LOS ANGELES (Reuters) – The pilot of a helicopter that crashed outside Los Angeles in January, killing basketball great Kobe Bryant, his daughter and all seven others on board, likely became disoriented in the fog, federal investigators said on Wednesday.

Pilot Ara Zobayan told air traffic controllers that his chopper was climbing out of heavy clouds when in fact it was descending immediately before slamming into a hillside near the town of Calabasas, the National Transportation Safety Board wrote in newly released findings.

The board, which has not yet issued a final report on the cause of the Jan. 26 accident, said pilots can become confused about an aircraft’s attitude and acceleration when they cannot see the sky or landscape around them, causing “spatial disorientation.”

“Without outside references or attention to the helicopter’s attitude display, the actual pitch and bank angles have the potential to be misperceived,” the NTSB said. Zobayan was killed in the wreck.

An NTSB board member told reporters in the days after the crash that clouds and fog causing limited visibility in the foothills north of Los Angeles would likely be a key focus of the investigation.

In February the board said an examination of the helicopter’s engines and rotors found no evidence of “catastrophic mechanical failure” that could explain why the airship would have suddenly plunged into the terrain. [L1N2A71FY]

A series of charts issued with the NTSB report shows the aircraft gaining speed, banking sharply to the left and plummeting just seconds after Zobayan told air traffic controllers he was “climbing to 4,000” feet to fly above the cloud layer.

Bryant, an 18-time National Basketball Association all-star, was traveling with his 13-year-old daughter, two other girls and others to a youth basketball tournament at the time of the crash, which prompted an outpouring of shock and grief from sports fans worldwide.