Possible Defect Grounds Navy, Marine Copters

The Marine Corps and Navy announced Monday 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. Long considered a work horse for the military, the Vietnam era helicopter is used to transport troops and supplies.

The grounding order came 10 days after a Sea Knight 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 had fatal accidents in the past, 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 flown by the Navy.

However, since 1980, more than 30 Marines around the world have died in Sea Knight accidents. The most serious occurred in the Atlantic in 1986 when a crash killed 15 Marines.

An investigation into the potential 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 where the helicopter’s squadrons are based, such as the U.S. Marine Corps Helicopter Air Station in Tustin in Orange County.

“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 North Island Naval Station on Coronado Island are not the most used aircraft and the Navy will rely on other helicopters, spokesman Fred Wilson said.

In the May 4 incident, the Sea Knight made a hard landing in the desert at the Marine Air Ground Combat Center in Twentynine Palms while participating in a warfare exercise.

The military believes the accident was caused by a problem in the rotor and transmission of the Tustin-based helicopter.

“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.”

Before this month, the last crash involving the Sea Knight was in March, 1988, at Camp Pendleton. Four Marines were injured.

The 15,000-pound Sea Knight has a three-man crew and can carry 17 men. The helicopter, which boasts a maximum speed of 166 m.p.h., is a twin-engine tandem-rotor craft. It has a rear landing ramp that allows rapid loading and unloading of cargo and supplies. An external hook also allows the aircraft to carry loads beneath its belly.

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