The pilot of the helicopter which crashed killing basketball superstar Kobe Bryant, his young daughter, and seven other people had probably become disorientated amid fog, US safety investigators have said.
The helicopter smashed into a hillside near Calabasas, California, on 26 January 2020.
Pilot Ara Zobayan was among the dead.
He had told air traffic controllers the helicopter was climbing out of heavy cloud when it was actually descending.
"This manoeuvre is consistent with the pilot experiencing spatial disorientation in limited visibility conditions," Robert Sumwalt, chairman of the US National Transportation Safety Board (NTSB), said on Tuesday.
The NTSB has been investigating the circumstances around the crash, and is meeting shortly to vote on the probable cause. It is an independent federal agency with no enforcement powers.
Zobayan violated federal rules and went against his own flight training by flying into thick clouds, safety officials said.
The pilot "was flying under visual flight orders or VFR which legally prohibited him from penetrating the clouds", but he did so anyway, said Mr Sumwalt.
Investigators also criticised Zobayan for banking the helicopter to the left, instead of bringing the aircraft straight up while trying to escape the bad weather.
Zobayan was an experienced pilot who had often flown for Bryant. The widely respected pilot had logged more than 1,200 hours in the Sikorsky-76 helicopter.
Disorientation can set in when pilots can't see the sky or landscape, making it harder to judge an aircraft's altitude and acceleration.
Mr Sumwalt said the board would also discuss "whether the pilot faced pressure to complete the flight".
"What were the expectations of the pilot under the company policy?" he asked. "Did he put pressure on himself, and what actions could he have taken to avoid flying into the clouds?"
Investigators have said that the close relationship between Bryant and Zobayan may have compelled the pilot to fly even in unsafe conditions.
In text messages on the eve of the crash released by the NTSB, Zobayan wrote that the forecast seemed to be "not the best". The next morning, he wrote that the conditions were "looking ok".
The NTSB previously said there was no evidence of mechanical failure in the Sikorsky S-76B helicopter.
The helicopter was not required to have "black box" recorders, which capture flight data and voices in the cockpit, and was not carrying any.
At the time of the crash, retired NBA legend Bryant, 41, was travelling to a youth basketball tournament with his 13-year-old daughter, Gianna, two of her teammates, and several other friends.
The fatal crash prompted a global outpouring of support for the NBA star and his family - as well as a number of lawsuits.
Bryant's wife, Vanessa Bryant, sued Zobayan and the companies that owned and operated the helicopter for alleged negligence and wrongful death. Families of the other victims sued the helicopter companies - but not Zobayan.
In September, Ms Bryant sued the Los Angeles County Sheriff's Department after officers shared unauthorised photos of the crash site. California now has a state law prohibiting first responders from taking unauthorised pictures of people who died at the scene of an accident or crime.