JUNEAU, Alaska (AP) — The probable cause of a heli-skiing crash in Alaska in 2021 that killed a Czech billionaire and four others was a failure by the pilot to adequately respond to whiteout conditions, a federal accident report released Wednesday concluded.

The report from the National Transportation Safety Board found that an “inadequate pilot training program” by the helicopter operator and “insufficient oversight” by a Federal Aviation Administration inspector were contributing factors.

One person survived the crash, and a delay in notifying search and rescue teams contributed to the severity of his injuries, which included “extensive frostbite damage to both hands,” the report said.

The family of Petr Kellner, who at the time of the crash was the richest man in the Czech Republic, filed a lawsuit this year against the helicopter operator, Soloy Helicopters, and others, in state court.

Soloy representatives said the aircraft was under contract to Tordrillo Mountain Lodge to carry the group from a private home in Wasilla, north of Anchorage, to the Chugach Mountains for a heli-skiing trip, according to the report. Triumvirate LLC, which owns and operates Tordrillo Mountain Lodge, is also a defendant in the lawsuit.

Soloy Helicopters referred a request for comment on the NTSB report to a spokesperson, who did not immediately respond Wednesday. A message seeking comment also was sent to the FAA.

Those killed in the crash were Kellner, 56, and Benjamin Larochaix, 50, of the Czech Republic; guides Gregory Harms, 52, of Colorado, and Sean McManamy, 38, of Girdwood, Alaska; and pilot Zachary Russell, 33, from Anchorage. David Horvath, of the Czech Republic, survived. He also has filed a lawsuit related to the ordeal.

Horvath told investigators that before what was to be the last ski run of the day, Russell attempted to land on a ridgeline but the helicopter lifted off for an attempted second landing. During the second attempt, Horvath said, the snow was light but the helicopter became “engulfed in a fog which made it appear like a little white room,” and subsequently, the aircraft hit the ridgeline and rolled downhill, according to the report.

Horvath also recalled another passenger yelling “don’t do it” three times just before the crash.

“The passenger’s recollection of the conditions just before the accident was consistent with whiteout conditions caused by rotor wash while the helicopter was hovering near the ridgeline,” the report said. “Thus, the pilot likely experienced whiteout conditions during the second landing attempt, which caused him to lose visual reference with the ridgeline and resulted in the helicopter impacting terrain.”

The NTSB report said Soloy had an “inadequate pilot training program and pilot competency checks,” which it determined to be a contributing factor, along with “insufficient oversight of the operator” by an FAA inspector that included “approval of the operator’s pilot training program without ensuring that it met requirements.”

The inspector had prior ties to Soloy, including as a former pilot, the report said. But the NTSB said there was insufficient evidence to determine whether the inspector’s prior work history was a factor “in the adequate oversight.”

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Thiessen reported from Anchorage.