How did Richard Bong die?

Richard Bong died in California on August 6th 1945. He was 24 years, 8 months and 13 days old when he died.In the Pacific Theater he flew the P-38 scoring 40 Victories against the Japanese and receiving the Congressional Medal of Honor for his achievements. Bong became a test pilot assigned to Lockheed on the P-80 Shooting Star project in Burbank, California in 1945 where he died during a routine test flight