Incident Overview
During a turn for a spray pass, the pilot reported that the engine quit. He then opened the chemical dump valve and executed a landing perpendicular to plowed rows in a field. After touchdown, the aircraft nosed over. The pilot, who was unconscious, was cut free from his seatbelt and shoulder harness.
Post-Accident Examination
Examination of the aircraft at the accident site revealed that the magneto switch was positioned to 'BOTH.' The aircraft was recovered, and the engine was started and operated normally with the magneto switch in the BOTH position. However, when the magneto switch was moved to the LEFT position, the engine quit.
Magneto Inspection
The left magneto was removed for disassembly. Inspection revealed that a phenolic gear, which drives the rotating magnet, was damaged. This damage prevented the magneto from producing a spark.
Determination
Despite the findings, no determination could be made as to the reason for the loss of engine power.