Abstract: A spray cleaning device for cleaning an auxiliary power unit (APU) within an aircraft comprises one or more spray nozzles, a water tube for supplying water to the nozzles, and positioning means. A system for cleaning APUs comprises a spray cleaning device and a supply system for providing pressurized and temperature controlled washing fluid to the cleaning device. A method for cleaning APUs comprises providing a spray cleaning device, attaching the cleaning device to an air inlet structure of an aircraft, and supplying washing fluid to the cleaning device at a desired spray pressure, spray temperature, and spray droplet size.