WASHINGTON (AP) — A Marine Corps investigation has concluded that operator error caused the deadly April crash of an MV-22 Osprey aircraft in Morocco — an incident that has fueled unease in Japan, where the hybrid aircraft are being deployed.

In a report obtained Thursday by The Associated Press, the Marine Corps ruled out mechanical and safety problems with the tilt-rotor Osprey, which takes off like a helicopter and flies like an airplane. The report said high winds and failure to follow proper flight procedures were two significant factors in the crash.