An inlet door system (109) including an aft inlet duct mounted door actuator providing RAM air to an auxiliary power unit (APU) (110) contained within an aircraft is provided. The inlet door system includes an inlet duct (120), the aft inlet duct mounted door actuator (134), and a door (130). The inlet duct (120) is configured to extend from the auxiliary power unit (110) to the aircraft housing and has a sidewall (126) that defines a flow passage. The door actuator (134) is mounted to an exterior surface of the aft portion of the inlet duct (120). The door (130) is coupled to the actuator (134). The actuator (134) is configured to selectively rotate the door (130) between at least a first position and a second position.