NTSB Identification: ANC98LA109.
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Nonscheduled 14 CFR
Accident occurred Saturday, July 25, 1998 in SKWENTNA, AK
Probable Cause Approval Date: 03/30/2000
Aircraft: Enstrom F-28F, registration: N8622U
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 certificated commercial helicopter pilot was conducting a salmon survey for the State of Alaska, Department of Fish & Game. This operation required him to hover the helicopter over the stream while the passenger, a wildlife biologist employed by the State of Alaska, noted the number of fish. The pilot stated that while in a hover above the stream, he felt a slight vibration followed by a partial loss of engine power. He said that while hover taxiing the helicopter to a suitable landing area, the engine continued to lose power, and he was forced to make a downwind autorotation. He said that as the helicopter touched down, the main rotor blades flexed downward, and struck the tail boom. The helicopter's tail boom, and tail rotor gearbox sustained substantial damage. The operator reported that during a postaccident inspection of the engine, a fractured intake manifold flange was discovered on the number three cylinder assembly.

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

A loss of engine power due to a fractured number three cylinder intake manifold flange, and the pilot's inability to maintain the proper rate of descent during the autorotation flare. A contributing factor associated with the accident was the downwind (tailwind) landing condition.

Full narrative available

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