The 24-year-old pilot killed in a fiery plane crash at Knox County Regional Airport was described by family and friends Sunday as a natural leader who was about to leave for flight school to become a pilot in the Air Force.

William Hannigan III, known to his family as B.J. and his friends as Will, was on active duty with the 101st Air Refueling Wing in Bangor. A native of Portland, he was a 2006 graduate of Cheverus High School, where he was the football team captain. He graduated from the University of Maine in 2011 with a degree in civil engineering.

“He had a lot of energy,” said his father, William Hannigan of Portland.

The father said his son fell in love with flying during a surprise birthday flight in a World War II fighter plane over Lake Champlain in Vermont.

“That might have been what did it,” William Hannigan said.

The younger Hannigan was taking two of his fellow Lambda Chi Alpha fraternity brothers on a flight when the Cessna 172 he had rented struck a pickup truck that was crossing the main runway at the airport. The plane continued to climb to about 150 feet before it crashed into woods to the left of the runway.

Also killed in the crash were David Cheney, 22, of Beverly, Mass., and Marcelo Rugini, a foreign exchange student from Brazil who was living in Nobleboro.

Investigators from the Federal Aviation Administration and the National Transportation Safety Board were continuing to try to determine how the crash took place. The driver of the truck, Stephen Turner, 62, of Camden, was not hurt and has not been charged.

Knox airport manager Jeff Northgraves said drivers there are allowed to cross runways as long as they have training from airport officials and a vehicle that’s equipped with a radio. Turner is a local pilot who has been trained and had a radio in the truck.

, Northgraves said.

Knox’s regional airport does not have a control tower or anyone monitoring aircraft or vehicle traffic, he said.

On Sunday, William Hannigan said the three young men in the plane were close friends. Cheney was the president of the fraternity and attended Hannigan’s college graduation and family party. Rugini was the sophisticate of the group.

“He was a very dynamic person, on top of the styles,” said William Hannigan.

Will Hannigan played ice hockey both in high school and with the National Guard. He spent several months last year in Qatar with the National Guard.

His family said people sought out Hannigan’s company.

“When he came by, we couldn’t wait to come over and see what was new with him,” said Joe Hannigan of Portland, Will’s uncle.

Will Hannigan’s mother is Carolyn Dorr of Windham. He is also survived by his younger sister, Alyx Hannigan, and a stepbrother, Justin Hayden.