Family members say one of the victims was a certified flight instructor.
Sixty-five-year-old Scott Clark's family tells ABC7 they believe he was co-piloting the single-engine private plane Thursday afternoon when something went wrong.
Clark and the plane's owner, Paul Sanfilippo, 82, of Grayslake, had some kind of trouble and the plane went down just east of the Lake in the Hills airport. Clark's family describes him as an adventurous man with a passion for airplanes.
"He was kind, he had the biggest heart of anyone, he was such a good father, and he understood me so well," said Elizabeth Clark, daughter.
Clark's family plans to hold a memorial service in his honor next week.