LOS ANGELES — The National Transportation Safety Board will hold a hearing on Feb. 9 to determine the cause of the helicopter crash a year ago that killed Los Angeles Lakers legend Kobe Bryant, his daughter Gianna and seven others when it struck a fog-covered hillside in Calabasas.

The NTSB, in a preliminary report, ruled out engine and mechanical failure on the Sikorsky S-76B helicopter. But it has yet to provide a probable cause for the Jan. 26, 2020, crash.

More than 1,700 pages of investigative documents that examine all aspects of the crash of the chopper, however, strengthened a widely held view among helicopter experts that pilot Ara Zobayan may have become disoriented while he navigated through foggy conditions on the Sunday morning flight from Orange County to Camarillo.

Zobayan told air traffic control they were “climbing” to 4,000 feet, when in reality the aircraft was descending. The NTSB’s aircraft performance study said the helicopter banked left and away from the 101 Freeway while communicating with the controller. According to the study, the pilot “could have misperceived both pitch and roll angles,” according to the NTSB documents.

“When a pilot misperceives altitude and acceleration it is known as the ‘somatogravic illusion’ and can cause spatial disorientation,” the report said. In other words, acceleration could cause a pilot to sense his aircraft was climbing when it was not.

The helicopter crashed into the hillside near Las Virgenes Road and Willow Glen Street at 9:45 a.m. Pacific time.

A witness on a mountain bike trail told investigators that the area was “surrounded by mist” and that he heard the sound of a helicopter and saw a blue and white chopper emerge from the clouds, passing from left to right. The NTSB reports noted that videos and photos from the public “depict fog and low clouds obscuring the hilltops.” The reports noted that the pilot had struggled with a “low cloud ceiling.”

The NTSB’s operational factors and human performance report said, “Evidence of the accident pilot receiving a weather briefing from an approved source could not be determined.”

The night before the crash, the broker arranging the flight had expressed concerns to the pilot that “weather could be an issue.” Zobayan assured the broker the next morning that it “should be ok,” according to text messages released by the NTSB.

The 1991 Sikorsky S-76B was carrying parents, coaches and players to a youth basketball game at Bryant’s Mamba Academy in Thousand Oaks. Besides Bryant and his daughter, those who perished in the crash were Christina Mauser; Payton and Sarah Chester; John, Keri and Alyssa Altobelli; and Zobayan. John Altobelli was the longtime baseball coach at Orange Coast College.

At the conclusion of the Feb. 9 virtual hearing to determine the probable cause of the crash, the NTSB will likely make recommendations to improve aviation safety going forward for such helicopters.

Jennifer Homendy, an NTSB board member who led the on-scene investigation, has already said the helicopter did not have a terrain awareness system, TAWS, that may have helped inform the pilot of his nearness to the ground and was not required on that particular chopper under Federal Aviation Administration regulations. The NTSB has previously recommended such a system on all large passenger helicopters.

The hearing is scheduled at 9:30 a.m. EST in Washington, D.C., and will be webcast. A link to the webcast will be available shortly before the start of the meeting at http://ntsb. windrosemedia.com/.