The Japan Transport Safety Board has determined that an engine fire on a Japan Airlines flight two years ago was caused by metal fatigue.
The fire was detected in the left engine of the Boeing 777 bound for New York shortly after it took off from Tokyo's Haneda Airport. The plane made an emergency landing at Haneda about an hour later.
The Transport Safety Board said in its report released on Thursday that the fire was caused by a broken fan blade.
The fan blade was found to be prone to fatigue because the engine's components were too close together and limited the blade's movement.
The US maker of the engine detected the same problem in an in-house test four years before the incident.
The firm redesigned its products, but did not ask airlines to urgently replace the engines.
Japan Airlines later found cracks in fan blades in two other engines.
The Transport Safety Board is calling for the replacement or repair of engine components and more frequent inspections.