Smoke appeared in the cockpit of an EasyJet flight due to an electrical fault known to the manufacturer, an investigation has found.
EasyJet was unaware 10 similar failures had been reported previously, according to the Air Accidents Investigation Branch (AAIB).
The captain and first officer became aware of smoke and fumes 11 minutes after taking off from Edinburgh.
There were 172 passengers on board the flight on 28 November 2016.
The pilots were forced to wear their oxygen masks, issue a mayday alert and divert the Airbus A320 to Newcastle.
The source of the smoke was traced to an overheated device which converts voltage in the cockpit, the AAIB found.
Aircraft manufacturer Airbus did transmit warnings about the problem but they were in a format used for "information" rather than "instructions" and were not routinely reviewed by EasyJet.
Another "large UK operator" also did not regularly study these messages, the inquiry revealed.
EasyJet believes the defect should have been "classified as a safety issue" and communicated to carriers in higher-profile alerts.
Both the aircraft manufacturer and the airline "intend further safety action", the AAIB stated.
There was also a three-minute delay in the co-pilot being able to speak to cabin crew due to difficulties using the aircraft's phone system.
The incident occurred on flight EZY6931 from Edinburgh to Hamburg in Germany.
The aircraft landed safely in Newcastle and the passengers were able to disembark normally.