Incident Overview
A helicopter collided with trees and terrain while the pilot maneuvered at a low altitude, under high density altitude conditions, over rising mountainous terrain. The purpose of the aerial survey flight was to provide a California Department of Forestry passenger with an aerial mapping opportunity around active fire areas in Lassen National Park.
Flight Details
According to the pilot, his specific mission was to maneuver the helicopter over a route that would allow the front seat passenger to accurately mark global positioning satellite (GPS) waypoints around the fire area. Initially, the pilot flew at 6,500 feet mean sea level (msl). When the passenger began marking waypoints, the pilot descended to 5,500 feet msl. The pilot further indicated that he made several turns during the flight. Just before the crash, he flew in a southerly direction, then a northerly direction. When he next turned to an east-southeasterly direction, he raised the collective, observed his proximity to the fire line, and directed his attention to a hill that he was approaching. The pilot indicated that he had expected to be higher than the top of the hill, but he was lower. Despite his efforts to increase altitude, the helicopter impacted trees and terrain.
Witness Observations
Ground-based witnesses reported that the helicopter had been maneuvering between 50 and 75 feet above ground level (AGL), in a downwind direction, over 5,100-foot msl upsloping terrain, toward the crest of the mountain. The surface wind was from the north-northeast at about 10 knots. The temperature was almost 90 degrees Fahrenheit. The witnesses further stated that the helicopter's engine was operating until it impacted trees, about 20 feet beneath the mountain crest.
Conclusion
The accident involved a collision with trees and terrain during a low-altitude maneuver under high density altitude conditions over rising terrain. The source provides no further details or analysis.