The National Transportation Safety Board has concluded that a fatal tour helicopter crash last year on Kaua'i was caused by a manufacturing defect in a tail rotor fitting.

The March 11, 2007, crash of an Inter-Island Helicopters McDonnell Douglas 369FF helicopter in Ha'ena killed Michael Gershon, 60, of Walnut Creek, Calif., and seriously injured three other passengers.

Two of the passengers, Douglas Barton and wife Judy Barton, of Newport, N.H., in June announced a $9.5 million settlement in their lawsuit against Boeing Co., which merged with McDonnell Douglas in 1997; Aluminum Precision Products Inc., manufacturer of the defective fitting; and Smoky Mountain Helicopters, the company that operates Inter-Island Helicopters.

An NTSB probable cause report released yesterday said the defect resulted in separation of the tail rotor system and loss of tail rotor control. A contributing factor in the crash was the helicopter's impact with trees as it spiraled down for a crash-landing at the YMCA's Camp Naue, the report said.

Inter-Island Helicopters owner Ken D'Attilio said yesterday "there was nothing any of my mechanics or pilots could have done that would have prevented this, because the crack started from the inside out and was not visible to anyone."

"It was one of those tragic things. I don't see how it could have been prevented."

The flight had departed the Port Allen Airport on a 55-minute sightseeing tour. Pilot Donald Torres, 30, told investigators that about halfway through the flight, while soaring 1,000 feet above ground over Tunnel Beach, he heard two loud "bangs." The nose of the helicopter pitched down and the aircraft yawed to the right, the NTSB report said.

Torres said he recognized the YMCA property and decided to execute an autorotation to the open field at the campground.

A witness on the ground said she heard a loud "pop" and saw two objects fall from the helicopter into the ocean.

Police scuba divers searched for pieces to the tail rotor assembly for two days, but were unable to locate the missing parts. However, within weeks the parts were retrieved from the water by beachgoers and sent to the NTSB Materials Laboratory.

Closer examination of the parts revealed that the tail rotor blade assembly was fractured through the root fitting in the general area that coincided with a hole for the rotor blade retention bolt.

In response to the finding, the Federal Aviation Administration issued an emergency airworthiness directive on April 27, 2007, mandating inspection of the root fittings on certain MD 369 helicopters.

The same defect was later found in two helicopters operating in New Zealand.

The Ha'ena crash occurred three days after a Heli-USA Airways tour helicopter crashed at Princeville Airport, killing the pilot and three passengers.

The NTSB has not released its final report on the Princeville incident, which involved an Aerospatiale AS350BA helicopter.