The remains of one U.S. airman were recovered Wednesday after an Air Force CV-22B Osprey crashed off the coast of Japan, but seven others who were aboard the aircraft remain missing, the Air Force reported on Friday. 

“Seven Airmen are in DUSTWUN status meaning ‘duty status-whereabouts unknown,’” a release on Friday from Air Force Special Operations Command said. “At this time, we can confirm one set of remains has been recovered.”

Search and rescue efforts were continuing Friday in the area, and included a large number of U.S. military personnel and assistance from the Japanese government.

Flight operations of the unit to which the downed aircraft belonged are currently shut down, and all  V-22 Ospreys in Japan are receiving maintenance and safety checks, Deputy Pentagon Press Secretary Sabrina Singh said Friday.

"Timely and transparent"

“We have already started sharing information about the accident with our Japanese partners, and have pledged to continue to do so in a timely and transparent manner,” Singh added.

The aircraft was on a training mission when it crashed, and the cause of the crash is not yet known as an investigation continues.

Singh said Friday the “safety of our service members and Japanese communities is a top priority for the United States.”

“The United States is taking all appropriate safety measures, as we do for every flight and every operation,” she said.

Problematic aircraft?

Osprey aircraft have been involved in a series of fatal accidents in the last three decades, CNN reported.

The accidents have killed dozens of U.S. airmen over the 30-year history of the aircraft, both in training missions and while engaged in official actions, according to the Air Force Times.

There have been four fatal crashes involving Ospreys in the last two years, with 13 service members having been killed.

Ospreys fly faster than other types of helicopters, which allows them to surprise other aircraft in combat and transport wounded soldiers faster than their counterparts.

There are hundreds of Ospreys in operation as part of the U.S. military, mostly by the Marines and Air Force. Japan also operates Ospreys as part of its military operations.

The helicopters can hold up to three dozen crew members or up to 10,000 pounds of cargo, and cost about $90 million each.