What happened
Following takeoff, the Cessna (type not specified in source) performed a climbout over mountainous terrain. After successfully clearing the mountains, the pilot reduced engine power to descend into an open valley. While at approximately 1,800 feet above ground level, the pilot advanced the throttle but received no increase in engine power.
In response to the loss of power, the pilot declared an emergency and attempted an emergency landing on a narrow gravel bar situated next to a river. During the landing attempt, the main landing gear skimmed across the water and onto the edge of the gravel bar. The left main gear sank into the soft gravel at the water's edge, causing the aircraft to come to rest in an inverted position. The pilot was not injured.
The investigation
The pilot reported that an annual inspection had been completed 11 days before the accident, with only 3 flight hours accumulated since that service. A post-accident inspection of the throttle cable assembly revealed that the cable had become detached from the carburetor throttle arm. This detachment was caused by a missing bolt, nut, and cotter pin. The FAA could not independently verify the absence of these components because the pilot had repaired the aircraft and ferried it to a different location prior to investigation.