NTSB Identification: LAX05LA022.
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Accident occurred Sunday, October 31, 2004 in San Martin, CA
Probable Cause Approval Date: 02/28/2006
Aircraft: Bell 47D1, registration: N903B
Injuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

The helicopter experienced a loss of engine power and rolled over during an attempted autorotation to a soft, muddy field. The helicopter departed for a 22-nautical mile training flight with 10 gallons of fuel remaining in the 28-gallon fuel tank. While en route, both the certified flight instructor (CFI) and student pilot noted that an unusually high application of carburetor heat was required to keep the inlet temperature needle within the normal range. With the intention of entering the traffic pattern at the destination airport, the student pilot initiated a descent and maneuvered the helicopter in a right turn. With the helicopter configured in the right turn, about 500 feet above ground level (agl), the engine experienced a momentary power interruption and subsequently stopped. The student pilot executed an autorotation and the helicopter touched down in a crop field. The right skid dug into the soft muddy field, resulting in the helicopter rotating around the skid and coming to rest on its right side. The fuel tank contained about 5 gallons of fuel just prior to the accident. Due to the orientation of the fuel outlet port inside the fuel tank, the helicopter is susceptible to unporting with low quantities of fuel present during maneuvers. With the outlet located on the left side of the tank, when a helicopter is in a right turn with minimal fuel onboard, the outlet can intake air resulting in fuel starvation to the engine. According to a standard reference icing probability chart, the atmospheric conditions present at the time of the accident were in the range considered favorable for carburetor ice formation.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

A loss of power for undetermined reasons.

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