Middle Fire Helicopter Midair Collision Fatality 1977

On the night of July 24, 1977, while supporting firefighting operations on the Middle Fire, a 3,800-acre wildfire in the Angeles National Forest, Thomas Grady of Los Angeles County Fire Department was tragically killed in the line of duty. During a nighttime landing at Mill Creek Heliport, the Bell 205 helicopter he was piloting collided mid-air with a U.S. Forest Service Bell 212. The accident seriously injured his co-pilot, Theodore Hellmers, and the two pilots of the other aircraft. This accident led the Forest Service to end its night-flying program on wildland fires for a period of about 35 years. 

Incident summary from Los Angeles County Firefighters Memorial