The civilian pilot of the tour helicopter that crashed off the USS Arizona Memorial visitor center last week told a crash investigator that he felt “a vibration” followed by a grinding noise, then “a loud bang” before he was forced to crash-land, fatally injuring one of four passengers on board, according to a preliminary report by the National Transportation Safety Board.

Killed from injuries he sufferred in the crash of the Bell 206B Jetranger helicopter was Riley Dobson, 16, of Ontario, Canada, according to the Medical Examiner’s office.

An autopsy will be conducted to determine cause of death.

Two family members, a 50-year-old man and 45-year-old woman, remain in stable condition at Pali Momi Medical Center, the hospital said. Another family member was treated at an area hospital and released Thursday.

Rescuers said they had to cut the seat belt strapping the boy into his seat before they could free him from the submerged helicopter.

Pilot Ryan Rohner was flying the aircraft owned by tour company Genesis Helicopters when it crashed with four passengers aboard at about 10:30 a.m. on Thursday, 20 feet from the USS Arizona Memorial visitors center.

Rohner, who has been a pilot with the Hawaii Army National Guard since 1999, told an NTSB investigator that while in cruise flight over Ford Island, he felt a vibration followed by a grinding noise.

“Shortly after, the pilot heard a loud bang, scanned the instrument panel and saw that the engine instruments indicated the engine was still running, however, rotor rpm decreasing,” the report said.

“The pilot initiated an auto rotation to a grassy area near Contemplation Circle at the World War II Valor in the Pacific National Monument. As the pilot neared his intended landing area, he observed multiple people within the area. The pilot stated he initiated a left pedal turn, attempting to land close to the shoreline. Subsequently, the helicopter descended rapidly into the water, about 20 feet from the shoreline.”

Talking with an air traffic controller seconds before the crash, Rohner said he was heading toward the south ramp at Ford Island. An air traffic controller then asks the pilot to head instead toward the federal prison and hold in place for further direction.

Rohner acknowledges the request.

Twenty-two seconds later, Rohner issued a distress call: “Tower. Chopper 8. I think I’m going down.”

Rohner, a UH-60 Black Hawk helicopter pilot and a chief warrant officer, remains hospitalized at Tripler Army Medical Center. He is a pilot with Detachment C, 1st Battalion, 207th Aviation Regiment, according to the Hawaii Army National Guard.

Dobson was a horse jumper who competed in several equestrian shows throughout Ontario. He was a high school student at Centennial Collegiate Vocational Institute in Guelph, according to the Waterloo Region Record, an Ontario newspaper. In honor of the teen, flags flew at half-mast outside his high school, Centennial Collegiate Vocational Institute, this week.

The NTSB report said witnesses located at various locations at the World War II Valor in the Pacific National Monument reported observing the helicopter near their location traveling at a low altitude before it suddenly descended into the water.

The helicopter was submerged in about 40 feet of water.

The helicopter was recovered the day after the accident and rinsed with fresh water. All major structural components of the helicopter were recovered.

The wreckage was moved to a hangar at Honolulu Airport operated by Genesis Helicopters for further examination.