What happened
The aircraft was engaged in an aerial application maneuver when the pilot lost control of the tail rotor. Shortly thereafter, the aircraft collided with the ground. The failure occurred during active operations rather than during takeoff or landing phases.
The investigation
Post-accident examination included a detailed metallurgical analysis of the failed components. Investigators discovered a fatigue fracture on the tail rotor drive shaft. The specific part involved was identified by manufacturer part number 47644179-9. The presence of the fatigue fracture indicates that the structural integrity of the shaft was compromised prior to the accident sequence.
Findings
The primary finding is the fatigue fracture of the tail rotor drive shaft. This mechanical failure directly caused the pilot to lose tail rotor control. Without effective anti-torque capability, the aircraft became uncontrollable, leading to the ground impact. The investigation confirmed that the failure was not due to external impact or immediate overload but rather a progressive material defect.
Safety message
This incident highlights the critical importance of regular inspection and maintenance of helicopter drive shafts, particularly those subjected to cyclic loading during agricultural operations. Preventive maintenance programs must account for fatigue life limits to avoid in-flight structural failures.