On Dec. 19, six days after a U.S. Marine Corps MV-22 Osprey crash-landed in the sea off Okinawa Prefecture, U.S. Air Force Lt. Gen. Jerry Martinez, commander of U.S. Forces Japan, issued a statement suggesting a refueling "mishap" and not any problem with the aircraft itself had caused the accident.
"We have conducted a thorough, careful and exhaustive review of MV-22 aviation safety procedures and briefed Ministry of Defense and Ministry of Foreign Affairs officials," Martinez's statement read. "While the investigation is ongoing, we are highly confident in our assessment that the cause of the mishap was due solely to the aircraft's rotor blades coming into contact with the refueling line."
According to information from the U.S. military released by the Defense Ministry, on the night of Dec. 13, the Osprey in question was conducting in-flight refueling training with an MC-130 special mission aircraft several dozen kilometers from the Okinawa main island. Though there were heavy winds, the training was still possible. At around 9:05 p.m., turbulence and other factors caused one of the Osprey's propellers to clip the MC-130's refueling hose after detaching. The damage became worse, and the Osprey lost stability. It crash-landed in shallow waters off Okinawa about 25 minutes later.
The Defense Ministry stated that it "recognizes the reasonableness" of the U.S. military's explanation, though it continued to be evasive over the details of the accident. The reason for this is that the ministry simply hasn't been given that detail by the U.S. military, including whether the "turbulence" affected the Osprey or the MC-130 and the exact nature of the damage to the propeller.
The 11th Regional Coast Guard Headquarters in Naha has opened an investigation into the accident for possible violations of the Act on Punishment of Acts to Endanger Aviation and has requested the cooperation of the U.S. military. However, as of Dec. 19, the Coast Guard had not received a reply. The U.S. military is apparently conducting the wreckage recovery and interviews with the Osprey pilot.
Under a document related to the Japan-U.S. Status of Forces Agreement, Japanese authorities have no right to search or seize U.S. military "property" without the agreement of U.S. forces, making it difficult for Japanese investigators to clarify the cause of the accident.
According to former air accident investigator Koichi Saito, it is "premature" to allow the Ospreys in Japan back into the air. "Ospreys are special aircraft that have both a helicopter mode and a fixed-wing mode. It's still unknown whether the aircraft can switch between its two modes if it has a damaged propeller blade," he continued.
There are 24 MV-22 Ospreys based at U.S. Marine Corps Air Station Futenma in Ginowan, Okinawa Prefecture, and they also conduct flights in the Kanto region including from Yokota Air Base. Furthermore, Japan's Ground Self-Defense Force is scheduled to take delivery of 17 Ospreys by fiscal 2018, with deployment to Saga Airport set for fiscal 2019. However, related local governments are growing increasingly uneasy, and a senior Self-Defense Forces officer told the Mainichi Shimbun that the Okinawa Osprey accident "is likely to have repercussions for how we explain the deployment to locals."
Saga Gov. Yoshinori Yamaguchi told the press corps on Dec. 19, "I asked that the cause of the accident be thoroughly investigated. I thought there would be a proper response, so the (Ospreys') resumption of flights seems sudden.