Every military aircraft that a European state keeps available depends on maintenance that someone is legally entitled to perform and certify, and as European states rebuild their military capacity, the question of who may perform that work across national borders becomes a question of usable capacity. Europe’s military airworthiness authorities have worked for more than a decade on a common European model of maintenance requirements. It would be natural to assume that this alignment has produced a single maintenance market in which an approved supplier in one country can work on another country’s military aircraft. It has not, and the reason is structural rather than bureaucratic: military airworthiness remains a national responsibility, and each state decides whose regulatory work it is prepared to rely on. The practical question for ministries, procurement agencies, prime contractors, maintenance suppliers and the investors who finance them is therefore narrower and more consequential than whether European rules have been harmonised. It is when, and under what conditions, an approval that a supplier already holds from its own authority can be used for another European state’s aircraft, and what else must be in place before that approval turns into work that can lawfully be contracted, performed and released.