Aer Lingus, Ryanair, and a group of American airlines filed an urgent appeal against the Irish Aviation Authority’s (IAA) decision to cap passengers at 25.2 million between late March and October, arguing that the restriction would cause significant harm by reducing their access to “use them or lose them” slots.

The ruling comes just days before Airports Coordination Ltd (ACL) was due to allocate summer slots at Dublin Airport, a process that would have been constrained by the IAA’s cap.

Justice Barry O’Donnell stated that the airlines faced “immediate serious consequences” if he did not pause the IAA’s decision. He also noted that the potential risk of breaching planning conditions, as raised by the airport’s operator DAA, did not outweigh the “highly probable and very serious adverse consequences” for the airlines.

A full hearing to examine the airlines’ broader challenge to the IAA’s decision will take place at a later date.

In its decision on Dublin Airport’s capacity, the IAA considered technical, operational, environmental, and planning factors, including a separate annual limit of 32 million passengers imposed by An Bord Pleanála when approving Terminal Two in 2007.

Aer Lingus’ legal team argued that the 2007 limit should not have been a factor in the IAA’s recent capacity assessment, contending that its application for the winter 2024/25 season marked a departure from past practices.

Aer Lingus and Ryanair are also legally challenging a separate 14.4 million seat cap imposed for the winter season running from now until March 2025. The airport operator DAA is contesting this winter cap as well, arguing that it is too lenient and risks breaching the 2007 planning condition.

The High Court will hear those cases in December.

The IAA remained neutral on the airlines’ request for a stay but committed to defending its decision at the full hearing. The DAA opposed the request, asserting that suspending the cap would likely breach the 2007 condition, exposing the airport to enforcement actions and possible criminal penalties.

Meanwhile, DAA has applied to Fingal County Council to increase the 32 million cap to 40 million.

At the core of the airlines’ argument for suspending the summer 2025 cap is their right under EU law to retain “historic” slots. These slots operate on a “use them or lose them” basis, requiring 80% utilization in a season to secure them for the next year. The airlines argued that the IAA’s cap would cause them to lose some of these slots permanently.

Ryanair warned that losing historic slots at Dublin Airport would hinder its ability to retain equivalent slots at 67 other European airports.

Airlines for America, representing U.S. carriers, claimed the cap would lead to “very significant financial losses,” undermining an airline’s core business.

In opposition, DAA’s senior counsel argued that the passenger cap for 2007 would be breached this year and again next year if the IAA’s summer cap was lifted. Counsel for DAA, Fintan Valentine, explained that as the airport operates in a “heavily regulated environment,” EU regulations prevent it from unilaterally reducing passenger numbers to comply with the 2007 limit. He stated that the DAA had asked airlines to voluntarily lower passenger numbers, but they refused, putting DAA at risk of violating planning permissions.