US Marine Corps Osprey aircraft have been involved in a series of accidents.
Last September, 2 service members were injured in a crash in Syria. In December 2016, one of the tilt-rotor aircraft broke up during a midair refueling drill off Okinawa, southern Japan.
Japan's Defense Ministry has obtained records of mishaps resulting in death or major damage involving Marine Ospreys.
They show that these "Class A" accidents occurred at an increasing rate of 3.24 per 100,000 flight hours as of the end of September 2017.
The figure rose from 1.65 in September 2012 -- when Ospreys were first deployed to Okinawa -- to 2.62 in 2016.
The figure is higher than the overall accident rate for all US Marine Corps aircraft, which stood at 2.72 as of the end of last September.
In January, the Osprey unit commander at Futenma Air Station in Okinawa was dismissed. The US Marines cited a loss of trust in the officer's ability to command.
They also say they're working to improve pilot training methods.