DEN06LA094 · Cessna 180

Prior to departure, the airplane had been refueled with 37.5 gallons of 100 low lead fuel. Shortly after takeoff from runway 23, the pilot "heard a pop/bang from the engine...engine seemed to lose power." The pilot stated that he felt a "severe vibration" after the pop/bang engine noise. The pilot executed a 180-degree left turn in an attempt to return to the airport. Subsequently, the airplane landed in a grass field, impacted a dirt embankment and a fence, and came to rest upright in a ditch. Examination of the aircraft revealed that the throttle cable was routed above the rear mounted alternator belt, and the cable was resting on the alternator belt. The throttle cable shielding was worn through by contact with the alternator belt, and the braided cable was exposed. No damage was noted to the braided throttle cable. One of the tubes of the engine mounting frame was fractured; the fracture surfaces were consistent with an overload failure. Mechanical continuity throughout the engine was established when the propeller was rotated by hand, and the engine was test run on the airframe. The engine test run was performed for approximately 1 minute at an engine tachometer speed of 1,300 RPM. No anomalies were noted with the engine during the examination and test run. The reason for the partial loss of engine power could not be determined. A review of the airplane's logbooks revealed the airplane underwent annual and 100-hour inspections between the time the overhauled engine was installed on the airframe and the accident.

Verbatim NTSB analysis and probable cause from the NTSB dataset