The pilot in a sightseeing flight’s fatal 2014 crash near Atigun Pass is accused of obstructing federal officials’ work to investigate it, prosecutors announced Thursday.

Forest Kirst, 60, is charged with two counts of obstruction before the National Transportation Safety Board regarding the Aug. 24, 2014 crash, as well as piloting an aircraft without a valid airman’s certificate, U.S. Attorney for Alaska Bryan Schroder’s office said in a statement.

“Kirst is charged with misleading the NTSB about the altitude of his plane prior to the crash and misleading the NTSB with varying explanations as to how the crash occurred,” federal officials wrote.

NTSB officials said at the time that the four-seat Kirst Aviation aircraft took off from Fairbanks and was bound for Bettles, Deadhorse and Barter Island before heading back to Fairbanks.

A Kirst Aviation Ryan Navion A at the site of an Aug. 24 , 2014 plane crash which killed one of four people on board. (From FAA via NTSB)

The Ryan Navion A went down roughly 56 miles north-northeast of Coldfoot, leaving Kirst and three Canadian passengers – 66-year-old Darrell Spencer, 57-year-old Daphne McCann and 65-year-old Marcene Nason – with serious injuries. NTSB staff said at the time that Alyeska Pipeline workers at a pump station reported the crash to Alaska State Troopers; all four of the plane’s occupants were flown to hospitals for treatment, but Spencer died a month after the crash of his injuries.

A final NTSB report issued this March attributed the crash to Kirst’s “improper decision to deliberately operate the airplane at low altitude in close proximity to obstructions and rising terrain,” as well as his decision to take off with the aircraft loaded beyond its maximum gross weight. The report also cited the Federal Aviation Administration’s decision to issue Kirst a flight certificate, despite a “history of accidents, incidents, reexaminations, and checkride failures,” as a contributing factor.

According to the report, Kirst had claimed in a statement following the crash that his plane had lost a propeller blade in flight. Neither accounts of the crash from passengers nor evidence at the scene corroborated that claim, however, and a metallurgical test showed that the blade failed due to overload with no evidence of fatigue cracking found.

Schroder's office said the FAA revoked Kirst's flight certificate on an emergency basis following the crash investigation, but he "was later observed to be flying his aircraft."

Clint Johnson, the NTSB’s Alaska chief, said the agency was unable to comment on the crash because it is now a criminal matter.

“Our investigation is done and the case is now in the hands of the U.S. Attorney,” Johnson said.

Chloe Martin, a spokeswoman for Schroder’s office, didn’t immediately have detail Thursday on when criminal concerns first emerged about Kirst’s statements.

“The grand jury just returned the indictment this morning,” Martin said.

If Kirst is convicted in the case, which was investigated by the U.S. Department of Transportation’s Office of Inspector General, he faces a maximum penalty of five years in prison, a $250,000 fine or both.

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