The pilot of the plane that crashed and left nine dead in South Dakota took off with limited visibility in snowy and turbulent weather, according to the National Transportation Safety Board.
The pilot initially filed with the Federal Aviation Administration a plan with instrument flight rules (IFR), which describe how an aircraft operates when a pilot is unable to navigate with visual references.
Visibility around the time of takeoff was about half a mile, with moderate snow and icing, along with overcast skies and turbulent conditions, the NTSB said Monday.
The single-engine Pilatus PC-12 was then cleared Saturday to fly from Chamberlain Municipal Airport to Idaho Falls, Idaho, the NTSB said.
Though clearance gives pilots permission to use the runway, it does not suggest that they are necessarily OK to go in the weather conditions they face. The decision to fly or not, in small-aircraft operations, rests on the pilot, CNN transportation analyst Mary Schiavo said.
When the pilot didn't activate his flight plan after departure, the FAA issued an alert for a missing plane, the NTSB said. The plane crashed one mile north of the Chamberlain airport.
Twelve people were on the flight and three survived, the NTSB said. The survivors were taken to Sioux Falls for treatment.
Four generations of an Idaho Falls family were killed in the crash while traveling on a hunting trip. Brothers Jim and Kirk Hansen, founders of health and wellness company Kyäni Inc., were on the plane with their father, Jim Hansen Sr., Kyäni president Travis Garza said in a statement.
Also killed were Jim Hansen Jr.'s son, Jake Hansen, and Jake's son, Houston. Kirk Hansen's sons, Stockton and Logan, and his sons-in-law, Kyle Naylor and Tyson Dennert, died in the crash.
Three NTSB investigators arrived at the crash site Monday after being delayed by inclement weather, the agency said. They're expected to complete their work in Chamberlain by the weekend. A preliminary report on the crash is expected to be published in two weeks, the NTSB said.
The entire investigation to determine the cause of the crash is expected to be completed within one to two years, the agency said.
Correction: A previous version of this story incorrectly characterized the pilot's clearance. The decision on whether to fly rests on the pilot.
CNN's Eliott C. McLaughlin, Dave Alsup and Shawn Nottingham contributed to this report.