What happened
The pilot reported that during level cruise flight at an altitude of 12,500 feet, the engine suddenly lost power. In response, the pilot switched fuel tanks and activated the boost pump, but these actions did not restore engine function. The pilot then entered a glide and directed the aircraft toward the Salida, Colorado, Airport. Upon landing, the airplane stopped short of the runway and struck a fence post.
The investigation
A postaccident examination of the engine revealed that the bolt securing the alternate air valve to its actuating shaft had failed. This failure allowed the alternate air valve to close unexpectedly, which effectively starved the engine of necessary air. Investigators located the other half of the broken bolt inside the No. 6 cylinder.
Findings
The primary mechanical issue was the failure of the bolt holding the alternate air valve. This component failure led directly to the engine starvation of air, causing the loss of power during cruise flight.