By Simon Hradecky, created Monday, Feb 22nd 2021 13:54Z, last updated Tuesday, Mar 9th 2021 14:19Z

A JAL Japan Airlines Boeing 787-9, registration JA867J performing flight JL-48 from Helsinki (Finland) to Tokyo Haneda (Japan), was enroute at FL370 about 600nm eastnortheast of Helsinki in Russian Airspace when the crew decided to turn around and return to Helsinki due to right hand engine (GEnx) vibrations. The aircraft initially descended to FL360 for the return and later drifted down to FL280. The aircraft landed safely on Helsinki's runway 04L about 2:40 hours after leaving FL370 with both engines operating normally.

Finland's On­net­to­muus­tut­kin­ta­kes­kus (Accident Investigation Board AIBF) reported they have been looking into the occurrence of engine vibration, however, found no grounds to open an investigation. However, a report is to be expected in a couple of days. The crew decided to not continue the flight in case the engine's condition worsened over the Tundra ahead.

On Mar 8th 2021 the On­net­to­muus­tut­kin­ta­kes­kus released their report in Finnish concluding the probable causes of the incident were:

- The aircraft turned back for technical reasons, although according to FCOM the crew could have continued the flight despite the engine vibrations. The change in the flight path demonstrated proactive safety thinking and consideration of economic impacts.

- A piece of a fan blade coating separated causing an imbalance in the engine, which the vibration sensor detected. The aircraft systems detected a deviation the performance for which the engine manufacturer had not specified any limit. Acceptable vibration limits had only be set for takeoff.

The AIBF reported, that the Japan Airlines flight (JL48) had departed from Helsinki-Vantaa Airport on February 21, 2021 at 6:21 p.m. towards Tokyo Haneda Airport. Due to the vibration of the right engine during the flight, the pilot made the decision to return to Helsinki because of the long flight ahead in Russian airspace and because of difficulties to obtain technical assistance in the alternate aerodromes along the route ahead. The aircraft turned around about 80 minutes after departure to return to Helsinki. The engine that gave the vibration indification was not shut down, however, in accordance with standard procedures the pilots significantly reduced their altitude and airspeed. During the approach to Helsinki all indications of both engines were normal. The flight landed on runway 04L at 10:02 p.m. The aircraft was examined by Japan Airlines' line maintenance organisation and remained to be repaired.

The detached piece of coating was found in the bypass duct bent around and stuck at a first stage stator blade of the fan. The assessment of engine airworthiness, incident report, determination of cause of the separation of the coating as well as corrective actions were performed in accordance with methods and standards approved by the maintenance origanisation contracted by JAL.