Incident Description
A helicopter was in cruise flight over the Gulf of Mexico when it began to vibrate and shudder. The pilot lowered the collective control to initiate an autorotation, and the engine lost power. During the ensuing autorotation, the helicopter's floats were deployed. The pilot attempted to decelerate the helicopter; however, the controls became stiff, and subsequently, the helicopter hit the water hard.
Fuel System Examination
Examination of the helicopter's fuel system revealed that the fuel nozzle inlet screen was collapsed and the screen was 80 to 90% contaminated with a brown material with a polymeric-like to varnish-like appearance. The screen was examined by a laboratory, and it was determined that DIEGME, a fuel additive used as an icing inhibitor, was present on the screen.
Environmental Factors
The helicopter's operating environment is such that salt water could have been introduced into the fuel system. The presence of water and fuel would allow bacteria to grow. The combination of bacterial growth, DIEGME, and water resulted in the formation of an "apple-jelly" type material, which then adhered to the fuel system components (fuel nozzle screen).
Conclusion
The blockage and collapse of the fuel nozzle screen resulted in an interruption of fuel flow, and the subsequent loss of engine power.