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At a Glance Fog could have caused the pilot to become disoriented.

The charter company that owned the helicopter was not authorized to operate under such conditions.

Investigators have asked people to send them photos of weather conditions in the area at the time. As more details emerge about the helicopter crash that killed NBA star Kobe Bryant, his daughter and seven other people, experts say it's likely that weather played a key role.

Specifically, fog and low visibility may have caused pilot Ara Zobayan to become disoriented. What's more, the charter company Zobayan was flying for was not licensed to operate in such conditions and lacked a warning system to alert pilots when an aircraft gets too close to the ground, according to several media reports.

“The largest killer in aviation, bar none, is weather ,” Michael Lenz, a retired safety program analyst with the Federal Aviation Administration, told the Los Angeles Times. “The types of weather where this occurs aren’t usually severe like thunderstorms, but simply restrictions to visibility.”

(MORE: Kobe Bryant's Helicopter Was Given Special Clearance to Fly in Sunday's Foggy Weather)

<img class="styles__noscript__2rw2y" src="https://s.w-x.co/util/image/w/GettyImages-1197352766.jpg?v=at&w=485&h=273" srcset="https://s.w-x.co/util/image/w/GettyImages-1197352766.jpg?v=at&w=485&h=273 400w, https://s.w-x.co/util/image/w/GettyImages-1197352766.jpg?v=ap&w=980&h=551 800w" > In this handout photo provided by the National Transportation Safety Board, an investigator works at the scene of the helicopter crash that killed former NBA star Kobe Bryant and his 13-year-old daughter Gianna on Jan. 27, 2020 in Calabasas, California. All nine people on board, including the pilot, perished in the crash as they were flying to Bryant's Mamba Sports Academy in Thousand Oaks, where he was going to coach Gianna in a tournament game. (James Anderson/National Transportation Safety Board via Getty Images)

Zobayan was certified to fly under instrument flight rules, which allow pilots to be guided by their instruments when visibility is low. But Island Express Helicopters, the charter company that owned the aircraft, was not , NBC News reported Friday.

“Speaking generally, a pilot has to observe any limitations on the company he or she works for, regardless of the pilot’s personal ratings,” the Federal Aviation Administration said in a statement, according to the Times. “If a company is not authorized to conduct flights in bad-weather conditions, the pilot while flying for that company can only conduct flights in visual conditions.”

The lack of certification for Island Express Helicopters could explain why Zobayan did not file an instrument flight plan that would have allowed him to fly above the heavy fog, the New York Times reported. Instead, he had asked to fly under special visual flight rules.

Investigators combing through the crash site are focusing on weather as well as other possible causes, and have asked the public to send in any photos that show conditions near the crash on Sunday.

Low clouds and fog were present in the area at the time of the crash. When the helicopter took off from John Wayne Airport at 9:06 a.m. Sunday, visibility on the ground was only about 3 or 4 miles and the lowest overcast cloud layer was only 1,000 to 1,500 feet above ground level, according to weather.com meteorologist Brian Donegan.

Witnesses on the ground reported seeing the helicopter fly through thick clouds and fog just before it crashed.

Images posted from the crash scene by the Los Angeles County Sheriff's Office showed heavy fog shrouding the mountains and surrounding area.

A pilot flying under visual rules uses the horizon to keep the aircraft level. Randy Waldman, a helicopter flight instructor in Los Angeles, told the Los Angeles Times that Zobayan may have lost sight of the horizon and become disoriented in the foggy soup, causing a fatal descent.

“It’s very possible that it went from bad visibility to no visibility in a second. The top of the hillside that morning was completely obscured," Waldman said.

“At that point it was too late to do anything."

The crash on Jan. 26 killed all nine people onboard: Bryant and Gianna; Zobayan; Alyssa, John and Keri Altobelli; Payton and Sarah Chester and Christina Mauser.

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