RIVERSIDE, Calif. — A U.S. Air Force pilot from Riverside was among eight men killed when a CV-22 Osprey crashed while on a training mission off the southern coast of Japan, the U.S. Department of Defense confirmed Dec. 5.

Maj. Luke A. Unrath, 34, was fatally injured Nov. 29 when the tilt-rotor Osprey plunged into the sea around Yakushima Island.

His remains were recovered during a joint rescue and recovery operation conducted by the Air Force, Japan Coast Guard and fishermen, Pentagon officials said.

At least three of the eight victims are still unaccounted for, and recovery efforts were ongoing this week.

Background information on Unrath, including the flight commander’s service record, wasn’t immediately available.

The cause of the crash was under investigation.

The specific mission of the Osprey crew wasn’t disclosed, but was described by the Pentagon as routine.

It was the first crash involving a CV-22 operated by the Air Force.

The aircraft made its debut with the U.S. Marine Corps more than 30 years ago.

The tilt-rotor departs and lands in a vertical profile, like a helicopter, but the propulsion units can be re-directed forward to enable flying it like a twin-engine fixed-wing airplane.

It has had a checkered history, with multiple fatal crashes. According to the Air Force Times, the Osprey fleet has come under scrutiny recently for so-called “hard clutch engagements,” in which the aircraft suffer temporarily slips that cause power imbalances in the rotors, making them “lurch dangerously.”