The pilots of an Army Black Hawk helicopter that crashed into the ocean off Kaena Point on an Aug. 15, 2017, night training flight, killing all five aboard, experienced “spatial disorientation” and hit the water with “tremendous force” nose down and banked to the right, according to an Army investigation.

Two Black Hawks from Wheeler Army Airfield were flying in tandem at about 1,000 feet and 126 mph when the aircraft that crashed, “Army 20556,” entered a right turn about six rotor spans away from the other helicopter.

The aircraft that crashed continued in a right bank as the nose began to slowly pitch down and the helicopter began to climb slightly, the investigation reported.

About nine seconds into the turn, the right bank and downward nose pitch increased until the UH-60M rolled into a descending left bank.

At 9:13 p.m. the helicopter “abruptly rolled back to the right while it continued to descend with a nose-down attitude,” impacting the water about a mile west of Kaena Point, the report said. The aircraft broke into multiple pieces and came to rest at 130 feet down on the ocean floor.

Spatial disorientation occurs when a pilot can’t determine his or her position and attitude relative to the earth’s surface.

“Despite decades of awareness to this killer within the aviation community, (spatial disorientation)-related accident rates have not declined substantially over the years, contributing to approximately one-third of all mishaps,” the U.S. Army Aeromedical Research Laboratory said in a 2012 report.

The Oahu crash occurred after the two choppers left Wheeler for night-vision goggle training over water in zero-illumination conditions.

Officials in late August 2017 declared as deceased Chief Warrant Officer Brian M. Woeber, 41, and Chief Warrant Officer Stephen T. Cantrell, 32. The Armed Forces Medical Examiner previously had made the determination for 1st Lt. Kathryn M. Bailey, 26; Staff Sgt. Abigail R. Milam, 33; and Sgt. Michael L. Nelson, 30, after trace remains discovered among floating debris were matched to their DNA.

All the crew members, who were with the 2nd Battalion, 25th Aviation regiment, died of multiple blunt force trauma, the report said.

Woeber, who had 2,264 total flight hours and had served two combat tours, was in the left seat as pilot in command and acting as a “standardization instructor pilot” on the night of the crash, according to the investigation, which was obtained by the Honolulu Star-Advertiser through a federal Freedom of Information Act request.

Bailey, who had 202 total flight hours, was receiving night-vision goggle and multi-aircraft formation training, and was on the flight controls in the right seat at the onset of the accident sequence, the report said.

The investigation was conducted by the U.S. Army Combat Readiness Center at Fort Rucker, Ala., and is intended mainly for accident prevention purposes. As such, many parts of the report are exempt from release, the Army said.

The review found no apparent administrative errors and no materiel or mechanical defects.

The overall findings and recommendations are redacted from the report. A second investigation, an Army 15-6 inquiry, is expected to be made public.

At 8:59 p.m. the two Black Hawks departed Wheeler in a staggered formation, climbed to 2,500 feet, crossed Maili Point at the coastline and descended to 1,000 feet.

Milam, a crew chief, was being evaluated for her annual proficiency and readiness test by Nelson, a standardization instructor. Cantrell, a Black Hawk maintenance test pilot, was performing duties as a crew member.

The overall risk for the flight was assessed as “low” by the crew and mission briefing officer.

The crash was not seen by anyone aboard the first helicopter because one crew member, who had been observing the aircraft, became preoccupied with a fuel consumption check, the report said.

After receiving no reply on their radio, the investigation said, the remaining helicopter turned back and searched for the missing aircraft for 10 minutes and then returned to Wheeler to see whether the other chopper had possibly lost communication and returned to base.

Other Army helicopters, along with Marine Corps and Coast Guard aircraft, subsequently searched for the missing helicopter and spotted a debris field.

Initial search and rescue efforts on Aug. 16 and 17, 2017, resulted in the recovery of suspected human remains, most of which were small pieces, the report said.