What happened
On June 6, 2022, at 17:34 UTC, a Robinson R-22 Beta II helicopter, registration LV-JUD, was performing a vertical takeoff at San Fernando International Airport in Buenos Aires, Argentina. During the initial climb, the pilot experienced a sudden, sharp increase in engine power. Simultaneously, one of the tail rotor blades detached from the assembly, accompanied by abnormal noises. The pilot immediately aborted the maneuver, resulting in significant damage to the aircraft' and the tail cone section.
The investigation
Investigators examined the wreckage and identified extensive damage to the tail assembly, including the stabilizer, transmission box, and tail rotor blades. The investigation revealed that the tail rotor blades had fractured due to loads exceeding the material's strength, which also caused impact marks on the vertical stabilizer. The transmission shaft and the pitch change bar also showed plastic deformation and subsequent fractures caused by excessive loads.
Laboratory analysis at the Fábrica Argentina de Aviones (FAdeA) identified casting defects, specifically shrinkage cavities, in the aluminum alloy component that joins the stabilizer to the tail cone. While the manufacturer, Robinson Helicopter Company, noted that these imperfections were within acceptable manufacturing standards, they acknowledged that such defects could impact structural resistance. Furthermore, investigators explored the possibility of a "third whirl mode"—a phenomenon where the tail rotor shaft exceeds approximately 130% of its nominal RPM—which could lead to the observed structural failures.
Findings
- The tail rotor blades fractured because they were subjected to loads exceeding the material's ultimate strength.
- The transmission shaft and pitch change bar experienced plastic deformation and fracture due to excessive mechanical loads.
- The aluminum connection piece between the stabilizer and the tail cone contained manufacturing defects (shrinkage cavities) that could facilitate crack propagation.
- A sudden engine acceleration occurred during the takeoff phase, potentially triggering the mechanical failure.
- There was no evidence of previous hard landings that would have caused misalignment of the transmission shaft.