Incident Overview
A public-use helicopter was conducting a fire fighting support mission, transporting personnel to a forest fire near a small lake in the Sierra Nevada Mountains. The pilot reported that upon arriving at the lake, he assessed the landing area as suitable, with surrounding obstructions consisting of fifty-foot-tall trees. After landing on the beach, the crew was informed that their services were no longer required.
Takeoff and Loss of Control
As the pilot initiated a lift-off from the lake edge, he experienced a depletion of blade pitch and available power while attempting to climb above the trees. He reversed direction, but during the turn the helicopter began a rapid descent toward the water. The pilot attempted to accelerate and increase power, but the rotor rpm started to droop. The helicopter subsequently settled into the lake with approximately 10 knots of forward airspeed, remaining upright with its skids immersed and rotor rpm reduced.
Attempted Recovery and Rollover
The pilot reduced collective pitch to recover rotor rpm, intending to hover the helicopter back to the beach. Once rotor rpm returned to normal, he increased collective. At that point, the helicopter rolled to the right and sank inverted.
Weight and Performance Analysis
A review of the cargo manifest, load calculation sheet, and hover ceiling chart indicated that the helicopter was approximately 800 pounds over the hover out of ground effect ceiling for the existing temperature and pressure altitude. The density altitude at the time was computed to be about 9,500 feet.