EU Court of Justice Rules Legal Airport Caps Must Be Considered in Slot Allocation, Citing Dublin's 32 Million Passenger Limit

The Court of Justice of the European Union (CJEU) ruled on October 15, 2026 that legal airport caps must be taken into consideration when determining annual traffic capacity under the EU Slot Regulation. The Court confirmed that airport slots can be reduced under the Regulation if constraints are in place, such as an annual passenger limit.

The ruling answered three questions referred by the Irish High Court. Dublin Airport has a limit of 32 million passengers per year, which was exceeded in 2023, 2024 and 2025. In 2024, the Irish Aviation Authority (IAA), the independent state regulator, drew up coordination parameters under the Slot Regulation for winter 2024 and summer 2025, including measures to keep passenger numbers within the cap. The Dublin Airport Authority (daa), which runs Dublin and Cork airports, and several airlines appealed to the High Court. In November 2024 the High Court provisionally suspended implementation of the parameters.

The CJEU held that 'all relevant' technical, operational or environmental factors affecting airport capacity include not only physical factors but also legal constraints to the extent they affect use of the airport. It described the term as broad enough to cover constraints 'whatever they may be', whether political, legal or physical, and whether long-standing or subsequently evolved. It found that compliance with the 32 million passenger limit at Dublin Airport can be classified as an operational constraint to be considered by the IAA when designating coordination parameters.

Opportunity Green welcomed the ruling and said it aligns with the legal opinion it commissioned in October 2025 from Tiffany Tang of Fountain Court Chambers. That opinion found that climate laws legally requiring reduced airport capacity qualify as environmental constraints, that broader measures such as national carbon budgets may also count if they affect airport infrastructure, and that carriers hold no proprietary right to historic slots.

Denise Auclair, head of T&E's Travel Smart Campaign, said the decision has implications for other countries where industry is challenging the relevance of airport capacity limits.

The Dublin Airport (Passenger Capacity) Bill 2026, enacted in February 2026, gives Ireland's Minister for Transport authority to amend or remove the passenger limit. The daa has formally asked the Minister to invoke the Bill to raise the cap, a decision that must be informed by an environmental impact assessment of the additional aircraft emissions.

Sorcha Tunney of Opportunity Green said the ruling does not itself prevent the Irish government from pursuing removal of the cap but clarifies the legal significance of capacity constraints.

Under Article 6(1) of the Slot Regulation (Regulation (EEC) 95/93), slots at coordinated EU airports are allocated twice yearly while taking account of all relevant technical, operational and environmental constraints. The CJEU's reading means a legally imposed cap, such as Dublin's passenger limit, sits inside that exercise rather than outside it, and slot reductions can follow from it. For airlines, historic slot positions at capped airports are therefore exposed to legal limits on total traffic.

The 'use it or lose it' rule in Article 8(2), under which an airline may be entitled to the same series of slots if it has operated them for at least 80% of the allocated time, protects continuity of use but does not override a capacity ceiling set by law. The practical question for any capped airport is how coordination parameters are set against that ceiling each season.

The next concrete decision is the Irish Minister for Transport's response to the daa's formal request to raise the cap under the 2026 Bill, which must be informed by an environmental impact assessment of the additional aircraft emissions. The High Court proceedings that prompted the referral also remain the setting in which the IAA's parameters are tested.