The U.S. Marine Corps said Monday that pilot error was the main cause of the fatal crash of an MV-22 tilt-rotor aircraft in Hawaii in 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, according to U.S. Marine Corps Forces, Pacific.
The safety operation of the aircraft dubbed Osprey has been a matter of concern not only in the United States but also in Japan, where the U.S. military already deployed 24 units to its base in a densely populated area in Okinawa. The Self-Defense Forces plan to procure 17 units 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.
It said that sand and dust kicked up as the aircraft was hovering near the ground caused a stall in the left engine and resulted in a hard landing, which killed two crew members.