Incident Overview
While executing a turn to reverse direction during a chemical dispersal operation over a peanut crop, the aircraft's engine experienced a loss of power. The pilot responded by dumping the chemical load and performing a forced landing characterized as a hard full stall in the peanut field.
Findings
Post-accident inspection of the engine identified that the left magneto impulse coupling had failed. Fragments from the failed coupling became lodged in the engine's accessory case, subsequently separating the camshaft drive gear. This mechanical disruption rendered the engine powerless.
Regulatory Compliance
Airworthiness Directive AD78-09-07 R3 mandates inspection of the impulse coupling at intervals not exceeding 500 hours of time in service. At the time of the accident, the magneto in question had accumulated 576 hours of service and had not undergone the required inspection.