Civil aviation is an attractive target for criminals and terrorists in part because great harm can be done with relatively few resources. Why is it that some attacks against civil aviation prompt great change in government public policy towards aviation security, and others cause relatively little? Four independent variables were identified that cause the greatest variation in public risk perception in response to an attack: its size, target, nature of the perpetrators of the event, and ingenuity. The size and scope of policy change was categorized utilizing Hall's Order of Change model. It was found that events of large size, targeted against the state, by a credible and known perpetrators capable of repeating an ingenious attack causes the greatest shift in public risk perception, which results in the largest policy changes. The size and scope of policy change is proportional to changes in public risk perception.