An NTSB investigator examines the wreckage of a Pilatus PC-12 airplane at Chamberlain Municipal Airport in South Dakota. The aircraft crashed on Saturday, November 30, 2019, moments after taking off. The crash killed nine of the 12 people on board. (NTSB) The pilot and a passenger worked for three hours “to remove snow and ice from the airplane,” according to a National Transportation Safety Board (NTSB) preliminary report, prior to a deadly plane crash late last month in South Dakota that claimed the lives of nine passengers and injured three others.The NTSB said a witness recalled having seen the efforts to clear the single-engine Pilatus PC-12 before the plane took off and then crashed within a mile of takeoff in Chamberlain, South Dakota, Nov. 30.”If you have the proper equipment it shouldn’t take three hours, especially for a plane that size,” Ethan Klapper, a journalist and licensed aircraft dispatcher, told AccuWeather. “Sounds like something improper happened here. Also, they were clearing the snow while it was still snowing. So likely there was additional accumulation that was occurring during this, and they took off with still more snow that accumulated on the aircraft.”Chamberlain, and much of South Dakota, was under a Winter Storm Warning from the National Weather Service at the time of the crash. Winds of 7 mph and moderate snow were reported at the time of the flight with overcast conditions and half-mile visibility, according to the report. Freezing rain and snow were observed at the Chamberlain Municipal Airport the previous afternoon and overnight.The plane arrived in Chamberlain Friday at about 9:30 a.m. CST, according to an earlier NTSB statement. The airplane remained parked on the airport ramp until the accident a day later.”It seems a classic case of no deicing chemicals were sprayed or that there was some kind of buildup of new snow on the wings,” said AccuWeather Senior Meteorologist Alex Sosnowski. “Or is it possible the air speed indicator was clogged with, or again became clogged with, snow and ice? Or, did they damage something on the plane while clearing it of snow and ice?” A photo of a Pilatus PC-12 in flight. (Pilatus Aircraft Ltd) Ice and snow need to be properly removed from a plane for the flight to be legal, and if that doesn’t happen, the consequences can be dire. Variations in drag and lift could be substantial if a plane is not properly deiced, an aviation expert confirmed with AccuWeather.Three of the plane’s warning systems – the stall warning, stick shaker and stick pusher – activated within 15 seconds after liftoff, the NTSB report noted. The airplane immediately rolled about 10 degrees to the left after takeoff. The plane then reversed to five degrees to the right before it “ultimately entered a 64-degree left bank as the airplane reached its peak altitude of 460 feet above ground,” according to the report.It’s also possible the time taken to clear the plane’s snow and ice affected pre-flight preparations. The pilot and passenger worked for three hours before being joined by the remaining passengers shortly before the flight, according to the NTSB report. The pilot requested clearance from Minneapolis Air Route Traffic Control Center (ARTCC) at 12:24 p.m., saying he’d be ready in five minutes. At 12:27 p.m., he received clearance with a void time of 12:35 p.m. No radio communications were received from the pilot and radar contact was never established. At 12:40 p.m., Minneapolis ARTCC contacted the Chamberlain airport manager, who advised the plane had departed about 10 minutes earlier. An alert notice was then issued.Another factor that could have contributed to the crash was a possible load imbalance. The Pilatus PC-12 pilot’s information manual notes the “maximum number of occupants is 9 passengers” plus 1-2 pilot(s). According to the NTSB report, there were 12 people on the plane.The data recorder captured cockpit sound, the report noted; the NTSB will convene a group of technical experts to produce a transcript. The preliminary report does not include analysis or a probable cause for the accident. Probable cause will be determined at the end of the investigation, which could take between 12-14 months to complete.According to Travis Garza, president of wellness company Kyani, the company’s two founders, Jim Hansen and Kirk Hansen, were among the crash victims. The other seven passengers who died were their relatives; three passengers survived.There were 393 U.S. civil aviation deaths in 2018, an increase from 347 in 2017, according to the NTSB. Most aviation deaths in 2018 took place during general aviation operations – all civilian flying except scheduled passenger airline service – when 381 were killed, compared to 331 in 2017.