タービン羽根ちぎれ破損か　熊本日航機金属片落下―運輸安全委

　熊本県上空を飛行中だった日本航空機（ボーイング７６７―３００型）の左エンジンに２０１８年５月、不具合が発生し金属片が多数落下したトラブルで、運輸安全委員会は３０日、高圧タービンで高速回転するブレードと呼ばれる約１５センチの金属製の羽根１枚がちぎれたことで、エンジン部品が連鎖的に破壊されたことが原因と推定する報告書を公表した。落下した金属片は計約７３キロとみられる。
　運輸安全委によると、高温による腐食が進み、ブレード台座内側に施されていたコーティング層に亀裂が生じていた。１万５０００回を超える離着陸による金属疲労などで、ブレード本体にも亀裂が入り、ちぎれたとみられる。ブレードの破片で奥にある低圧タービンの大部分も損傷した。（2020/07/30-10:42）

An incident in which metal fragments fell from a Japan Airlines flight in 2018 was likely caused by a blade of a high-pressure turbine tearing off and damaging engine parts as a result, a Japanese transport ministry panel said in a report Thursday.
   The 15-centimeter-long metallic blade was torn off the turbine in the left engine of the Boeing 767-300 jet while it was flying over the town of Mashiki in the southwestern Japan prefecture of Kumamoto on May 24, 2018, resulting in a total of some 73 kilograms of metal fragments falling to the ground, according to the report.
   The board discovered cracks in a layer of coating inside of the blade base due to corrosion caused by high temperatures. The blade itself likely had cracks due to metal fatigue after the airplane experienced over 15,000 takeoffs and landings. Large parts of the low-pressure turbine in the engine were also damaged by the blade fragments.
   A turbine blade tear was also the cause of an incident in which the right engine of a plane of the same model caught fire in December 2005.
   No one was injured in the 2018 incident, which took shortly after the JAL jet took off from Kumamoto Airport. But damage was caused to properties, including cracks in windows at a hospital. Some 400 pieces of metal fragments related to the incident were collected.