Accident
A helicopter engaged in water dropping operations as part of an ongoing forest fire fighting effort experienced an engine flameout and subsequent crash. According to a firefighter on scene, the helicopter had completed two water drops before the accident. A battalion fire chief directing the effort observed the helicopter making water drops on a slope. After a drop that involved an abrupt pull-up and turn following water release from the bucket, the fire chief heard the words 'May Day,' 'I have a flame out,' and finally 'I'm going down' over the radio. Several other individuals monitoring the common frequency also reported hearing a transmission containing the phrase 'flame out.' The helicopter ultimately impacted the bottom of the canyon.
Investigation
Post-accident inspection of the helicopter's fuel system revealed that the lines from the engine fuel nozzle to the fuel control and the airframe fuel filter contained fuel. The lines and in-line filters held both fuel and particulate matter in the bottom of both filter housings. Testing determined that the manifold check valve leaked from both inlet ports. Upon disassembly of the valves, additional foreign material was found, consisting of a combination of organic and inorganic materials.
A 5-gallon fuel sample was taken from the refueling truck on the day of the accident. Analytical report results indicated that the sample was aviation turbine fuel with no contamination noted.
Historical records show a series of engine flameout related accidents and incidents associated with this engine make and model. Controlled tests have demonstrated that if entrapped air migrates through the fuel system to the engine, an engine flameout can occur.
Findings
The investigation identified fuel system issues including particulate contamination in filters, a leaking manifold check valve, and foreign material in valves. However, the fuel source from the refueling truck was found to be uncontaminated. The exact cause of the flameout was not definitively stated in the source material.