A propulsion system (20, 120, 220) for an aircraft, the propulsion system (20, 120, 220) comprising a propeller assembly (22, 122, 222) that includes a propeller (23, 123, 223) configured to rotate around a central axis and a power system (26, 126, 226), the power system (26, 126, 226) including an electric motor mechanically coupled to the propeller (23, 123, 223) and configured to drive the propeller (23, 123, 223), and a motor converter (30, 130, 230) electrically connected to the electric motor and configured to deliver electric power to the electric motor, a controller (42, 142, 242) connected to the power system (26, 126, 226) and configured to switch the power system (26, 126, 226) into a power-off arrangement in which the motor converter (30, 130, 230) is powered off and blocked from delivering the electric power to the electric motor in response to a temperature of the motor converter (30, 130, 230) being greater than a predetermined threshold temperature, and a pump system (34, 134, 234) including a pump (36, 136, 236) and a coolant circuit (38, 138, 238), the pump (36, 136, 236) configured to pump coolant through the motor converter (30, 130, 230) via the coolant circuit (38, 138, 238) so as to cool the motor converter (30, 130, 230), characterised in that the pump (36, 136, 236) is mechanically coupled to the propeller (23, 123, 223) and to the electric motor such that rotation of any one of the propeller (23, 123, 223) and the electric motor drives the pump (36, 136, 236) such that rotation of the propeller (23, 123, 223) drives the pump (36, 136, 236) to move the coolant through the coolant circuit (38, 138, 238) and lower the temperature of the motor converter (30, 130, 230) to less than the predetermined threshold temperature in response to the motor converter (30, 130, 230) being in the power-off arrangement during operation of the propulsion system (20, 120, 220). a propeller assembly (22, 122, 222) that includes a propeller (23, 123, 223) configured to rotate around a central axis and a power system (26, 126, 226), the power system (26, 126, 226) including an electric motor mechanically coupled to the propeller (23, 123, 223) and configured to drive the propeller (23, 123, 223), and a motor converter (30, 130, 230) electrically connected to the electric motor and configured to deliver electric power to the electric motor, a controller (42, 142, 242) connected to the power system (26, 126, 226) and configured to switch the power system (26, 126, 226) into a power-off arrangement in which the motor converter (30, 130, 230) is powered off and blocked from delivering the electric power to the electric motor in response to a temperature of the motor converter (30, 130, 230) being greater than a predetermined threshold temperature, and a pump system (34, 134, 234) including a pump (36, 136, 236) and a coolant circuit (38, 138, 238), the pump (36, 136, 236) configured to pump coolant through the motor converter (30, 130, 230) via the coolant circuit (38, 138, 238) so as to cool the motor converter (30, 130, 230), characterised in that the pump (36, 136, 236) is mechanically coupled to the propeller (23, 123, 223) and to the electric motor such that rotation of any one of the propeller (23, 123, 223) and the electric motor drives the pump (36, 136, 236) such that rotation of the propeller (23, 123, 223) drives the pump (36, 136, 236) to move the coolant through the coolant circuit (38, 138, 238) and lower the temperature of the motor converter (30, 130, 230) to less than the predetermined threshold temperature in response to the motor converter (30, 130, 230) being in the power-off arrangement during operation of the propulsion system (20, 120, 220).