AUDREY McAVOY,

Associated Press

HONOLULU (AP) — One Marine is in critical condition and three others remain hospitalized in stable condition after a fatal MV-22 Osprey crash over the weekend, the Marine Corps said Monday.

Seventeen others treated for injuries have been released, the 15th Marine Expeditionary Unit said in a statement.

The next of kin of the one Marine who died have been notified, the Marines said. The Marine Corps won’t release the Marine’s identity until 24 hours after the notification.

The crash is under investigation.

The Osprey had a “hard landing mishap” during training Sunday at Bellows Air Force Station on Oahu, the Marines said. There were 21 Marines and one Navy corpsman on board.

Witnesses saw three Osprey aircraft flying together, and then one catch fire after crashing in an open field. They said black smoke was billowing from the fire.

The 15th Marine Expeditionary Unit is based at Camp Pendleton in California. It’s currently in Hawaii for about a week of training exercises.

The incident over the weekend wasn’t related to a symposium on amphibious landings involving defense leaders from 23 nations, which will include a demonstration of an amphibious landing at Bellows on Tuesday.

Ospreys may be equipped with radar, lasers and a missile defense system, and each can carry 24 Marines into combat.

Built by Boeing Co. and Bell, a unit of Textron Inc., the Osprey program was nearly scrapped after a history of mechanical failures and two test crashes that killed 23 Marines in 2000.

The aircraft have since been deployed to Iraq and Afghanistan. Some Osprey also are helping with earthquake-relief efforts in Nepal.