A crash attenuation system for an aircraft includes an airbag carried by the aircraft that is inflatable generally adjacent an exterior of the aircraft. The airbag is in fluid communication with at least one vent passage for channeling gas from within the interior of the airbag to a region external to the airbag that allows the gas to escape without being obstructed by the airbag. A gas source is in fluid communication with the interior of the airbag for inflating the airbag. A vent valve is provided within the vent passage for controlling a flow of gas through the vent passage, thereby controlling deflation of the airbag. The vent valve is continuously adjustable to and between an open state, a closed state, and any number of partially open states.