More than 30 Ryanair passengers, some bleeding from their ears, were treated in hospital on Friday after their flight from Dublin to Croatia lost cabin pressure.
Ryanair has not yet given any reason for the incident on Flight FR7312, which had to make an emergency landing in Frankfurt.
The airline said oxygen masks were deployed and the crew carried out a ‘controlled descent’, after which a ‘small number of passengers received medical attention as a precaution’.
According to Flight Radar, the aircraft dropped 26,000ft.
Germany police said the plane was carrying 189 passengers, 33 of whom were hospitalised.
Passengers took to social media to complain they were not given enough food and drink and had been forced to sleep on a concrete basement floor or on camp beds.
Ryanair said it would pay for hotels for the passengers involved but said there was a ‘shortage of available accommodation’.
A spokesman added: "Customers boarded a replacement aircraft which departed to Zadar this morning and Ryanair sincerely apologised for any inconvenience."
The incident comes just days after an Air China flight from Hong Kong to Dalian suddenly lost pressure, causing oxygen masks to be deployed in the cabin for all passengers.
An initial investigation by China’s air regulator claims a co-pilot who was vaping in the cockpit was to blame.
Investigators say the co-pilot tried to hide the fact that he was smoking an e-cigarette but accidentally turned off the air-conditioning, instead of a fan, causing oxygen levels to fall.
