The preliminary investigation report by the National Transportation Safety Board said the available information, as well as the type of damage to the aircraft, leads investigators to suspect a loss of engine power in the July 23 crash into Wai‘ale‘ale Crater.

A look at the engine found no evidence of damage from a foreign object, the fuel filter was full, the fuel lines were not blocked and the fuel was not contaminated, according to the preliminary investigation.

The Rolls Royce engine was flown to the Mainland for a teardown and inspection.

The helicopter, a Bell 206B Jet Ranger owned by Jack Harter Helicopters, crashed on steep terrain inside the northwestern crater wall about 4,700 feet up the slope. The wreckage slid about 300 feet farther down.

The impact immediately killed four of the five people aboard, but rescue firefighters airlifted in found one passenger, Monica Peterson, 33, of Denver, alive. Heavy clouds prevented the firefighters from evacuating Peterson before she died.

The preliminary investigation noted that “the crater area was unusually clear” prior to the crash.

The pilot for the one-hour tour, Mark Lundgren, 44, flew counter-clockwise around Kaua‘i and reported to another pilot in the area that he was at the crater and flying a “741 to the top.” The jargon is used by the tour company to communicate about a flight to the top of the crater rim, the report said.

A clock on the helicopter’s instrument panel had stopped at 8:52, about 28 seconds after Navy radar data noted the helicopter about 4,900 feet up the crater wall.