There are three main theoretical difficulties involved in relating sustainability to aviation, and which a research agenda for sustainable aviation needs to address. The first is uncertainty regarding the critical thresholds of global environmental systems. The second is a lack of protocols for allocating permissible environmental consumption shares to, and hence targets for, individual enterprises or sectors. The third is differing value judgements of what natural features should be sustained. For the time being, these difficulties preclude determination of the degree of sustainability or unsustainability of any individual airport with respect to global environmental systems. Nevertheless, at this stage it can at least be said that since most economic activity has an adverse environmental impact, airports with higher throughputs of material and people will tend to be less sustainable than smaller-scale airports given similar technologies and regulatory compliance. This is theoretically supported and illustrated with waste arising as an indicator at reviewed airports. Despite governmental policies of sustainable mobility, there is a disjunction between EU and UK policy on airports and individual airport practice, and environmental sustainability theory. In the UK and EU, airport practice and governmental policy is to mitigate the impacts of aviation, but not at the expense of its aviation growth. This mitigation practice is summarised for the reviewed airports and presented in a framework that accounts for the suggested, interim approach to sustainability assessment.