Carriers operating at Dublin have encountered a legal setback in their efforts to overturn a passenger cap at the Irish hub, after a high-level opinion advised that slot allocation can take into account passenger limits imposed by planning authorities.

The Irish Aviation Authority had warned in 2024 that it would impose a cap on passenger numbers at Dublin – restricting slot availability – because a planning condition for its terminal expansion restricted annual capacity to 32 million.

Airlines serving Dublin have argued that the planning condition is outdated and the cap, due to be implemented last year, was suspended pending a European Union legal ruling.

Court of Justice advocate general Manuel Campos Sanchez-Bordona has published a legal opinion that an annual passenger limit imposed by a planning authority can be taken into account during slot allocation.

Dublin airport has been slot co-ordinated since 2007, around the time when Irish planning authorities laid down the 32 million-passenger limit as a condition for terminal expansion.

Airlines have claimed that the limit is not a “technical, operational or environmental constraint” that must be taken into account, and also argue that the allocation of grandfathered slots is a right that cannot be compromised.

The Irish courts asked the Court of Justice to rule on these points, and to determine whether the airport’s operator is empowered to close the airport temporarily in order to comply with the restriction.

Sanchez-Bordona’s opinion, which is not binding, states that the technical, operational or environmental factors affecting airport capacity are “not only physical or material factors”, as the airlines suggest, but also the legal constraints which affect the airport’s use.

Compliance with the passenger limit can be classified as an operational constraint, he says, and the fact that it comes from a planning authority does not mean it stops being such.

Sanchez-Bordona also says the grandfathered slots are not property rights but authorisation to use airport infrastructure, and “cannot be granted in disregard of the airport’s capacity”.

He also believes that the question over the airport operator’s power to close the facility is “inadmissible”, submitting that such action to comply with a requirement known well in advance would be “excessively drastic”.