What happened
On February 10, 2016, a Sikorsky S-7/6C, registration PR-LDM, operated by Líder Táxi Aéreo SA, was performing a passenger transport flight from the Merluza offshore platform to the Itanhaém Aerodrome (SDIM) in São Paulo. The aircraft was carrying two crew members and nine passengers.
During the approach and landing phase at Itanhaém, the pilot noticed abnormal vibrations through the flight controls (pedals). Following the landing, the crew reported the anomaly to the company's maintenance department. A subsequent inspection of the tail rotor system revealed that one of the four pitch control rods had fractured.
While the aircraft sustained light damage, all 11 occupants were unharmed.
The investigation
CENIPA investigators examined the aircraft's maintenance records, which showed that recent 50-hour and 100-hour inspections had been performed correctly and according to the manufacturer's requirements. The investigation focused on the physical state of the tail rotor components.
The fractured pitch control rod was sent to the Institute of Aeronautics and Space (IAE) for failure analysis. Visual and stereoscopic examinations of the broken part revealed a fracture in the thread near the eyelet. However, the analysis also showed significant plastic deformation (crushing) on the fracture surface. This deformation occurred after the initial rupture, likely due to impact, which obscured the original crack's origin.
Investigators also noted that post-incident maintenance actions, including the replacement of all four rods and the transfer of the broken part to a private company for testing, were conducted without coordination with the SIPAER investigation system. This handling potentially removed evidence regarding the component's installation condition at the time of the failure.
Findings
- The fracture of a tail rotor pitch control rod was the primary cause of the abnormal vibrations.
- The root cause of the material failure could not be determined because the fracture surface was too deformed to identify the crack's origin.
- Maintenance practices for the aircraft were found to be in compliance with established intervals and procedures.
- Post-occurrence handling of the failed component and the aircraft's parts occurred without the required coordination with the investigation authority.