"He`s an experienced pilot, but I know nothing else," Cooper told Reuters.
Local fire authorities said the 9:30 a.m. crash of the five-passenger plane left an impact crater and sparked a fire that charred more than an acre of brush, and that there were no survivors.
Captain Mike Lindbery of the Ventura County Fire Department said only one set of remains was found, but he did not know whether the crash victim had been positively identified.
The cause of the crash was not immediately known.
Horner won two Academy Awards for his work on "Titanic" - one for the movie`s score and one he shared with lyricist Will Jennings for best original song, "My Heart Will Go On," performed by Celine Dion.
Horner also composed the music for an array of other major films, including "Aliens," "The Karate Kid," and "Braveheart." His scores for "Avatar," "A Beautiful Mind" and "House of Sand and Fog" earned Oscar nominations.
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