May 6 (Reuters) - Delta Air Lines ( DAL ) must face a

proposed class action by passengers who said it refused to offer

full refunds after delaying or canceling their flights following

a massive computer outage last July, a federal judge ruled on

Tuesday.

U.S. District Judge Mark Cohen in Atlanta said five of the

nine plaintiffs may pursue breach of contract claims based on

Delta's failure to refund.

The judge allowed a different group of five plaintiffs to

pursue claims related to delayed and canceled flights under the

Montreal Convention, a multilateral treaty.

Cohen dismissed the remaining claims, including those he

said were preempted by federal law.

The July 19, 2024 outage stemmed from a flawed software

update from cybersecurity company CrowdStrike ( CRWD ) that

crashed more than 8 million computers and affected many

Microsoft ( MSFT ) customers.

Disruptions eased the next day for many U.S. airlines but

lasted longer at Delta, which canceled about 7,000 flights.

"This ruling is a major step forward for Delta passengers

seeking accountability," Joseph Sauder, a lawyer for some of the

plaintiffs, said in an email.

Neither Delta nor its lawyers immediately responded to

requests for comment.

The Atlanta-based carrier had sought the dismissal of all

claims, aside from one refund claim and international travelers'

claims under the Montreal Convention.

Passengers accused Delta of failing to provide automatic

refunds following the outage, and providing partial refunds only

if they waived further legal claims.

One plaintiff, John Brennan of Florida, said he and his wife

missed a $10,000 anniversary cruise after Delta stranded them in

an Atlanta layover, yet the carrier offered just $219.45 in

compensation.

Another plaintiff, Vittorio Muzzi of the Netherlands, said

he spent 5,000 euros ($5,685) and his luggage was delayed 15

days after Delta scrapped his flight to Florida from Amsterdam,

yet the carrier offered just 588 euros ($669) in compensation.

Delta has estimated that the outage cost $550 million in

lost revenue and added costs, while saving $50 million of fuel.

The case is Bajra et al v Delta Air Lines ( DAL ), U.S. District

Court, Northern District of Georgia, No. 24-03477.

(1 euro = $1.137)