European carriers must pay the hotel and meal costs for passengers if they are stranded overseas, even if the delays are caused by natural disasters.
The new ruling comes after Dubliner Denise McDonagh took a long shot case against low cost carrier Ryanair because it has refused to pay her claim of $1,498.00 after she was stranded for a week in Portugal during the Icelandic ash crisis of 2010.
Ryanair had argued that the closure of all airspace following the eruption was completely extraordinary, so much so that EU 261 - the rule that obliges airlines to look after customers - should not apply.
However, the Advocate General of the European Court found that the ash cloud crisis was covered by the 'extraordinary circumstances' provision of EU 261, leaving the airline liable to pay McDonagh's costs.
According to a report in the Irish Independent, the ruling is provisional and the opinion is not binding on the Luxembourg court, but it is upheld in 80 percent of cases.
McDonagh was scheduled to fly home from Faro in Portugal on April 17, 2010, but because of the ash cloud she was unable to until April 24, resulting in her claim for $1,498.00 in damages from Ryanair to cover the cost of her meals, accommodation and transport.
Ryanair told the Irish Independent that it had taken a stance against McDonagh's claim as a test case to address the EU261 rules, which it considers hugely unfair.
However, Yves Bot, the Advocate General, found that the term "extraordinary circumstances" covered all circumstances over which the air carrier has no control.
Bot also found it was not disproportionate to impose this long established rule on the airline, as they were free to pass on the costs on to passengers though ticket prices, as Ryanair had already imposed on every ticket sold.
However, Ryanair are reluctant to concede the ruling yet, spokesman Stephen McNamara told the Independent that this weeks opinion was not binding.
"We hope the final court decision will find in favour of Ryanair's appeal," he said.