraft. Waste exhaust energy may be captured from the APU by a power recovery turbine which drives a compressor to provide aircraft cabin air under increased pressure to the fuel cell, thereby increasing system efficiency. The APU may provide all of the electricity to the aircraft allowing for more efficient aircraft engine design and a decrease in aircraft engine size. Furthermore, the fuel cell APU can reduce airport ramp noise and exhaust emissions.