Smoke appeared in the cockpit of an easyJet flight due to an electrical fault which was known to the aircraft manufacturer, an investigation has found.
EasyJet was unaware that 10 similar failures had been reported previously, according to the Air Accidents Investigation Branch (AAIB).
The captain and co-pilot became aware of smoke and fumes just 11 minutes after taking off from Edinburgh with 172 passengers on board.
They were forced to don 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.
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, Germany, on November 28 last year.
The aircraft landed safely in Newcastle and the passengers were able to disembark normally.
An easyJet spokeswoman said: "Safety critical instructions communicated to easyJet via Airbus are always reviewed and acted upon at the time of publication.
"We raised this as a concern with Airbus following the diversion.
"The safety of its passengers and crew is easyJet's highest priority and easyJet operates its fleet of aircraft in compliance with all manufacturers' guidelines."