Redundant auxiliary power system for an aircraft, comprising: - an Auxiliary Power Unit "APU" for supplying power in an operative mode; - a normal and an emergency electric busbar networks; - a normal and an emergency starting means, both starting means (4, 5) being configured to independently start up the APU; - a normal and an emergency electric power generators, both electric power generators (6, 7) being configured to generate electric power when the APU is in the operative mode; the normal electric power generator being configured to supply electric power to the normal electric busbar network, and the emergency electric power generator being configured to supply electric power to the emergency electric busbar network, - an electrical power controller configured for controlling the electrical operational parameters of the normal and an emergency electric busbar networks; and - an APU controller connected to the electrical power controller and configured to control the operative mode of the APU based on data received from the electrical power controller, data related to the aircraft operational parameters, or a manually activated signal; wherein the normal and the emergency starting means are both configured to start up the APU for independently operating at least one of the normal and the emergency electric power generator; and wherein the redundant auxiliary power system is configured to operate according to: - an emergency mode wherein the APU controller is configured to activate: ∘ the emergency starting means to start up the APU, and ∘ the emergency electric power generator for supplying electric power to the emergency electric busbar network; or - a normal mode wherein the APU controller is configured to activate: ∘ one of the normal or emergency starting means to start up the APU, and ∘ one of the normal or emergency electric power generators for supplying electric power to the normal or emergency electric busbar network, respectively. - an Auxiliary Power Unit "APU" for supplying power in an operative mode; - a normal and an emergency electric busbar networks; - a normal and an emergency starting means, both starting means (4, 5) being configured to independently start up the APU; - a normal and an emergency electric power generators, both electric power generators (6, 7) being configured to generate electric power when the APU is in the operative mode; the normal electric power generator being configured to supply electric power to the normal electric busbar network, and the emergency electric power generator being configured to supply electric power to the emergency electric busbar network, - an electrical power controller configured for controlling the electrical operational parameters of the normal and an emergency electric busbar networks; and - an APU controller connected to the electrical power controller and configured to control the operative mode of the APU based on data received from the electrical power controller, data related to the aircraft operational parameters, or a manually activated signal; - an emergency mode wherein the APU controller is configured to activate: ∘ the emergency starting means to start up the APU, and ∘ the emergency electric power generator for supplying electric power to the emergency electric busbar network; or ∘ the emergency starting means to start up the APU, and ∘ the emergency electric power generator for supplying electric power to the emergency electric busbar network; or - a normal mode wherein the APU controller is configured to activate: ∘ one of the normal or emergency starting means to start up the APU, and ∘ one of the normal or emergency electric power generators for supplying electric power to the normal or emergency electric busbar network, respectively. ∘ one of the normal or emergency starting means to start up the APU, and ∘ one of the normal or emergency electric power generators for supplying electric power to the normal or emergency electric busbar network, respectively.