TOKYO — The U.S. military said Wednesday that it was grounding all of its Osprey V-22 helicopters, a week after one of the aircraft crashed off the coast of Japan, killing all eight U.S. airmen aboard.
A preliminary investigation of the crash of the CV-22B Osprey off the Japanese island of Yakushima on Nov. 29 indicates that it may have been caused by a materiel failure, the Air Force Special Operations Command said in a statement, meaning the problem was with the aircraft rather than crew member error. The underlying cause of the failure remains unknown.
The crash in Japan is the latest to raise safety questions about the Osprey, an American hybrid aircraft that has been involved in multiple fatal accidents.
Lt. Gen. Tony Bauernfeind, head of Air Force Special Operations Command, has ordered an operational stand-down of the Air Force CV-22 fleet “to mitigate risk while the investigation continues.”
“The standdown will provide time and space for a thorough investigation to determine causal factors and recommendations to ensure the Air Force CV-22 fleet to return to flight operations,” the statement said.
The Naval Air Systems Command, which is responsible for both Marine Corps and Navy variants of the aircraft, said in a separate statement that it was grounding all V-22 Ospreys “out of an abundance of caution.”
The groundings affect hundreds of aircraft, according to The Associated Press, including 51 from Air Force Special Operations Command, 27 from the Navy and as many as 400 from the Marine Corps.
An Air Force official told NBC News it was unclear how long the stand-down would last, but that the Ospreys would not return to the skies until they were deemed safe to fly.
The remains of a U.S. Osprey aircraft that crashed off the Japanese island of Yakushima on Nov. 29.Japan’s 10th Regional Coast Guard/Jiji Press via AFP – Getty Images
Japan, a U.S. treaty ally and the first foreign country to own and operate the aircraft, grounded its 14 Ospreys after the crash “until circumstances surrounding the accident become clear,” asking U.S. forces to do the same.
“It goes without saying that ensuring flight safety is the highest priority in operating an aircraft,” Chief Cabinet Secretary Hirokazu Matsuno, Japan’s top government spokesperson, told reporters on Thursday. “As the Osprey is also being operated by the Self-Defense Forces, we will continue to request the U.S. side to share information in order to ensure their safety.”
The Osprey, which takes off, lands and hovers like a helicopter but flies like a fixed-wing plane, has had a troubled history, with more than 60 people killed in accidents since the early 1990s.
Officials are still investigating an Osprey crash in Australia in August that killed three of 23 U.S. Marines on board.
Arata Yamamoto reported from Tokyo, Larissa Gao from Hong Kong and Mosheh Gains from Washington.
Arata Yamamoto
Arata Yamamoto has been a NBC News producer in Tokyo since 1993.
Larissa Gao
Larissa Gao is a fellow on NBC’s Asia Desk, based in Hong Kong.
Mosheh Gains
Mosheh Gains is a Pentagon producer for NBC News.
The Associated Presscontributed.