The arrival of the first group of MV-22 Osprey aircraft in Japan last week amid strong safety concerns means the central government has effectively committed itself to preventing accidents far into the future.
The safety of the U.S. tilt-rotor transports, deployed for actual operations less than five years ago, has yet to be fully established.
Still, once Ospreys are based at U.S. Marine Corps Air Station Futenma in Okinawa later this year as planned, they will fly over most of Japan. In addition, U.S. military helicopters are usually operated for some 40 years after deployment.
When U.S. Secretary of State Hillary Rodham Clinton visited Japan in early July, she stressed that the MV-22 Osprey has an “excellent” safety record.
According to released U.S. military data, however, the rate of Class-A flight accidents involving the Osprey that caused death or property damage worth $2 million or more stood at 1.93 per 100,000 flight hours as of April, against 1.11 for the U.S. CH-46 helicopter currently in service at the Futenma base.
From the development stage, skeptics have questioned the ability of the MV-22 Osprey to survive an emergency landing.
Defense Ministry officials maintain that if the two engines of the aircraft fail, it can make an emergency landing by means of autorotation, in which the act of descending sends air flowing through the rotor blades and makes them spin, or by shifting to the fixed-wing mode for a steep glide, also as the airflow turns the rotors.
But the MV-22 may not receive sufficient lift from autorotation, as its blades are smaller in diameter than those of a helicopter. In the Osprey Guidebook, the U.S. Marine Corps says the aircraft does not rely on autorotation for emergency landings, contradicting the Defense Ministry.
U.S. Deputy Secretary of Defense Ashton Carter said July 20 while in Japan that the Okinawa Osprey deployment is needed to maintain the deterrent power of U.S. forces. Clinton also said Japan’s defense capability will be enhanced by the move.
The Osprey has a flight range of 3,900 km, about 5.5 times more than the CH-46 helicopter it will replace at Futenma, and it can be refueled in flight.
Defense Minister Satoshi Morimoto has effectively thrown his support behind the deployment plan. “We cannot allow cracks in the deterrent power (of the U.S. forces)” by halting the planned deployment of the Ospreys, Morimoto said on TV July 22.