Incident Overview
A helicopter pilot reported that after completing aerial application of mosquito control treatment and returning to the load site, the aircraft was in cruise flight at 300 feet above ground level when the pilot noticed it required more right cyclic control to keep the helicopter level. The pilot also began to experience a loss in altitude. The rotor RPM had dropped to 90%, but there were no warning lights or horns. The engine out audio warning was placarded as inoperative, and the pilot was aware that the oil chip warning light was also inoperative.
Forced Landing
The pilot executed a forced landing in an alfalfa field. Due to the right cyclic input required, the pilot stated that the landing involved a drift to the right, causing the right skid gear to snap and the helicopter to roll over onto its right side.
Investigation Findings
An investigation revealed that the left hopper was blocked and still contained an estimated 100 to 300 pounds of mosquito control agent. This unbalanced load was countered by extreme cyclic input. Examination of the engine disclosed severe erosion of the compressor blades, and horsepower production was significantly below production test specifications.