The crash killed all seven people onboard.
The NTSB report, released Wednesday, did not indicate a possible cause but said a witness reported “adverse weather conditions" around the time of the crash.
The pilot didn’t make a “mayday” report or indicate any type of emergency before the crash.
Safari Helicopters, which ran the tour, start “flight-locating procedures” at 5:31 p.m. on Dec. 26 — 10 minutes after the helicopter was due to return to Lihue.
The chopper was found the following morning in remote, mountainous terrain inside Kokee State Park.
The NTSB said the helicopter’s pilot was last heard from at 4:45 p.m. as he reported that the helicopter was exiting Waimea Canyon and heading into Kokee State Park.
At about 4:57 p.m., the NTSB has said, the helicopter hit a north-facing slope at an elevation of about 3,000 feet, burst into flames and came to rest about 100 feet below where the aircraft made impact.
In the NTSB report, investigators said a witness who was about 1 1/2 miles from the crash site heard “what he described as a hovering helicopter followed by a high-pitched whine.”
At the time, the witness said, the weather had turned bad and visibility was at just 20 feet.
“Knowing something was wrong, he attempted to locate the helicopter but was unable due to the adverse weather conditions and fading daylight,” the NTSB said.
While the wreckage was consumed by fire, investigators said, all the chopper’s main components were located within the debris field.
In addition to the 69-year-old pilot, a mother and daughter from Wisconsin and a family of four from Switzerland were killed in the crash.
Investigators have said they’ll be looking at a number of factors as they try to determine the cause of the crash, including weather conditions and the potential of mechanical issues or pilot error.
A final report could take years to complete.