What happened
On July 11, 2008, a Sikorsky S-76C, registration PR-LCE, operated by Líder Táxi Aéreo, departed from the P-33 platform in the Campos Basin, Brazil, en route to the São Tomé helipad. During the cruise phase of the flight, the crew detected abnormal noise and intense vibrations throughout the aircraft. Although engine performance parameters remained within normal limits, the crew decided to perform a precautionary landing at the nearest available platform, P-20.
Upon landing, the crew inspected the Main Gear Box area and discovered damage to the flexible coupling located between the engine 1 drive shaft and the Main Gear Box Input Flange. Subsequent maintenance efforts revealed that all blades within the flexible coupling were completely fractured and deformed. Due to the severity of the damage, the aircraft could not return to base under its own power and required transport via sea.
The investigation
CENIPA's investigation focused on the condition of the flexible coupling (P/N 76361-04008-103) and the maintenance history of the aircraft. The investigation established that the aircraft had undergone a 900-hour inspection earlier in 2008, which required the removal and inspection of this specific component. However, the investigation found that the maintenance performed during recent inspections was inadequate.
Technical analysis of the component revealed widespread pitting and general corrosion, as well as corrosion caused by foreign products on the surface. The investigation determined that the blades failed due to the formation of pre-cracks in areas affected by corrosion, which eventually led to an overload of the remaining blades. Furthermore, the investigation found that the maintenance personnel used an improper abrasive material during repair/inspection, which degraded the protective surface layer of the blades. The investigation also noted that the maintenance environment lacked the necessary conditions to comply with the manufacturer's manual requirements.
Findings
- Inadequate maintenance execution: The methods used during previous inspections were inefficient, and the use of an incorrect abrasive grit size contributed to the degradation of the component's surface.
- Lack of training: Both the maintenance technician and the inspector lacked the necessary knowledge and specific training required to perform the mandatory inspection of the flexible coupling.
- Supervisory failure: The designated inspector failed to identify the use of improper abrasives and the presence of corrosion on the component.
- Inadequate oversight: The operator's continuous analysis and supervision system failed to detect significant deficiencies within the airworthiness maintenance program.
- Effective crew decision-making: The crew's decision to perform a precautionary landing was a decisive factor in preventing a potentially catastrophic accident.