Incident Overview
On February 21, 2021, Japan Airlines flight JL48, a Boeing 787-9 Dreamliner, departed Helsinki-Vantaa Airport at 18:21 local time bound for Tokyo Haneda Airport. After 1 hour and 20 minutes of flight, the captain decided to return to Helsinki due to vibration in the right engine. The aircraft landed on runway 04L at 22:02 without further incident.
Technical Details
The aircraft is a twin-engine widebody airliner powered by General Electric GEnx-1B turbofan engines. The fan blades and fan case are made of carbon-fiber composite to reduce weight and fuel consumption. The flight crew did not shut down the affected engine and reduced altitude and speed in accordance with standard procedures. During the approach to Helsinki, all engine indications were normal.
Weather Conditions
At departure, the weather was cloudy with freezing drizzle, temperature –3°C, wind from 120° at 6 m/s, ceiling 180 m, visibility 5000 m. At arrival, conditions were similar with temperature –6°C, wind from 100° at 5 m/s, visibility 7000 m.
Emergency Response
The rescue department of Central Uusimaa was alerted by air traffic control at 21:15. First rescue units arrived at 21:26, and the alert was terminated at 22:05.
Post-Flight Inspection
After landing, a technical inspection found that a piece of coating had detached from a fan blade of the right engine, measuring approximately 5 x 20 cm. The detached piece was found bent and entangled in the first-stage stator vane in the bypass duct. The engine's airworthiness assessment, defect reports, and repair procedures were handled by Japan Airlines' maintenance organization using approved methods.
Conclusions
The investigation concluded that the aircraft returned due to a technical reason, although according to the flight manual, flight could have continued normally despite the engine vibrations. The detachment of coating from the fan blade caused an imbalance that was detected by vibration sensors. No vibration limits are defined by the engine manufacturer for flight conditions other than takeoff.
No safety recommendations were issued in this preliminary investigation.