The flight, arranged by travel agency Finnmatkat, had left Helsinki-Vantaa airport at 6:30 in the morning but turned back just 20 minutes after take-off.
Finnmatkat marketing director Tiina Sirén says that the smoke seems to have been caused by a piece of paper that ended up in the oven. Even though no smoke reached the passenger cabin, the crew decided to obey safety protocol and return to Helsinki.
The plane had its re-heating oven replaced, and left Helsinki again seven hours later, at around 13:30. Finnmatkat will not be paying passengers any compensation for the delay, as the law says no compensation needs to be paid for delays of less than eight hours.