Incident Overview
While preparing for a flight, the pilot started the engine and taxied the aircraft to the chemical loading area. After leaving the engine running, he exited the aircraft to fill its chemical tank. As he prepared to do so, he heard the engine's RPM increase. The aircraft then began moving without anyone at the controls. Before the pilot could intervene, the aircraft collided with a ditch and came to rest.
Postaccident Findings
Examination after the accident revealed that the throttle cable had broken. According to the operator, the throttle arm on the carburetor is spring-loaded to the full throttle position. This configuration likely caused the engine to accelerate when the cable failed.
Sequence of Events
The pilot had left the aircraft unattended with the engine running. The broken throttle cable resulted in an unintended increase in engine power, leading to the aircraft's forward movement. The ditch subsequently stopped the aircraft's motion.