By Kanishka Singh

WASHINGTON The March 2021 helicopter crash in Alaska that killed billionaire Petr Kellner and four others was likely caused by pilot error and inadequate training, a report by the U.S. National Transportation Safety Board (NTSB) said on Wednesday.

Kellner, who was at the time the Czech Republic's richest man and founder of investment group PPF, was killed in the crash on a heli-skiing trip in Alaska. The crash took place near Knik Glacier northeast of Anchorage.

The NTSB determined that the probable cause of the accident was "the pilot's failure to adequately respond to an encounter with whiteout conditions, which resulted in the helicopter's collision with terrain."

The operator's inadequate pilot training program and pilot competency checks also contributed to the accident, the NTSB report added.

It also said the Federal Aviation Administration (FAA) principal operations inspector's "insufficient oversight of the operator" contributed to the incident. One passenger had survived the crash but there was a delayed notification of search and rescue organizations, the NTSB report showed.

Kellner was a towering figure in the Czech Republic's post-communist era, amassing wealth estimated at the time of his death at $17.5 billion according to Forbes.

He was the world's 68th richest person on Forbes' 2020 list, tied with media giant Rupert Murdoch and his family.

His heirs filed a lawsuit in Alaska in April in the quest for a probe into "potential negligence" that caused the deadly crash.

(Reporting by Kanishka Singh in Washington; Editing by Lincoln Feast.)