Accident Sequence
During an attempted takeoff, the helicopter's engine lost power, resulting in a hard landing. Just before the accident flight, maintenance had been performed on the helicopter: the adjusted valve assembly on the engine was removed and replaced. After this maintenance, the pilot flew the helicopter to a hospital, where a flight paramedic and a nurse boarded. Upon liftoff from the hospital, the engine again lost power, and the helicopter landed hard.
Post-Accident Examination
A post-accident test run and examination of the engine revealed that uncommanded engine shutdowns would occur at higher power settings. Disassembly of the adjusted valve assembly showed that the stop electro valve was internally damaged. The damage consisted of a deformation of the core housing, which prevented the stop electro valve from fully opening during operation. In this condition, a pressure drop occurred, leading to an untimely activation of the stop purge valve and a subsequent drop in fuel flow.
Component History
The adjusted valve assembly had been overhauled by the engine manufacturer and then sold to the operator before installation on the engine. According to the engine manufacturer, the damage occurred between the time the component was shipped from the factory and its first use, but they could not determine how the damage occurred. The damage was not visible until the unit was disassembled. Metallurgical examination indicated that the damage occurred when the valve was in a disassembled condition.