The three passengers killed when their tour helicopter crashed on Kauai and the three survivors were from Arkansas, California and New York, authorities said Friday.
None of the victims' names or ages was released.
The helicopter went down at Princeville Airport on Thursday shortly after its Heli-USA Airways pilot radioed that he was having problems with the hydraulics.
Witnesses reported hearing a loud boom as far as a mile away and the sound of crunching metal as the helicopter hit the ground about 200 yards from its normal landing pad. Two men and two women died, three in the crash and one on the way to a hospital.
The three survivors were flown to Queen's Medical Center in Honolulu in critical condition. The pilot didn't survive, Kauai County spokeswoman Mary Daubert said.
On Friday, investigators from the Federal Aviation Administration and the National Transportation Safety Board headed to the crash scene to try to determine what went wrong.
FAA spokesman Ian Gregor said that the pilot had more than 10,000 hours flying an A-Star, the model that crashed. The craft itself had showed no significant problems in past FAA inspections, he said.
Nigel Turner, chief executive of Las Vegas-based Heli-USA, said the aircraft, one of six in his Hawaii fleet, was minutes from its scheduled landing when it crashed.
"We are in the process of notifying the families of those individuals involved and our sincere condolences goes out at this time," he said. "We are working with authorities to find out exactly what happened."
Turner defended the safety of his helicopters, which also fly tours in Nevada.
"The company has flown over a million passengers. This is our second accident in a million people," he said. He said he wouldn't hesitate to put his own family in his helicopters.
The crash comes one month after the FAA announced new safety standards for air tour companies that operate at many scenic vacation spots around the country and for pilots who offer rides at air shows.
The FAA promised to closely monitor deaths and other accidents involving air tours after looking into 107 accidents that killed 98 people between 1988 and 1995. The safety rule takes effect in August.
The safety board on Feb. 13 also called for tougher standards for monitoring of tour operators across the country based on two earlier crashes on Kauai, including one involving a Heli-USA helicopter.
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"When you have a hydraulic failure, you're perfectly able to get to the ground," Danko said. "If you have the floats out, you're no longer able to skid."
In the last 10 years, there have been 20 helicopter sightseeing tour accidents in Hawaii, 10 in Arizona, eight in Alaska and one in New York.