WASHINGTON (AP) — Japan has grounded its fleet of V-22 Osprey planes again after an incident last Sunday in which one of the hybrid helicopter-planes unexpectedly banked and hit the ground while trying to take off.

The V-22 was participating in the joint US military exercise Keen Sword and was carrying 16 passengers, including three US service members. During take-off, “it became unstable as it rocked from side to side and the left wing, the lower part of the aircraft came into contact with the ground and part of the aircraft was damaged, so the flight was aborted Japan’s Ground Self Defense said. The force said in a statement.

It was the first major incident involving Japan’s V-22 fleet since the US Air Force Special Operations Command crashed off the coast of Japan last November. killed eight service members and resulted in a fleet-wide moon landing for both Japan and the US

The aircraft resumed flight operations earlier this year, but the use of the Osprey remains controversial particularly in Okinawa, where residents have questioned its safety.

The Osprey in last Sunday’s incident was able to land and no one was injured, but Japan will keep its fleet of more than a dozen V-22s on the ground while it investigates the incident, Defense Minister Gen. Nakatani told reporters last week.

“We believe there is no safety issue with the Ospreys, although ensuring flight safety is a prerequisite for aircraft operations,” Nakatani said.

The Pentagon’s V-22 Joint Program Office is supporting Japan’s investigation into the incident, spokesman Neil Lobeda said Saturday.

V-22s were operating on the Japanese island of Yonaguni during joint exercise Keen Sword. Yonaguni is only 100 kilometers (62 miles) east of Taiwan.

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Yamaguchi reported from Tokyo

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