Ryanair should have compensated a passenger who saw their flight cancelled following the Icelandic volcanic ash cloud in 2010.
A ruling by the European Court of Justice found there is no limit in the duty of an airline to look after passengers during such an incident.
Denise McDonagh had a seven-day wait for a Faro-Dublin flight on Ryanair and claimed to have spent £968 on a hotel, food and transport.
Her compensation has not yet been paid.
Ryanair had argued the eruption of the Eyjafjallajokull volcano in Iceland was so unusual that is voided normal rules.
The court disagreed and said there was no limit on the time or money Ryanair was expected to invest in compensation.
The ruling stated “extraordinary circumstances” do no release air carriers from their obligation to provide care.
The ruling is now binding across the European Union.
The EU regulation on passenger rights “does not provide for any limitation, either temporal or monetary, of the obligation to provide care to passengers whose flight is cancelled due to extraordinary circumstances” the ECJ said.
“Thus, all the obligations to provide care to passengers are imposed on the air carrier for the whole period during which the passengers concerned must await their re-routing.”