Horner, an avid flyer, was piloting the small plane when it crashed approximately 60 miles north of Santa Barbara.
"We have lost an amazing person with a huge heart, and unbelievable talent," Horner's assistant Sylvia Patrycja wrote on Facebook. "He died doing what he loved. Thank you for all your support and love and see you down the road."
Horner produced more than 150 scores throughout his career, garnering 10 Oscar nominations and two wins for his work on Titanic. He also created the iconic soundtracks for Field of Dreams, A Beautiful Mind, two Star Trek movies and the upcoming Jake Gyllenhaal film Southpaw.