Delta Air Lines must face a proposed class action lawsuit by passengers who claim the carrier refused to provide full refunds after a massive computer outage disrupted flights last July, a federal judge has ruled.

US District Judge Mark Cohen in Atlanta determined on Tuesday that five of the nine plaintiffs may pursue breach of contract claims based on Delta's alleged failure to offer refunds.

The judge also permitted a different group of five plaintiffs to pursue claims related to delayed and cancelled flights under the Montreal Convention, a multilateral treaty governing international air travel.

Judge Cohen dismissed the remaining claims, including those he deemed were preempted by federal law.

The computer outage on 19 July 2024 originated from a flawed software update from cybersecurity company CrowdStrike that crashed more than 8 million computers and affected numerous Microsoft customers.

While disruptions eased the following day for many U.S. airlines, they persisted longer at Delta, which ultimately cancelled approximately 7,000 flights.

"This ruling is a major step forward for Delta passengers seeking accountability," said Joseph Sauder, a lawyer representing some of the plaintiffs.

Passengers have accused Delta of failing to provide automatic refunds following the outage and offering only partial refunds contingent upon passengers waiving further legal claims.

One plaintiff, John Brennan of Florida, claimed he and his wife missed a $10,000 anniversary cruise after Delta stranded them during an Atlanta layover, yet the carrier offered just $219.45 in compensation.

Another plaintiff, Vittorio Muzzi from the Netherlands, reported spending 5,000 euros and experiencing a 15-day luggage delay after Delta cancelled his flight from Amsterdam to Florida. The carrier allegedly offered him only 588 euros in compensation.

Delta has estimated that the outage cost $550 million in lost revenue and additional expenses, while saving $50 million in fuel costs.

Neither Delta nor its legal representatives immediately responded to requests for comment on the ruling.

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