Japan's Defense Ministry has acknowledged that the rate of serious accidents involving the US Marines' Osprey aircraft has soared to a record high.
The ministry earlier made an inquiry to the US Defense Department on Class A mishaps involving the tilt-rotor aircraft. Such accidents have resulted in major damage to the aircraft or deaths.
The Defense Department says the rate of serious accidents is determined by the occurrence of such accidents per 100,000 flight hours. The number as of late September was 3.27, the highest known to Japanese Defense Ministry officials.
The officials began keeping records in 2012, when Ospreys were deployed at the US Marine Corps Futenma Air Station in the southernmost prefecture of Okinawa. The figure was 1.65 in September 2012 and 2.62 in 2016.
The accident rate of all aircraft operated by US Marines as of the end of September was 2.72.
Ministry officials say they view accident rates as one of a number of indexes. They say they find no safety problems with Ospreys and safe flights are possible.
Ospreys have been hit by Class A mishaps during the past 12 months. One was crippled in an emergency water landing in Okinawa last December. Others also crashed in Australia and Syria.