LIHU'E, Kaua'i — Crash investigators have taken custody of a tail rotor blade from the March 11 crash of an Inter-Island Helicopters tour helicopter at Ha'ena that killed one person.

National Transportation Safety Board air safety investigator Jim Silliman confirmed that the blade, which washed up on the beach at Ha'ena during the past week, has been shipped to the NTSB laboratory in Washington, D.C.

It is potentially a key piece of evidence, since it could help explain why the helicopter crashed.

The Hughes 500 tour aircraft went down from a cruising altitude of about 1,500 feet after the pilot and people on the ground heard two distinct bangs, Silliman said. Witnesses on the ground said that when they looked up, they saw two pieces falling from the helicopter, which had started to spin. One piece fell fast, and the other fluttered to the water below.

One man was killed and three other passengers injured.

A survey of the wreckage later showed that the entire tail rotor section, including the rotor blades, part of the rear gearbox and output shaft, were missing from the aircraft.

Pilot Donald Torres, 30, of Hanapepe, managed to get the crippled helicopter to the ground at the YMCA's Camp Naue, but clipped trees and a fence at the edge of the camp's open lawn. The helicopter fell on its right side. Torres was able to walk away from the crash.

In his preliminary report, Silliman said the review of the parts that went down with the aircraft showed evidence of extreme stress, but that there was no indication of the cause of the problem — whether something hit the rotors or whether something mechanical failed, causing the rotor section to blow apart.

"The tail rotor gearbox was sent to the National Transportation Safety Board's Materials Laboratory for inspection," Silliman said. "The initial inspection of the tail rotor gearbox on March 22, 2007, revealed that all the fractures were typical of overstress fractures. A portion of the tail rotor gearbox housing was missing along with the tail rotor output shaft and tail rotor blades."

In past crashes in which tail rotors blew apart, evidence on the rotor has indicated a cause of the crash.

It is not yet known whether the single rotor will be enough to clear up the mystery, and Silliman said finding the remaining parts is important. Rough surf conditions have made it difficult to dive the waters off Ha'ena. Silliman said that if anyone does find the missing parts of the tour helicopter, they can be washed off with fresh water and turned over to Kaua'i police.

Michael Gershon, 60, of Walnut Creek, Calif., died in the crash. Injured were Dania Hansen, 60, of Los Altos, Calif., and Douglas Barton, 60, and his wife, Judy Barton, 51, of Newport, N.H.

A separate NTSB investigation continues in the crash three days earlier at Princeville, Kaua'i, of an AStar tour helicopter operated by Heli USA. Four people were killed and three injured in that crash.

Reach Jan TenBruggencate at jant@honoluluadvertiser.com.