Accident Narrative
The pilot, with 3,807 hours of flight experience, had just departed a private heliport on a hot day. The helicopter was approximately 70 pounds under its certified gross weight. According to the pilot, the take-off was normal, and the helicopter climbed slowly. He then increased the climb rate with a slight rearward cyclic movement. The helicopter initially climbed but immediately began to descend. During the descent, the pilot attempted to dump the chemical load, but the dump doors failed to operate until his fourth try. Shortly thereafter, the main rotor blades struck trees, and the helicopter descended to the ground, coming to rest in an upright position.
Investigation
Examination of the helicopter and the dump valves revealed no mechanical deficiencies. The published Hover Ceiling in Ground Effect performance chart was interpolated and showed that the helicopter was within the performance envelope at the time. The investigator-in-charge calculated the density altitude to be 3,155 feet.
Vortex Ring State Discussion
The Federal Aviation Administration (FAA) Rotorcraft Flying Handbook defines vortex ring state (settling with power) on pages 11-5 to 11-7: "Vortex ring state describes an aerodynamic condition where a helicopter may be in a vertical descent with up to maximum power applied, and little or no cyclic authority. The term 'settling with power' comes from the fact that the helicopter keeps settling even though full engine power is applied."