The U.S. Marine Corps said pilot error was the main cause of the fatal crash of an MV-22 Osprey tilt-rotor aircraft in Hawaii last May.
"The investigation found the main contributing factors to this mishap were pilot performance and an improper site survey" of the landing zone in a training area on Oahu Island, the U.S. Marine Corps Forces, Pacific, said Monday.
The safety of Ospreys has been a matter of concern not only in the United States but also in Japan, where the U.S. military has already deployed 24 to the Futenma base located in a densely populated area in Ginowan, Okinawa Prefecture.
The Self-Defense Forces plan to procure 17 of the aircraft by the end of March 2019.
"The pilots did not violate any regulations or flight standards," but they should have taken into account factors such as low visibility in the landing zone and chosen a different route and place, the Marine Corps said.
Sand and dust kicked up as the aircraft hovered near the ground caused the left engine to stall and resulted in a hard landing, which killed two crew members, the military said.
After being briefed on the finding by Brig. Gen. Christopher Mahoney, deputy commander of Marine Corps Forces, Pacific, in the suburbs of Honolulu, Defense Minister Gen Nakatani told reporters that the government will proceed with the planned Osprey procurement for the Ground Self-Defense Force.
"I understand Ospreys do not have structural flaws," Nakatani said. He urged Mahoney to ensure safety of the aircraft as civilians in Japan, particularly in Okinawa, have concerns about it.