He was 61.
According to the Hollywood Reporter, the plane was immediately destroyed on impact and the pilot was alone in the aircraft when it crashed.
Fire officials reported that they found the burning wreckage in the west of the Highway 33 in Southern California, and within the one-acre burn zone discovered the tail section of the two-seater S312 Tucano MK1 single-engine turboprop plane, which was registered in composer's name.
Horner's assistant, Sylvia Patrycja confirmed the news on the musician's official page saying that a great tragedy has struck his family as they have lost an amazing person with a huge heart, and unbelievable talent.
Horner was known for the brilliant music composition for Field of Dreams, Braveheart and Titanic for which he won two Academy Awards.
His score for the Titanic sold 27 million copies worldwide.
Photograph: Sean Gallup/Getty Images