BARTOW, Fla. -- Dense fog compelled pilot John Shannon to request a tow to help get his plane to the ramp before takeoff.

The fog also would force him to use an instrument flight rules plan to get to Key West on Christmas Eve -- it was too thick at less than a quarter-mile to fly his Cessna 340 without visual cues.

Such was outlined in the National Transportation Safety Board's preliminary report of the Bartow airport plane crash, released Tuesday, Jan. 2. Shannon, a 70-year-old Lakeland attorney, was killed during takeoff.

More: Here's what we know about the 5 Christmas Eve plane crash victims

Also killed were his two daughters, Olivia Shannon, 24, a student at Southeastern University in Lakeland, and Victoria Shannon Worthington, 26, a Baltimore teacher; his son-in-law, Peter Worthington, 27, a University of Maryland law student; and a family friend, Krista Clayton, 32, a teacher in Lakeland.

The cause of death for four of the passengers was determined to be blunt force trauma and all of the deaths were ruled as accidental. Shannon's cause of death is not yet known.

(from left to right) John Shannon, 70, Victoria Shannon Worthington, 26, Olivia Shannon, 24, Peter Worthington Jr., 27, Krista Clayton, 27.

The preliminary report does not definitively conclude fog was the main cause of the crash, however, it was an issue throughout the morning. Shannon requested that the plane be towed from the pilot's hangar to the ramp, according to two airport employees in the NTSB report.

"The pilot wanted a tow because he didn't want to taxi next to the other hangars with the reduced visibility due to the dense fog," the report reads.

The request was carried out, and the five occupants were able to taxi the plane from the ramp to the end of the runway.

The employees reported they heard the plane take off and head east. Moments later, they heard an explosion, drove to it and found the wreckage on fire.

Photos: 5 people killed in twin-engine plane crash at Bartow airport

A helicopter pilot who earlier was reported to be taking pictures of the dense fog at the airport reported to the NTSB he heard a "pop" followed by hearing the explosion.

"There was no chance of survival," said Polk County Sheriff Grady Judd in the hours after the crash. "When you look at the crash, the only thing that you say is, 'Nobody suffered.'"

Shannon carried a private pilot's license since October 2010 with an instrument rating that allows a pilot to fly solely by referring to flight instruments in clouds or low visibility, according to Federal Aviation Administration records.

The Bartow airport air traffic control tower was closed at the time of the crash.

Contributing: USA Today

â–ºMake it easy to keep up-to-date with more stories like this. Download the 10News app now.

Have a news tip? Email, or visit our Facebook page or Twitter feed.