19980725017549A

Crashed en route, anchoragae, AK. (-23) on July 25, 1998, at approximately 1400, Alaska daylight time, an Enstrom F28F, N8622U helicopter landed hard after experiencing a loss of power, while counting fish for the department of fish and game on the upper talachulitna river. There were no injuries. The commercial certificated pilot was operating the flight in visual meteorological conditions. The pilot stated, during a telephone conversation, that after landing, he an exhaust gasket completely "completely blow out." The heat from the blown gasket apparently heated a bolt on the intake manifold and caused it to break and cause the intake manifold to come loose. The helicopter would not maintain operating RPM and the pilot was forced to land the helicopter. He also stated that the landing he made was a little downwind with low RPM, as he was unable to regain full RPM due to the mechanical failure. The helicopter sustained substantil damage to the main rotor blades and the tail rotor gear box during landing. (.4) 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.