The head of Heli USA Airways is disputing National Transportation Safety Board findings that fault the company's mechanics for a March 8, 2007, tour helicopter crash on Kaua'i that killed four people and seriously injured three others.

Heli USA president and CEO Nigel Turner said yesterday the root cause of the tragedy can be traced to problems with the hydraulic system on Aerospatiale/Eurocopter AS350 helicopters manufactured by Eurocopter.

"My concern is there are a lot of problems with the hydraulic system on the helicopter, and what the NTSB should be doing is looking at how we can make this safer instead of blaming mechanics," Turner said.

An NTSB report released yesterday said improper tightening of a bolt connecting the servo, a flight control device, as well as the installation of a severely worn lock washer allowed the servo to disengage from its mount, leading to a complete loss of control as the A Star helicopter was moments from landing at Princeville Airport.

The agency cited as a contributing factor the company's failure to make sure its maintenance program complied with federal regulations.

Pilot Joseph Sulak, 59, was killed, along with passengers John O'Donnell, 45, of East Rockaway, N.Y., Margriet Inglebrecht, 19, of Santa Maria, Calif., and Teri McCarty, 47, of Cabot, Ark.

The NTSB said the manufacturer issued a bulletin recommending a lower torque value, or level of tightening, for an upper clevis locking nut securing the servo to prevent cracking in the servo body. A Heli USA mechanic mistakenly used the reduced torque value to tighten a lower bolt instead of a higher value prescribed by the manufacturer, the report said.

Turner said the company mechanic shouldn't be faulted because the manufacturer has since issued a new directive that the same reduced torque value be used for both bolts.

"What's ironic is that since the accident, the manufacturer actually reduced it to the same torque value as the top bolt. Even though our mechanic was incorrect at the time of the installation of the servo, it's irrelevant because they have reduced the lower bolt value to 169 inch-pounds," same as for the upper bolt, Turner said.

The NTSB also reported that none of the Heli USA mechanics at the Kaua'i station had received factory training, and that their maintenance manuals were out of date.

"The NTSB are incorrect about lack of factory training. Our chief of maintenance in Hawai'i did receive factory training on the A Star. He, in turn, trained other mechanics at the base. This is normal practice and conforms to (Federal Aviation Administration) requirements," Turner said. "The mechanic who worked on the servo has about 20 years working on the A Star helicopter, was current for all FAA requirements, and had done this job on the servo many times and was well qualified to do this."

After the Princeville crash and five other incidents involving the same type of aircraft, the NTSB last year recommended additional inspections of Eurocopter AS350 hydraulic system components.

Heli USA also operates tour flights on O'ahu and at Las Vegas and the Grand Canyon.