What happened
The THE AG aircraft was engaged in agricultural operations, specifically spraying Nudrin on soybean crops. During this phase of flight, the engine experienced a sudden loss of power. Unable to maintain altitude or continue the mission, the pilot initiated an emergency procedure and executed a forced landing in an adjacent rice field.
Upon impact with the ground, the aircraft flipped forward, coming to rest in an inverted position. The force of the crash resulted in significant structural damage to the airframe. No further details regarding injuries to the pilot or passengers were provided in the source documentation.
The investigation
A thorough examination of the accident site and the aircraft components was conducted to determine the root cause of the engine failure. Investigators focused primarily on the mechanical integrity of the propulsion system, given the sudden nature of the power loss.
The inspection revealed a critical mechanical failure within the engine's reduction gear assembly. Specifically, the two-piece cam reduction gear had separated and come apart during operation. This disintegration caused the immediate cessation of engine function, leading directly to the forced landing scenario described above.
Findings
The investigation uncovered a regulatory compliance issue related to the maintenance history of the aircraft's engine. An Airworthiness Directive (AD) was issued in 1966 that mandated the replacement of the two-piece cam reduction gear with a more reliable one-piece gear design. This directive required the modification to be completed at the next engine overhaul occurring after September 7, 1966.
Records indicated that the engine involved in this accident had received its last overhaul prior to the issuance of that Airworthiness Directive. Consequently, the engine retained the original two-piece cam reduction gear design, which was known to be susceptible to failure. The separation of these components is identified as the primary mechanical cause of the accident.
Safety message
Adherence to Airworthiness Directives is critical for maintaining aircraft safety. Operators must ensure that all mandated modifications, particularly those addressing known mechanical weaknesses like gear failures, are completed promptly during scheduled maintenance intervals.