The workhorse of Hawai'i's air tour helicopter fleet — Eurocopter's AS-350 series of helicopters — is being recommended for additional inspections after six "events" since 2002, including a crash on Kaua'i last year that killed four people and left three with serious injuries.

The National Transportation Safety Board recommended that the Federal Aviation Administration:

• Require operators of AS-350 and its sister EC-130 helicopters to perform a wear check, visual inspection and lubrication of the hydraulic power assembly splines and coupling sleeve splines, and repeat the procedures at 100-hour intervals.

• Require manufacturer Eurocopter to identify hydraulic pump drive shafts and coupling splines that do not meet design specifications in its AS-350 and EC-130 helicopters and remove the parts from the supply chain.

"We take the NTSB's recommendations seriously," said FAA spokesman Ian Gregor. "We have 90 days to respond to the NTSB recommendations, and we will respond in that time frame."

The AS-350, or AStar, is popular with air tour helicopters and with law enforcement agencies, Gregor said.

In Hawai'i, "90 percent of the state uses AS-350s, maybe more than that," said Preston Myers, the owner of Safari Helicopters, who introduced air-conditioned AStars to Kaua'i in 1988. "It started off with me. Everybody was flying Jet Rangers. The AStar took hold. It has forward seating, no obstructions and comfort. It's smooth and quiet, and extremely comfortable."

Myers said he was the first in Hawai'i to call the AS-350 "the Cadillac of helicopters. That phrase has been copied somewhat and used by tour companies in the tourist magazines."

A few Hawai'i tour companies still fly versions of the egg-shaped Hughes 500 helicopters, Myers said, "but you can't look out forward from the back seats at all and you have a drive shaft right next to your ear, unlike the AStar, where there is no drive shaft inside."

The AStar's drive shaft and its hydraulic components were the focus of the NTSB report.

CRITICAL PARTS

The helicopter's hydraulic pump assembly is driven by a pulley assembly that contains a coupling sleeve, the NTSB said. The coupling sleeve, with internal splines, extends through the center of the pulley assembly to engage with the external splines on the hydraulic pump drive shaft.

"The helicopter can be flown without hydraulic power," the NTSB said, "… but doing so increases the physical demands on the pilot and can cause a serious accident."

Inspectors looked at parts of the helicopters from these accidents:

• March 8, 2007: Crash of a Heli USA AS-350 in Princeville, Kaua'i, that killed four people and left three seriously injured;

• Sept. 20, 2003: Crash of an AS-350 into the side of the Grand Canyon that killed seven;

• Sept. 11, 2002: Hard landing of an AS-350 that had no location given; and

• Three "run-on landings," which the NTSB described as precautionary landings "in situations that might include a hydraulic power failure where, due to the loss of power to the controls, the aircraft lands with some forward velocity and slides to a halt."

A FATAL FAILURE

Joe Sulak, the pilot of the Heli USA Airways' AS-350, was about two miles from Princeville last year, trying to return to the airport, when he reported a hydraulic system failure, just before crashing on a grassy area near a runway on the airport's northwest end.

Sulak and three of his passengers — one each from New York, California and Arkansas — were killed. Three others — also from New York, California and Arkansas — suffered serious injuries.

The NTSB inspected the crumpled AStar's hydraulic pump and pulley assembly and found that the drive shaft O-ring had not been installed, according to the NTSB report.

The drive shaft splines and coupling sleeve splines were relatively intact, but the "hardness" at the minimum depth for the drive shaft splines was significantly below requirements, the NTSB found. The grease in the coupling sleeve cavity also was dried and incapable of lubricating the splines.

Just 70 hours later, a Hughes 500 tour helicopter from competitor Inter-Island Helicopters crashed five miles from where the wreckage of the AS-350 still lay, killing one of the Hughes 500's four passengers.

The Eurocopter group was formed in 1992 from the merger of the helicopter divisions of French-based Aerospatiale-Matra and Germany's DaimlerChrysler Aerospace. The group is now a wholly owned subsidiary of EADS (European Aeronautic, Defense and Space Co.), which the company calls one of the three largest aerospace groups in the world.

Ross Scott, the owner of Hawai'i's Sunshine Helicopters, used to fly Bell Jet Rangers until he got his first ride in an AS-350 in 1989.

"There was no going back," Scott said. "I loved my Jet Ranger. It's a real pilot's machine. But the AS-350 was a no-brainer."

Instead of four passengers in the Jet Ranger — including two who had to face backward — the AS-350 can comfortably seat "four very large people in the back seat, and they're not crunched up against each other, plus two in the front with the pilot."

The even roomier EC-130 also features elevated rear seats, similar to theater-style seating.

"The 350 fits the bill," Scott said. "Everybody can see forward and sideways, with 180-degree views."

Sunshine now has a fleet of five EC-130s and five "BA" versions of the AS-350, which Scott is retrofitting with larger but more fuel-efficient engines that burn seven to eight gallons less per hour.

The new AS-350 "FX" versions offer "better power and better fuel efficiency that are also quieter because of a bigger tail rotor, plus a $30,000 air filter that quiets down the intake noise," Scott said. "We call it the green machine."

'A GOOD SAFETY RECORD'

In 24 years of flying, Scott's fleet of AStars and EC-130s have experienced five accidents and "incidents," but no deaths.

The most serious injury was a passenger's fractured wrist from a hard landing caused by pilot error, Scott said.

Three of the five incidents were the result of pilot error and two were mechanical problems.

None was the result of hydraulic problems, Scott said.

"We've flown over 850,000 passengers," he said. "I'd call that a good safety record."

In addition to daily pilot "walk-around" inspections looking for things such as leaks and signs of fatigue, "my maintenance looks at these helicopters every day," Scott said. "We're constantly inspecting."

So, like other Hawai'i tour helicopter owners, Scott said, he would welcome any additional inspections to ensure the AS-350 or EC-130s are safe.