Four people were fatally injured and three critically injured Thursday in a tour helicopter crash on Kauai, officials said.

The crash occurred at Princeville Airport at about 3 p.m., shortly after a Heli-USA Airways helicopter pilot radioed that he was having problems with the aircraft's hydraulics, according to a statement by Kauai Fire Chief Robert Westerman.

Of the two men and two women who died, three were killed in the crash and one died while being taken to Wilcox Memorial Hospital, where the three survivors were being treated, Maui County spokeswoman Mary Daubert 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."

He said the pilot is "very experienced," but would not confirm if he was among the survivors. 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, adding that he would not hesitate to put his own family in his helicopters.

The National Transportation Safety Board and the Federal Aviation Administration were unable to immediately provide additional details.

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, does not take effect until 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.

The safety board said the two previous Kauai helicopter crashes were caused by bad decisions by pilots who continued flying in dangerous weather conditions.

"The air tour industry in Hawaii serves hundreds of thousands of paying passengers each year and the public deserves an appropriate level of safety when they embark on an air tour," board chairman Mark V. Rosenker said in a statement.

Five people, including the pilot, were killed Sept. 24, 2004, when a helicopter operated by Bali Hai Helicopter Tours Inc. crashed into a mountain on Kauai. And three passengers drowned Sept. 23, 2005, after a Heli-USA helicopter plunged into the Pacific Ocean near Kauai's Na Pali Coast.