A LOT Polish Airlines Boeing 787-800, registration SP-LRG performing flight LO-91 from Warsaw (Poland) to Beijing (China), was en route at FL390 about 200nm north of Omsk (Russia) when the crew decided to return to Warsaw due to indications of engine (Trent 1000) vibrations.
The aircraft descended to FL380 for the way back and landed safely on Warsaw’s runway 33 about 4 hours after the decision to return.