Unfortunately, there is still a lot we don't know about what caused a plane crash in Bartow on Christmas Eve that killed all five people on board, four were from the same family.

Almost immediately after the crash, Polk County Sheriff Grady Judd said the heavy fog over the area during take-off was likely a factor. Around the time of the crash, a National Weather Service observation reported visibility at the Bartow airport to be less than a quarter-mile because of fog.

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But in the days since, several friends of the pilot, prominent Lakeland lawyer John Shannon, have told 10News they believe something else must've happened.

Ron Pennekamp, the senior pastor at St. Paul Lutheran Lakeland and a close friend of Shannon's, called the 70-year-old a "master pilot," adding that he'd even flown with him on one occasion during which he landed in heavy fog.

RELATED: Lakeland pastor knew all 5 Christmas Eve plane crash, victims

"I don't think its fog, honestly, I really don't," Pennekamp told 10News on Monday. "I don't think he would've taken off if he thought he would put his family in jeopardy.”

It's now up to the NTSB and FAA to determine what caused the crash.

In the video above, watch 10News reporter Josh Sidorowicz hop into a flight simulator at the Sim Center in Clearwater with a commercial pilot and 10News aviation expert Mark Weinkrantz to learn how pilots operate in low visibility conditions.

With the simulator set to the Bartow Municipal Airport and the level of visibility just as it was at the time of the crash—less than a quarter-mile—Weinkrantz noted it's nearly impossible to see just a few hundred feet ahead from the cockpit.

"You can't see your hand in front of your face," he said. "We can take off in commercial airlines with just a few hundred feet of runway visible because we have much more sophisticated instruments in the cockpit and runways up to a higher specification for guidance.”

Even for an instrument-rated pilot, Weinkrantz said, the instruments are really for flying in the sky, not take-off.

Weinkrantz also noted the lack of center-line lighting down the middle of the runway at the Bartow airport and the lack of lighting at the end of the runway. The lighting, he says, can help a pilot maintain directional control.

It's possible, Weinkrantz said, that because Shannon couldn't gauge where he was in relation to the end of the runway, he might've pulled up too quickly, which would've changed the pitch of the plane too dramatically, causing it to fall back down.

"Bartow is not that sophisticated of an airport," Weinkrantz said. "As you're going faster and faster, you might only be able to see one or two lights right out ahead of you, but without those lights, you're hoping to see those white stripes in a gray sky and that's hard to do.”

According to data from the National Weather Service, 440 people on average are killed each year in plane crashes due to weather conditions like fog. According to the Aircraft Owners and Pilots Association, most general aviation accidents involve some kind of pilot error and while there are many factors that can contribute to this, bad weather is the number one culprit, the New York Times previously reported.

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