Introduction
A helicopter experienced a rotor RPM decay during takeoff from a field site, resulting in a rollover after touchdown. The incident occurred following a refueling and reloading operation with a spray solution.
Narrative
The pilot initiated a takeoff in calm wind conditions. The takeoff location required an upslope departure. During the upslope portion of the takeoff, the rotor RPM dropped slightly but remained within the green arc. As the helicopter crossed a fence and the terrain began sloping downhill, it flew out of ground effect.
The pilot reported leveling the helicopter and then beginning a slight descent to increase rotor RPM and airspeed. However, the rotor RPM continued to decay. Just before touchdown, the helicopter yawed 90 degrees to the right. After touchdown, the helicopter rolled onto its side.
Environmental Conditions
The density altitude at the site was estimated to be 3,216 feet.