A power generation system includes a ram air turbine that is connected to a generator. The power generation system may be located in a pod, for example a pod for mounting on an aircraft. The ram air turbine receives air that passes through an air path through the pod, going in through an air inlet, through the turbine to turn the turbine, and out through an air outlet. The system includes a deployable flow obstruction, such as one or more airbags, that are deployable to suddenly obstruct the flow through the air path. The obstruction may be used to cut off flow (or greatly reduce flow), when overspeed of the ram air turbine is detected. The obstruction deploys (for example, airbags deploy in an air inlet of the system) to prevent continuation of the overspeed operation of the turbine, which may damage parts of the system.