NA PALI COAST — The National Transportation Safety Board released a preliminary report on the March 26 crash of an Airborne Aviation sightseeing helicopter off Kalalau Beach on Kauai's North Shore, finding that the aircraft experienced intense vibrations and a spin before striking the water. The report did not identify a suspected cause of the accident.

The helicopter was carrying the pilot and four passengers when it crashed. Margaret Rimmler, 65, and Patrick Haskell, 59, both from Massachusetts, and Oksana Pihol, 40, a Ukrainian national, were killed. The pilot and a surviving passenger sustained serious injuries.

According to the preliminary report, the vibrations began as the pilot made a left turn away from the shoreline as part of the normal flight pattern. The helicopter then began quickly rotating clockwise. The pilot put the aircraft in an autorotation, a maneuver that allows the rotor to spin with the force of air rather than by engine power, to stop the spin. The pilot told investigators, "A high frequency vibration throughout the helicopter came in waves and became stronger each time."

The pilot made a mayday call before crashing into the water about 75 yards (69 meters) off the beach. The helicopter rolled onto its right side and became partially submerged. A witness flying near the accident site saw the helicopter appeared intact before it struck the water and broke apart.

Aviation safety expert Jeff Guzzetti said the vibrations and sudden spin suggest a mechanical problem likely in the tail rotor. "Certainly it seems to lead to a mechanical failure in the helicopter, which would point the investigation to maintenance and design issues," Guzzetti said. He said the pilot did the right things by stopping the spin but did not have enough time or altitude to reach the beach.

Airborne Aviation offers sightseeing tours of Kauai's canyons, shoreline and waterfalls, including a "doors-off thrill seekers adventure tour" that seats up to four people. The area's tall seaside cliffs and sharp mountain ridges can contribute to turbulent air and quick weather changes that pose hazards for aviation.

At least 16 people have died in helicopter crashes in Hawaii in the past seven years, including two crashes in 2019. Sightseeing companies in other parts of the country, including New York, have also had crashes. Five people died in a 2018 crash when a charter helicopter offering "open door" flights went down into the East River. A 2009 collision between a plane and a tourist helicopter over the Hudson River killed nine people.