On Tuesday, a High Court judge indicated that resolving the challenges likely requires addressing questions of European law before the CJEU.

Mr. Justice Barry O’Donnell concurred with Aer Lingus and Ryanair that the most efficient approach would be to address the potential reference to the CJEU before a general hearing scheduled for next week.

The judge noted that EU law issues central to the airlines’ cases against the Irish Aviation Authority (IAA) have never been clarified by the CJEU. He described a reference to the European court as “almost an inevitability.”

National courts can seek guidance from the CJEU on unclear aspects of European law, and the court’s interpretation becomes binding across the EU.

Aer Lingus, Ryanair, and Airlines for America, which represents U.S. carriers, are challenging the IAA’s decision to impose passenger caps at Dublin Airport for both the winter and summer seasons. They argue the IAA improperly incorporated a 2007 planning condition—setting a separate annual passenger limit—in its capacity assessment.

Earlier this month, Mr. Justice O’Donnell granted the airlines’ urgent request to temporarily suspend the IAA’s decision to cap summer passenger numbers at 25.2 million. His order, which remains in effect until the cases are resolved, came shortly before the cap was to impact the allocation of summer take-off and landing slots at the airport.

On Tuesday, the judge reiterated that the cases involve unresolved EU law questions that are not “acte clair,” meaning they are not sufficiently clear to bypass a referral to the CJEU. He said clarity on these issues “can only be obtained by a reference.”

The High Court was scheduled to hear the substantive challenges to the summer and winter passenger caps over four days starting next Tuesday.

However, the judge agreed to delay the hearing until Wednesday, allowing time to address Aer Lingus and Ryanair’s request for a CJEU referral.

Suzanne Murray, senior counsel for Aer Lingus, argued that addressing the reference issue beforehand was the most time-efficient approach. Frank Crean, barrister for Ryanair, supported this, stating that a reference was “inevitable,” as the CJEU has never interpreted the EU’s slot regulation, which governs airlines’ take-off and landing rights.

The IAA and Dublin Airport operator DAA raised concerns that focusing on the reference could disrupt the substantive hearing. The IAA maintains it considered technical, operational, environmental, and local planning factors—such as An Bord Pleanála’s 2007 annual 32 million passenger cap for Terminal Two—when determining airport capacity.

Separately, the DAA has challenged the IAA’s cap of 14.4 million passengers for the winter period, arguing it is not stringent enough to prevent a breach of the 2007 planning condition. The DAA also contends that the EU slot regulation prevents it from “unilaterally” reducing passenger numbers to meet the condition.

Additionally, the DAA has applied to Fingal County Council to increase the 32 million annual passenger limit to 40 million.