The Defense Ministry on Tuesday concluded that pilot error caused the fatal crash of an MV-22 Osprey in Morocco in April, an accident that set off a strong outcry against the deployment of the airplane-helicopter hybrid in Japan.

A 15-member expert panel launched by the ministry in July confirmed a U.S. Marine Corps report earlier this month that ruled out mechanical error and safety problems with the Osprey itself, marking a step forward in the planned deployment of the transport aircraft in Okinawa in October.

“The accident is largely attributable to the blatant breach of the manual by the copilot,” said Tetsuro Kuroe, deputy director general of the ministry’s Bureau of Defense Policy Bureau and head of the investigation panel.

According to the ministry’s report released Tuesday, the copilot, who had control of the craft at the time of the crash, was not aware of strong winds in the area measuring 15 to 27 knots (27.78 to 50 kph), which tilted the aircraft forward while it was in helicopter mode.

The aircraft’s manual, called NATOP, or Naval Air Training and Operating Procedures Standardization, forbids allowing the Osprey to hover in wind speeds of 15 to 27 knots.

The copilot also violated the manual by tilting the engine nacelles too far forward before the speed of the aircraft reached 40 knots (74 kph). The nacelles are the engine housings on each wing tip, and rotating them converts the aircraft from helicopter to airplane mode or vice versa.

The manual prohibits this operation in order to keep the aircraft from taking an acute angle as well as preventing it from losing lift.

Kuroe, who monitored an Osprey simulation when he was briefed on the report in the U.S. earlier this month, said the aircraft’s operation is largely controlled by an onboard computer system, which allows the pilot to conduct risky operations only in rare instances. Neither the Defense Ministry nor the U.S. Marine Corps have yet to find out why the copilot ignored the manual.

The ministry also agreed with the marines that the errors can be blamed on the copilot’s lack of experience and limited flight hours. The copilot had flown the Osprey about 160 hours. By comparison, copilots in the Self-Defense Forces have an average of 400 to 600 hours of flight time in their aircraft.

One difference between the Defense Ministry’s report and that of the marines was that the ministry also holds the pilot accountable for the crash, as it believes the pilot’s lack of proper instruction or oversight when the copilot made operational errors may have contributed to the crash.

Defense Minister Satoshi Morimoto is traveling to Okinawa Prefecture and Yamaguchi Prefecture on Wednesday and Thursday to explain the assessment of the U.S. investigative report in a bid to seek public understanding for upcoming Osprey flights. Twelve Ospreys are currently at the Iwakuni base in Yamaguchi and are to be safety-tested before deployment in Okinawa.

The safety of the aircraft will not be verified until Japan confirms the U.S. investigative report on the crash of a CV-22 Osprey in Florida, which is due by the end of this week. The U.S. Marine Corps has pledged to hold off on the Osprey test flights until Japan concludes there is no mechanical problems with the aircraft.

Amid the increasing public outcry against flying the aircraft in Japan, the government has been stepping up its efforts to appease concerns heightened by the two recent crashes, which sources in both the Japanese and U.S. government admit came at the worst possible time before the deployment.

In the beginning of August, Morimoto met with U.S. Defense Secretary Leon Panetta and took a test flight on an Osprey. In a rare move, the Defense Ministry is hosting a public symposium Wednesday, featuring U.S. experts, on the deployment of the Osprey and the Japan-U.S. alliance.

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