Passengers suffered eye and throat irritation when fumes and smoke got into the cockpit and cabin of their aircraft, an accident report said.
It happened on an easyJet flight from Newcastle to Budapest last December, carrying 128 passengers and five crew.
An Air Accident Investigation Branch (AAIB) report said the fumes were from de-icing fluid entering an air inlet.
The report added that easyJet had agreed to remind those who de-ice aircraft to take more care.
At one point thick black smoke was seen in the cockpit of the Boeing 737 and pilots donned oxygen masks and the plane returned to Newcastle where some passengers were offered medical help.
The incident happened about six miles out from Newcastle on the evening of 28 December 2005.