“Ultimately, the investigation determined that the aircraft did not suffer from any mechanical or material failures,” says Lt. Gen. Robert Schmidle, deputy commandant of Marine Corps Aviation. “There were no issues with the safety of the aircraft,” he told reporters at the Pentagon. He was answering questions about the findings about an investigation into cause of the crash, as all eyes are on the tilt-rotor transport slated to begin service at Futenma Marine Corps Air Station in October. That move is being opposed by Okinawa.

The official investigation report noted the aircraft in the April 11th crash had been taking off into heavy headwinds when, in an effort to avoid flying over tents set up for the exercise, the copilot made a 180-degree turn. He lost control during the transition to regular flight, the report says, and crashed from a high of about 14 meters. A major factor in the crash, says the report, was “lack of understanding of the true wind speed”.

A recommendation from the investigators has been that Osprey field manuals be updated to include more detailed information about how to best transition from vertical-helicopter-like take off to regular flight when there’s a tail wind.

Meanwhile, General James Amos, the top uniformed officer in the Marine Corps, says he’s ordering the MV-22 Osprey flights over heavily populated parts of Japan to be curbed as a safety issue. Amos says he’s working with Japan to reduce fears of the hybrid transport plan. He and Secretary of Defense Leon Panetta say they’ll not allow the Osprey to become operational in Japan until Japan’s government has ‘reconfirmed’ safety issues.

The first 12 MV-22 Ospreys destined for Okinawa are currently sitting at Iwakuni Marine Corps Air Station in mainland Japan. For the moment, they remain grounded.