Incident Overview
An agricultural pilot experienced an in-flight emergency while pulling up from a low-level pass. The pilot detected an odor described as "like wires burning" and observed a drop in engine fuel pressure. In response, the pilot selected the auxiliary fuel pump to the "EMERGENCY" position. Five to ten seconds later, the engine lost partial power. Unable to maintain altitude, the pilot decided to land the airplane in a rolling wheat field. During the landing, the airplane nosed over and came to rest inverted.
Post-Accident Examination
An examination of the airplane revealed that, prior to impact, the engine exhaust stack had separated from the muffler. This separation caused hot exhaust gases, normally vented overboard, to be directed toward the airplane's firewall. The resulting thermal effects damaged electrical wiring and created a vapor condition in the fuel gascolator. The pilot attempted to purge the vapor but was unsuccessful. No other pre-impact anomalies were noted with the engine or the fuel system that would have prevented normal operating power.