"Two US military Osprey transport aircraft made unusual landings at an airport in northeastern Japan on Monday. One of them reportedly detected trouble during flight. The CV-22 transport planes from the Yokota Air Base in Tokyo landed in succession at Yamagata Airport on Monday afternoon. The Japanese Defense Ministry's regional bureau says it was told by the US military that the planes made "precautionary landings" after one of them detected trouble. A maintenance crew from the Yokota base is due to arrive on Tuesday to check the plane. The other Osprey has already left the airport. The US military is due to investigate the cause of the trouble."

https://www3.nhk.or.jp/nhkworld/en/news/20210615_11/