No clear answers for cause of 2018 Alaska sightseeing crash in Denali
Investigation hindered by inaccessibility of aircraft after it was buried by calving glacier
Federal investigators couldn't determine why a sightseeing plane crashed in Denali National Park and Preserve last year, killing all five people on board, because they couldn't access the crash site.
The plane went down on a steep, hanging glacier at over 3,048 metres in elevation. The glacier calved last winter, burying the plane in up to 5,443 metric tonnes of ice, Anchorage TV station KTUU reported.
The National Transportation Safety Board, in its final report on the August 2018 crash, lists the probable cause as "impact with terrain for reasons that could not be determined because the airplane was not recovered due to the inaccessible nature of the accident site."
Typically, toxicology reports are conducted on pilots and mechanical assessments are done on the wreckage, but that wasn't possible in this case.
Forty-eight minutes into the plane's flight, the Alaska Rescue Coordination Center received an alert from its emergency locator. Moments later, personnel from the plane's operator, K2 Aviation, received a call from the pilot reporting the plane had "run into the side of a mountain."
Poor weather conditions hampered initial efforts to locate the plane. An eventual assessment of the scene indicated a wing had hit the snow while the airplane was flying in what was likely reduced visibility, the report states.
The National Transportation Safety Board said the aviation company did not use a formal risk assessment process, instead relying on conversations between pilots and the flight follower in Talkeetna or Anchorage.
"This could lead to an oversight of actual risk associated with a particular flight route and weather conditions," the report states.
K2 Aviation's base chief pilot said routes for glacier tour flights were subject to change at the pilot's discretion based on the weather at the time of the flight to provide the best tour experience, according to the report.
That individual also stated that pilots were expected to report to base operations when changing a planned route, but this was not a requirement in the company's general operations manual, the report states.
The company's operators were out of country Wednesday and unavailable for comment, KTUU reported.