What happened
The pilot was conducting an agricultural application flight when the incident occurred. After completing one spray pass, the pilot initiated a pull-up maneuver to begin another pass over the target area. During this climb phase, the aircraft engine experienced a sudden loss of power. Unable to maintain altitude or control, the airplane descended and impacted an adjacent field.
The investigation
A mechanic subsequently examined the aircraft engine to determine the cause of the failure. The inspection revealed significant mechanical damage on the intake side of the number five cylinder. Specifically, the retaining spring for the intake valve was found missing. Additionally, cracks were identified in the intake pipe casting associated with that cylinder.
Findings
The mechanical evidence points to a catastrophic internal engine failure. The absence of the valve retaining spring suggests a component separation or fatigue failure. This allowed the valve to malfunction, likely leading to further damage and the subsequent loss of power. The cracks in the intake pipe casting indicate stress or material failure that may have contributed to the overall engine breakdown.
Safety message
Regular inspection of cylinder components, particularly valve springs and intake passages, is critical for agricultural aircraft operating under high-stress conditions. Early detection of fatigue cracks or missing hardware can prevent in-flight power loss.