Possible Defect Grounds Navy, Marine Copters

The Marine Corps and Navy Monday announced suspension of all flight operations worldwide by CH-46 Sea Knight helicopters because of a possible mechanical defect.

The move effectively grounds 342 helicopters--261 used by the Marines and 81 by the Navy. Sixty of the aircraft are based at the Tustin U.S. Marine Corps Helicopter Air Station, a major Sea Knight base. The Vietnam-era helicopter, long considered a workhorse for the military, is used to transport troops and supplies.

The grounding order came 10 days after a Sea Knight based in Tustin made a “hard landing” in the California desert, injuring the 17 Marines aboard, the Navy said Monday. Senior Navy officers in Washington said the helicopters were grounded because of a transmission problem that could lead to a loss of power to the rear rotor.

Although the CH-46 has been involved in fatal accidents, it is considered one of the military’s most reliable. In 1984, Aviation Week & Space Technology magazine listed it as having one of the lowest accident rates of aircraft the Navy flies.

However, more than 30 Marines around the world have died in Sea Knight accidents since 1980. The most serious occurred in the Atlantic in 1986, where a crash killed 15 Marines. A number of Marines based in Orange County have been killed in Sea Knight crashes. The most recent incident involved two from the El Toro Marine Corps Station who died in May, 1989, when their craft collided with another helicopter near Reno. Four Tustin-based Marines were killed in March, 1989, when their Sea Knight crashed in South Korea.

Locally, the most recent reported crash of a Sea Knight was at Camp Pendleton in March, 1988; four Tustin Marines were injured.

An investigation into the possibility of mechanical problems is expected to take several weeks to complete, a Navy spokesman said.

“Whenever you ground a fleet of aircraft, it’s not something you do on a whim,” said Senior Chief Petty Officer Bob Howard, a Pacific Fleet spokesman in San Diego. “It’s a very serious thing. But the most important thing is the safety of the crew.”

The grounding will have a major effect everywhere the helicopter’s squadrons are based. “We have other helicopters, but the Sea Knight is our main assault helicopter,” said Marine Lt. Gene Browne, a spokesman for the squadrons. “This is going to have a serious impact on flight operations.”

The 35 Sea Knights based at the North Island Naval Station on Coronado Island are not the most used aircraft, spokesman Fred Wilson said, and the Navy will rely on other helicopters.

In the May 4 incident, the Sea Knight made a hard landing while participating in a warfare exercise in the desert at the Marine Air Ground Combat Center in Twentynine Palms. The three crew members belonged to the 3rd Marine Aircraft Wing headquartered in Tustin; the others on board were from Camp Pendleton.

The military believes that the cause of the accident was a problem in the rotor and transmission the craft.

“We were lucky with the last one that there were no fatalities. What we are trying to avoid is being not so lucky the next time,” Browne said. “This is basically a precautionary measure. You’ve got problems that are inherent to one aircraft . . , so if we need to ground the aircraft to find out, it’s an inconvenience; but the lives are more important.”

The twin-engine tandem-rotor Sea Knight operates with a three-man crew and can carry 17 men. It weighs 15,000 pounds, can attain a maximum speed of 166 m.p.h., and has a rear landing ramp that allows rapid loading and unloading of cargo and supplies. It also has an external hook to carry loads beneath its belly.

The aircraft was first built by Boeing Vertol Co. of Philadelphia in 1965.