JUNEAU, Alaska — The surviving passenger of a deadly Alaska helicopter crash told federal investigators that the aircraft entered a freefall from about 500 feet (152 meters) in the air before smashing onto a beach in Glacier Bay National Park last month.

The National Transportation Safety Board released a preliminary report last week on the Sept. 28 crash the killed both pilots and an 11-year-old boy, the Juneau Empire reported Sunday.

The 14-year-old survivor told an NTSB investigator that the pilot “reached down and rolled the throttle off” before the helicopter entered the free fall.

The pilot increased throttle, but the helicopter hit shallow water near Lituya Bay, about 60 miles (97 kilometers) northwest of Gustavus. The passenger went unconscious after the impact, according to the report.

The passenger did not understand the pilot's actions, and "at this point, neither do we," investigator Joshua Lindberg said.

The helicopter had taken off from the Juneau airport and was traveling to Yakutat. The aircraft was being delivered to Anchorage from the Airbus Helicopters factory in Grand Prairie, Texas, according to the report.

The crash killed 53-year-old David King of Palmer, 42-year-old Joshua Pepperd and Andrew Pepperd, both of Anchorage. Aiden Pepperd was injured, but was rescued by the U.S. Coast Guard.

Investigators visited the wreckage site two days after the wreck. The helicopter's tailboom, tail rotor assembly and most of the instrument panel were not found. The NTSB recovered the engine data recorder, engine control unit and a camera that monitored the instruments and the pilot's actions.

Lindberg said determining the cause of the crash will take time, possibly more than a year.

“The reason that those take so long is that there’s a lot of information to process,” Lindberg said. “There’s a lot that goes into an accident like this.”