This article analyses the expansion of European Union cooperation on aviation security using the framework of collective securitisation. It establishes how 9/11 was a precipitating event which put terrorism and aviation security in the spotlight. 9/11 changed the collectively held understanding of the security threat posed by terrorism sufficiently to establish aviation security as a common policy framework rather than a national issue, as it was previously considered to be. 9/11 was therefore used by EU actors to convince the EU member states that they all faced one collective terrorist threat, rather than each of them facing a distinctive threat. The subsequent institutionalisation of this cooperation contributed to a routinisation of aviation practices in the EU. As a result of the association between terrorism and aviation, 9/11 pushed EU member states into taking action on aviation security. This caused the member states to acknowledge the need for both the highest possible standards of aviation security but also the harmonised enforcement of these standards.