The plane was diverted to Cologne Bonn Airport about 30 minutes after it departed London Gatwick Airport for Paphos, Cyprus.
Flight EZY5455, carrying 169 passengers and six crew, was near the Belgium-Luxembourg border when the emergency was declared and it changed course towards the airport between the German cities of Cologne and Bonn.
The passenger said emergency procedures were employed thereafter and the Airbus A320 made a rapid descent from 33,000ft in about 15 minutes.