What happened
While returning to reload after dispensing a chemical load, the pilot experienced rough engine operation. The pilot noted erratic fuel flow and activated the boost pump, which provided momentary stabilization. However, smoke subsequently entered the cockpit and the engine began surging.
The pilot performed an emergency landing on rough/uneven terrain, which caused damage to the aircraft. During the landing, the aircraft went over on its nose. While the lap belt remained functional, the shoulder harness failed during the impact. The pilot evacuated the aircraft after it came to rest; however, the aircraft was subsequently destroyed by fire.
The investigation
An examination of the engine revealed a hole in the exhaust pipe located on the right side of the engine. This hole was positioned near the EGT probe and allowed exhaust gases to be directed toward the electrical wires and fuel lines. Due to the destruction caused by the fire, the specific mode of failure for the shoulder harness could not be determined.