17 Marines Hurt in Helicopter Accident : Military: The Tustin-based craft made a “hard landing” during training exercises at Twentynine Palms.

A helicopter based at the Marine Corps Air Station in Tustin made a “hard landing” during desert training exercises Friday, injuring all 17 Marines on board, officials said. None of the Marines were listed in serious condition.

Although the extent of injuries was not released, officials said three Marines had serious enough injuries that they were flown to the naval hospital at Camp Pendleton for treatment. Twelve of the Marines were still undergoing medical examinations late Friday night at the naval hospital in Twentynine Palms.

Two Marines were released back to their duties after treatment, Capt. Timothy Hoyle said.

The accident occurred about 2:15 p.m. at the Marine Air Ground Combat Center at Twentynine Palms in San Bernardino County when the CH-46E Sea Knight helicopter made a “hard landing,” Hoyle said.

The cause of the accident is under investigation, he said.

At the time of the accident, the helicopter was “participating in a combined arms training exercise,” Hoyle said.

No other details about the exercise were released.

Aboard the craft were 14 infantrymen from Company E, 2nd Battalion, 9th Marine Regiment, 1st Marine Division, which is based at Camp Pendleton.

The helicopter and its three crewmen belong to the 3rd Marine Aircraft Wing, headquartered at the Marine base in Tustin.

The Sea Knight is considered the workhorse of the Marine helicopter force and has been in service since 1965. It is used by the Marines mostly as a troop mover.

The aircraft is made by Boeing Vertol Co. of Philadelphia and is generally praised for its safety record. In 1984, the CH-46 was listed by Aviation Week & Space Technology magazine as having one of the lowest accident rates of any aircraft flown by the Navy.

The last reported local crash of a Sea Knight was in March, 1988, at Camp Pendleton; four Marines were injured.

Since 1980, more than 30 Marines around the world have been killed in CH-46 accidents. The most serious of those accidents occurred in 1986 when 15 Marines were killed when their Sea Knight crashed into the Atlantic Ocean.

In 1987, the helicopter was hit by a string of accidents, in which eight Marines were killed and 22 were injured. Seven of the eight Marines killed were flying in helicopters at night when the pilots were wearing night-vision goggles, which have been under fire in some quarters as being unsafe.

Times staff writer Shelby Grad contributed to this report.