A couple onboard a Ryanair flight described the terrifying moment they heard a "bang" followed by a rush of cold air before oxygen masks dropped and the plane started to descend.
Melvin Frater and his wife Jacqueline, from Nottingham, were flying back from Milan to East Midlands Airport on a Ryanair Boeing 737-800 on Wednesday when depressurisation incident occurred.
Three people were taken to hospital for precautionary examination following the incident, Ryanair confirmed.
The captain was calling out "Mayday" over the speaker system as they made an emergency descent due to loss of cabin pressure.
He said he could see snow-covered mountains "approaching fast" out of the windows of flight FR 1703, which was carrying 134 passengers from Milan Bergamo airport.
"We were approximately 20 minutes into the flight when we felt and heard a bang, followed by a rush of very cold air, rushing by our feet, from the front to the back of the plane, Mr Frater said.
"This was immediately followed by the deployment of the oxygen masks and the plane began to make a rapid descent."
Mr Frater said children and babies started to cry but passengers remained calm and followed the safety procedures.
He said: "It was quite strange that, unlike the scenes of panic and screaming which accompany cinema portrayals of such situations, there was initially a real sense of calm and quiet - we just followed safety procedures.
"The captain could then be heard over the speaker system - whether this was supposed to be heard by the passengers I do not know - but it was very unnerving to hear him say something like '...we are making an emergency descent due to loss of cabin pressure. Mayday!'."
He said once the plane had levelled out, the air crew told them the oxygen masks were no longer needed.
The captain apologised and explained to passengers over the speaker system that the crews had followed the correct procedures to cope with sudden loss of pressure and they had reduced altitude to just 9,000 feet, Mr Frater said.
The plane was diverted to Frankfurt Hahn airport, where they were later transferred to a different plane and flown back to East Midlands Airport.
In a statement, Ryanair apologised to passengers for the incident.
It said three people were taken to hospital for precautionary checks with ear pain concerns but were released shortly afterwards.
No passengers were injured during the depressurisation incident, the airline said.
In a statement, Ryanair said: "Flight FR1703 (Milan to East Midlands) diverted to Frankfurt Hahn after the captain identified a pressurisation warning, deployed the oxygen masks, and descended to 10,000ft as recommended.
"The aircraft landed at midday (local time) and passengers disembarked normally, to be provided with refreshments.
"A replacement aircraft took them onwards to East Midlands Airport with an estimated delay of four hours.
"Ryanair apologises sincerely to all passengers affected by this diversion and delay."